25792 Federal Register / Vol. 77, No. 84 / Tuesday, May 1, 2012 / Proposed Rules 

DEPARTMENT OF THE INTERIOR 

Fish and Wildlife Service 

50 CFR Part 17 

[Docket No. FWS–R2–ES–2008–0059; 

4500030113] 

Endangered and Threatened Wildlife 

and Plants; 12-Month Finding on a 

Petition To List the Sonoran Desert 

Area Bald Eagle as Threatened or 

Endangered 

AGENCY: Fish and Wildlife Service, 

Interior. 

ACTION: Notice of 12-month petition 

finding. 

SUMMARY: We, the U.S. Fish and 

Wildlife Service (Service), announce a 

12-month finding on a petition to list 

the Sonoran Desert Area population of 

bald eagle (Haliaeetus leucocephalus) as 

threatened or endangered under the 

Endangered Species Act of 1973, as 

amended (Act). After review of the best 

available scientific and commercial 

information, we find that listing the 

Sonoran Desert Area population of bald 

eagle does not qualify as a distinct 

population segment (DPS) and listing 

the Sonoran Desert Area population of 

bald eagle is not warranted at this time. 

DATES: The finding announced in this 

document was made on May 1, 2012. 

ADDRESSES: This finding is available on 

the Internet at http:// 

www.regulations.gov at Docket Number 

FWS–R2–ES–2008–0059. Supporting 

documentation we used in preparing 

this finding is available for public 

inspection, by appointment, during 

normal business hours at the U.S. Fish 

and Wildlife Service, Southwest 

Regional Office, 500 Gold Ave. SW., 

Room 6034, Albuquerque, NM 87102. 

Please submit any new information, 

materials, comments, or questions 

concerning this finding to the above 

address. 

FOR FURTHER INFORMATION CONTACT: 

Michelle Shaughnessy, Assistant 

Regional Director, Southwest Regional 

Office (see ADDRESSES); by telephone at 

505–248–6920; or by facsimile at 505– 

248–6788. If you use a 

telecommunications device for the deaf 

(TDD), please call the Federal 

Information Relay Service (FIRS) at 

800–877–8339. 

SUPPLEMENTARY INFORMATION: 

Background 

Section 4(b)(3)(B) of the Act (16 

U.S.C. 1531 et seq.) requires that, for 

any petition to revise the Federal Lists 

of Endangered and Threatened Wildlife 

and Plants that contains substantial 

scientific or commercial information 

indicating that listing may be warranted, 

we make a finding within 12 months of 

the date of our receipt of the petition. In 

this finding we will determine that the 

petitioned action is: (1) Not warranted, 

(2) warranted, or (3) warranted, but the 

immediate proposal of a regulation is 

precluded by other pending proposals to 

determine whether species are 

threatened or endangered (warranted 

but precluded). Section 4(b)(3)(C) of the 

Act requires that we treat a petition for 

which the requested action is found to 

be warranted but precluded as though 

resubmitted on the date of such finding, 

that is, requiring that we make a 

subsequent finding within 12 months. 

Such 12-month findings must be 

published in the Federal Register. 

This document constitutes our revised 

12-month finding on a petition to list 

the Sonoran Desert Area bald eagle. In 

this document, the Sonoran Desert Area 

population is the name given to the 

entity under evaluation for designation 

as a distinct population segment (DPS). 

For the purposes of this assessment, the 

Sonoran Desert Area population 

includes all bald eagle territories within 

Arizona, the Copper Basin breeding area 

in California near the Colorado River, 

and the territories of interior Sonora, 

Mexico, that occur within the Sonoran 

Desert and adjacent transitional 

communities. For more detail on the 

boundary of the DPS, see the discussion 

below under Determination of the Area 

for Analysis. 

Previous Federal Action 

Bald eagles (Haliaeetus 

leucocephalus) gained protection under 

the Bald Eagle Protection Act (16 U.S.C. 

668–668d) in 1940 and the Migratory 

Bird Treaty Act (MBTA) (16 U.S.C. 703– 

712) in 1972. A 1962 amendment to the 

Bald Eagle Protection Act added 

protection for the golden eagle (Aquila 

chrysaetos), and the amended statute 

became known as the Bald and Golden 

Eagle Protection Act (BGEPA). On 

February 14, 1978, the Service listed the 

bald eagle as an endangered species 

under the Endangered Species Act of 

1973, as amended (Act) (16 U.S.C. 1531 

et seq.) in 43 of the contiguous States, 

and as a threatened species in the States 

of Michigan, Minnesota, Wisconsin, 

Oregon, and Washington (43 FR 6230). 

On July 12, 1995, we published a final 

rule to reclassify the bald eagle from 

endangered to threatened in the 43 

States where it had been listed as 

endangered and retain the threatened 

status for the other 5 States (60 FR 

36000). 

On July 6, 1999, we published a 

proposed rule to delist the bald eagle 

throughout the lower 48 States due to 

recovery (64 FR 36454). On February 16, 

2006, we reopened the public comment 

period to consider new information 

received on our July 6, 1999 (71 FR 

8238), proposed rule to delist the bald 

eagle in the lower 48 States. On October 

6, 2004, we received a petition from the 

Center for Biological Diversity (CBD), 

the Maricopa Audubon Society, and the 

Arizona Audubon Council requesting 

that the ‘‘Southwestern desert nesting 

bald eagle population’’ be classified as 

a distinct population segment (DPS) 

under the Act, that this DPS be 

reclassified from a threatened species to 

an endangered species, and that we 

concurrently designate critical habitat 

for the DPS under the Act. We 

announced in our 90-day finding on 

August 30, 2006 (71 FR 51549), that the 

petition did not present substantial 

scientific or commercial information 

indicating that the petitioned action 

may be warranted. 

On January 5, 2007, the CBD and the 

Maricopa Audubon Society (Plaintiffs) 

filed a lawsuit in the U.S. District Court 

for the District of Arizona challenging 

the Service’s 90-day finding that the 

bald eagles nesting in the Sonoran 

Desert area of central Arizona did not 

qualify as a DPS, and further 

challenging the Service’s 90-day finding 

that the population should not be 

uplisted to endangered status. 

On July 9, 2007 (72 FR 37346), we 

published the final delisting rule for 

bald eagles in the lower 48 States due 

to recovery. This final delisting rule also 

included the bald eagles located in the 

Sonoran Desert. On August 17, 2007, the 

CBD and the Maricopa Audubon Society 

filed a Motion for Summary Judgment in 

their January 5, 2007, lawsuit. In early 

2008, several Native American Tribes 

submitted amicus curiae (‘‘friend of the 

court’’) briefs in support of the August 

17, 2007, Motion for Summary 

Judgment. The San Carlos Apache Tribe, 

Yavapai-Apache Nation, and Tonto 

Apache Tribe submitted amicus curiae 

briefs to the court on January 29, 2008; 

the Salt River Pima-Maricopa Indian 

Community submitted an amicus curiae 

brief to the court on February 4, 2008; 

and the Fort McDowell Yavapai Nation 

submitted an amicus curiae brief to the 

court on February 7, 2008. 

On March 5, 2008, the court made a 

final decision in the challenge to the 

Service’s 2006 90-day finding, ruling in 

favor of the CBD and the Maricopa 

Audubon Society. The court order 

(Center for Biological Diversity v. 

Kempthorne, CV 07–0038–PHX–MHM 

(D. Ariz)), dated March 6, 2008, required 

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the Service to conduct a status review 

of the Desert bald eagle population 

pursuant to the Act to determine 

whether that population may qualify as 

a DPS, and if so, whether listing that 

DPS as threatened or endangered 

pursuant to the Act is warranted. The 

court enjoined the Service’s application 

of the July 9, 2007 (72 FR 37346), final 

delisting rule with respect to the bald 

eagles nesting in the Sonoran Desert 

area of central Arizona pending that 

status review and 12-month finding on 

the Plaintiffs’ petition. 

On May 1, 2008, to conform with the 

court’s March 6, 2008, order, we 

published a final rule listing the 

potential Sonoran Desert bald eagle DPS 

as threatened under the Act (73 FR 

23966). On May 20, 2008, we published 

a Federal Register notice (73 FR 29096) 

initiating a status review for the bald 

eagles nesting in the Sonoran Desert 

area of central Arizona. 

On February 25, 2010, the Service 

published its 12-month finding on the 

October 6, 2004, petition, as required by 

the March 5, 2008, court order (75 FR 

8601). The Service found that the bald 

eagles nesting in the Sonoran Desert 

area did not qualify as a DPS and, 

therefore, were not a listable entity 

under the Act. Concurrent with 

publication of our 12-month finding, the 

Service filed a motion for dissolution of 

the court’s injunction. Plaintiffs asked 

the Court for leave to file a 

supplemental complaint challenging the 

merits of the new 12-month finding. By 

order dated September 30, 2010, the 

court denied the Plaintiffs’ request to 

file a supplemental complaint, and 

dissolved the injunction. This had the 

effect of reinstating the provisions of the 

delisting rule for the bald eagles nesting 

in the Sonoran Desert area of central 

Arizona, thereby removing the bald 

eagles nesting in the Sonoran Desert 

area of central Arizona from the List of 

Endangered and Threatened Wildlife. 

(Center for Biological Diversity, et al. v. 

Salazar, et al., 07–cv–00038–PHX– 

MHM, 2010 U.S. Dist. LEXIS 72664 (D. 

Ariz. Sept. 30, 2010). On September 2, 

2011, the Service published a final rule 

to comply with the court’s September 

30, 2010, order. 

On October 5, 2010, CBD and the 

Maricopa Audubon Society (Plaintiffs) 

filed a new lawsuit in the U.S. District 

Court for the District of Arizona, 

challenging the Service’s February 25, 

2010, 12-month finding that the bald 

eagles nesting in the Sonoran Desert 

area did not qualify as a DPS. On 

January 5, 2011, the court granted the 

San Carlos Apache Tribe of Arizona’s 

November 24, 2010, motion to intervene 

as Intervenor-Plaintiff. On March 1, 

2011, the court granted the Salt River 

Pima-Maricopa Indian Community’s 

January 12, 2011, motion to intervene as 

Intervenor-Plaintiff. 

On November 30, 2011, the court 

granted Plaintiffs’ motions for summary 

judgment to the extent they asserted the 

Service’s 12-month finding was 

procedurally flawed. The court order 

(Center for Biological Diversity v. 

Kempthorne, CV 10–2130–PHX–DGC 

(D. Ariz)) required the Service to 

produce a new 12-month finding by 

April 20, 2012, based on information 

gathered in the status review already 

conducted. The court order also 

directed the Service to address issues 

identified in the order in the new 12- 

month finding, specifically whether the 

Service has adopted a new 

interpretation of the DPS policy and 

provide a reasoned explanation for why 

loss of the desert eagle would not result 

in a significant gap in the range 

(assuming the Service reached this 

conclusion in its new 12-month 

finding). 

Public Information 

As noted above, on May 20, 2008, the 

Service published a notice to initiate a 

12-month status review for the Sonoran 

Desert population of bald eagle in 

central Arizona and northwestern 

Mexico, and a solicitation for new 

information (73 FR 29096). To allow 

adequate time to consider the 

information, we requested that 

information be submitted on or before 

July 7, 2008. On January 15, 2009, a 

second Federal Register notice (74 FR 

2465) was published announcing the 

continuation of information collection 

for the 12-month status review. In order 

to allow us adequate time to consider 

and incorporate submitted information, 

we requested that we receive 

information on or before July 10, 2009. 

Between May 2008 and February 2010, 

we received 31 responses via http:// 

www.regulations.gov, and 5 letters by 

U.S. mail. 

Tribal Information 

In accordance with Secretarial Order 

3206, the Service acknowledges our 

responsibility to consult with federally 

recognized Tribes on a government-togovernment basis. Over the course of the 

previous bald eagle status review, we 

corresponded and met with various 

Tribes in Arizona, all of whom support 

protection of the bald eagle under the 

Act. On July 2, 2008, the Service and 

Tribal representatives from four Western 

Apache Tribes and one Nation (White 

Mountain Apache, San Carlos Apache, 

Tonto Apache Tribes, and YavapaiApache Nation) met to hear testimony 

from cultural authorities on a variety of 

subjects, including the history of the 

eagle in Arizona and the importance of 

the eagle to the Apache people. At the 

request of Tribal representatives, this 

meeting was recorded and incorporated 

into the administrative record for the 

12-month finding. On July 3, 2008, the 

Service met with members of the Salt 

River Pima-Maricopa Indian 

Community, Gila River Indian 

Community, Tohono O’Odham Nation, 

Ak-Chin Indian Community, Tonto 

Apache Tribe, Fort McDowell Yavapai 

Nation, the Hopi Tribe, Pascua Yaqui 

Tribe, Zuni Tribe, and the InterTribal 

Council of Arizona. This meeting was 

held in Phoenix, Arizona, and a court 

reporter recorded the meeting minutes. 

Members of the Tribes and nations 

present, however, did not consider this 

meeting to constitute government-togovernment consultation pursuant to 

Secretarial Order 3206. On July 20, 

2009, an official consultation meeting 

between the Service and Salt River 

Pima-Maricopa Indian Community 

occurred. Written comments were 

provided by the Western Apache Tribes 

and Nation and the Salt River PimaMaricopa Indian Community on July 10, 

2009. 

Although comments from the Native 

American communities were provided 

in writing, much of the knowledge 

about the bald eagle was offered during 

the above-referenced face-to-face 

meetings. Native American knowledge 

about the eagle is passed down orally 

from one generation to the next, which 

is often referred to in the literature as 

traditional ecological knowledge. 

Traditional ecological knowledge refers 

to the knowledge base acquired by 

indigenous and local peoples over many 

hundreds of years through direct contact 

with the environment. Traditional 

knowledge is based in the ways of life, 

belief systems, perceptions, cognitive 

processes, and other means of 

organizing and transmitting information 

in a particular culture. Traditional 

ecological knowledge includes an 

intimate and detailed knowledge of 

plants, animals, and natural 

phenomena; the development and use of 

appropriate technologies for hunting, 

fishing, trapping, agriculture, and 

forestry; and a holistic knowledge, or 

‘‘world view,’’ which parallels the 

scientific discipline of ecology (Inglis 

1993, p. vi). 

Testimony by the Western Apache 

Tribes and Nation and Salt River PimaMaricopa Indian Community clearly 

demonstrates the importance of the bald 

eagle to their culture, its relevance to 

their well-being, and their respect for its 

power. Their testimony also 

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demonstrates the Western Apache and 

Salt-River Pima Maricopa knowledge 

base of the bald eagle and its habitat. 

The Native American relationship with 

the bald eagle in the Sonoran Desert 

Area predates modern Western 

scientific knowledge of the bald eagle by 

thousands of years (Lupe et al. pers. 

comm. 2008, p. 1). Given the expertise 

and traditional ecological knowledge 

about the bald eagle in the Southwest 

demonstrated by the Western Apache 

Tribes and Nation and Salt-River Pima 

Maricopa Indian Community, we have 

incorporated this information into our 

status review and 12-month finding. 

Species Information 

The bald eagle (Haliaeetus 

leucocephalus) is the only species of sea 

eagle regularly occurring in North 

America (60 FR 35999; July 12, 1995). 

Literally translated, H. leucocephalus 

means white-headed sea eagle. Bald 

eagles are birds of prey of the Order 

Falconiformes and Family Accipitridae. 

They vary in length from 28 to 38 inches 

(in) (71 to 96 centimeters (cm)), weigh 

between 6.6 and 13.9 pounds (lbs) (3.0 

and 6.3 kilograms (kg)), and have a 66- 

to 96-in (168- to 244-cm) wingspan. 

Distinguishing features of adult bald 

eagles include a white head, tail, and 

upper- and lowertail-coverts; a darkbrown body and wings; and yellow 

irises, beak, legs, and feet. Immature 

bald eagles are mostly dark brown and 

lack a white head and tail until they 

reach approximately 5 years of age 

(Buehler 2000, p. 2). 

Biology and Distribution 

In many Western Apache groups, the 

bald eagle is called Ist5ga ́ı ́, which 

translates to ‘‘the white eagle’’ and is 

distinguished from the golden eagle, 

which is called Itsa Cho or ‘‘the big 

eagle.’’ The bald eagle was first 

described in Western culture in 1766 as 

Falco leucocephalus by Linnaeus. This 

South Carolina specimen was later 

renamed as the southern bald eagle, 

subspecies Haliaeetus leucocephalus 

leucocephalus (Linnaeus) when 

Townsend identified the northern bald 

eagle as Haliaeetus leucocephalus 

alascanus in 1897 (Buehler 2000, p. 4). 

By the time the bald eagle was listed 

throughout the lower 48 States under 

the Act in 1978, ornithologists no longer 

recognized the subspecies (American 

Ornithologists Union 1983, p. 106). 

The bald eagle ranges throughout 

much of North America, nesting on both 

coasts from Florida to Baja California, 

Mexico, in the south, and from Labrador 

to the western Aleutian Islands, Alaska, 

in the north. Fossil records indicate that 

bald eagles inhabited North America 

approximately 1 million years ago, but 

they may have been present before that 

(Stalmaster 1987, p. 5). An estimated 

quarter to a half million bald eagles 

lived on the North American continent 

before the first Europeans arrived. 

Though once considered endangered, 

the bald eagle population in the lower 

48 States has increased considerably in 

the last thirty years. Regional bald eagle 

populations in the Northwest, Great 

Lakes, Chesapeake Bay, and Florida 

have increased five-fold in the past 20 

years. Bald eagles are now repopulating 

areas throughout much of the species’ 

historical range that were unoccupied 

only a few years ago. 

The bald eagle is a bird of aquatic 

ecosystems. It frequents estuaries, large 

lakes, reservoirs, major rivers, and some 

seacoast habitats. Fish is the major 

component of its diet, but waterfowl, 

gulls, and carrion are also eaten. The 

species may also use prairies if adequate 

food is available. Bald eagles typically 

nest in trees, but have also been 

documented nesting on cliffs, on the 

ground, in mangroves, in caves, and in 

manmade structures (e.g., cell phone 

towers). Trees must be sturdy and open 

to support a nest that is often 5 feet (ft) 

(1.52 meters (m)) wide and 3 ft (0.91 m) 

deep. Adults tend to use the same 

breeding areas year after year, and often 

the same nest, though a breeding area 

may include one or more alternate nests. 

Nest shape and size vary, but typical 

nests are approximately 4.9 to 5.9 ft (1.5 

to 1.8 m) in diameter and 2.3 to 4.3 ft 

(0.7 to 1.2 m) tall (Stalmaster 1987, p. 

53). In winter, bald eagles often 

congregate at specific wintering sites 

that are generally close to open water 

and offer good perch trees and night 

roosts. 

Bald eagles are long-lived. One of the 

longest-living bald eagles known in the 

wild was reported near Haines, Alaska, 

as 28 years old (Schempf 1997, p. 150). 

In 2009, a female eagle nesting at Alamo 

Lake in Arizona turned 30 years old (J. 

Driscoll, Arizona Game and Fish 

Department (AGFD), pers. comm. 2009). 

In captivity, bald eagles may live 40 or 

more years. It is presumed that once 

they mate, the bond is long-term. 

Variations in pair bonding are known to 

occur. If one mate dies or disappears, 

the other will accept a new partner. 

Bald eagle pairs begin courtship about 

a month before egg-laying. In the 

southern portion of its range, courtship 

occurs as early as September, and in the 

northern portion of its range, as late as 

May. The nesting season lasts about 6 

months. Incubation lasts approximately 

35 days, and fledging takes place at 11 

to 12 weeks of age. Parental care may 

extend 4 to 11 weeks after fledging 

(Hunt et al. 1992, p. C9; Wood et al. 

1998, pp. 336–338). The fledgling bald 

eagle is generally dark brown except the 

underwing linings, which are primarily 

white. Between fledging and adulthood, 

the bald eagle’s appearance changes 

with feather replacement each summer. 

Young, dark bald eagles may be 

confused with the golden eagle, Aquila 

chrysaetos. The bald eagle’s distinctive 

white head and tail are not apparent 

until the bird fully matures, usually at 

4 to 5 years of age. 

The migration strategies for breeding, 

nonbreeding, and juvenile or subadult 

age classes of bald eagles will vary 

depending on geographic location. 

Young eagles may wander widely for 

years before returning to nest in natal 

areas. Northern latitude bald eagles 

winter in areas such as the Upper 

Mississippi River, Great Lakes 

shorelines, and river mouths in the 

Great Lakes area. For midcontinent bald 

eagles, wintering grounds may be the 

southern States, and for southern 

latitude bald eagles, whose nesting may 

begin in the winter months, the 

nonbreeding season foraging areas may 

be the Chesapeake Bay or Yellowstone 

National Park during the summer. 

Eagles seek wintering (nonnesting) areas 

offering an abundant and readily 

available food supply with suitable 

night roosts. Night roosts typically offer 

isolation and thermal protection from 

winds. Carrion and easily scavenged 

prey provide important sources of 

winter food in terrestrial habitats far 

from open water. 

The first major decline in the bald 

eagle population probably began in the 

mid to late 1800s. Widespread shooting 

for feathers and trophies led to 

extirpation of eagles in some areas. 

Shooting also reduced part of the bald 

eagle’s prey base. Populations of big 

game animals like bison, which were 

seasonally important to eagles as 

carrion, were severely reduced. Hunters 

also reduced the numbers of waterfowl, 

shorebirds, and small mammals. 

Ranchers used carrion treated with 

strychnine, thallium sulfate, and other 

poisons as bait to kill livestock 

predators and ultimately killed many 

eagles as well. These were the major 

factors, in addition to loss of nesting 

habitat from forest clearing and 

development, which contributed to a 

reduction in bald eagle numbers 

through the 1940s. In 1940, Congress 

passed the Bald Eagle Protection Act (16 

U.S.C. 668–668d). This law prohibits 

the take, possession, sale, purchase, 

barter, or offer to sell, purchase or 

barter, transport, export or import, of 

any bald eagle, alive or dead, including 

any part, nest, or egg, unless allowed by 

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permit (16 U.S.C. 668(a)). ‘‘Take’’ 

includes pursue, shoot, shoot at, poison, 

wound, kill, capture, trap, collect, 

molest or disturb (16 U.S.C. 668c; 50 

CFR 22.3). The Bald Eagle Protection 

Act and increased public awareness of 

the bald eagle’s status resulted in partial 

recovery or at least a slower rate of 

decline of the species in most areas of 

the country. 

In the late 1940s, the use of dichlorodiphenyltrichloroethane (DDT) and 

other organochlorine compounds 

became widespread. Initially, DDT was 

sprayed extensively along coastal and 

other wetland areas to control 

mosquitoes (Carson 1962, pp. 28–29, 

45–55). Later farmers used it as a 

general crop insecticide. As DDT 

accumulated in individual bald eagles 

from ingesting prey containing DDT and 

its metabolites, reproductive success 

plummeted. In the late 1960s and early 

1970s, it was determined that 

dichlorophenyl-dichloroethylene (DDE), 

the principal breakdown product of 

DDT, accumulated in the fatty tissues of 

adult female bald eagles. DDE impaired 

calcium release necessary for normal 

eggshell formation, resulting in thin 

shells and reproductive failure. 

In response to this decline, the 

Secretary of the Interior, on March 11, 

1967 (32 FR 4001), listed bald eagles 

south of the 40th parallel as endangered 

under the Endangered Species 

Preservation Act of 1966 (16 U.S.C. 

668aa–668cc). Bald eagles north of this 

line were not included in that action 

primarily because the Alaskan and 

Canadian populations were not 

considered endangered in 1967. On 

December 31, 1972, the Environmental 

Protection Agency banned the use of 

DDT in the United States. The following 

year, Congress passed the Endangered 

Species Act of 1973 (16 U.S.C. 1531– 

1544). 

Nationwide bald eagle surveys, 

conducted in 1973 and 1974 by the 

Service, other cooperating agencies, and 

conservation organizations, revealed 

that the eagle population throughout the 

lower 48 States was declining. The 

Service responded in 1978 by listing the 

bald eagle throughout the lower 48 

States as endangered except in 

Michigan, Minnesota, Wisconsin, 

Washington, and Oregon, where it was 

designated as threatened (43 FR 6233, 

February 14, 1978). 

Between 1990 and 2000, the bald 

eagle population had a national average 

productivity of at least one fledgling per 

nesting pair per year. As a result, the 

bald eagle’s nesting population 

increased at a rate of about eight percent 

per year during this time period. Since 

1963, when the Audubon Society 

estimated that there were 417 nesting 

pairs, bald eagle breeding in the lower 

48 States has expanded to more than 

9,789 nesting pairs (60 FR 36001, July 

12, 1995; 64 FR 36457, July 6, 1999). By 

2007, bald eagles bred in each of the 

lower 48 States, with the greatest 

number of breeding pairs occurring in 

Minnesota (1,313), Florida (1,133), 

Wisconsin (1,065), and Washington 

(848) (72 FR 37349, July 9, 2007). 

Regional bald eagle populations in the 

Northwest, Great Lakes, Chesapeake 

Bay, and Florida have increased fivefold from the late 1970s to the late 

1990s. Bald eagles are now repopulating 

areas throughout much of the species’ 

historical range that were unoccupied 

only a few years ago (64 FR 36454; July 

6, 1999). The nationwide recovery of the 

bald eagle is due in part to the reduction 

in levels of persistent organochlorine 

pesticides (such as DDT) and habitat 

protection and management actions. 

Historical and Current Status of the 

Sonoran Desert Area Population and 

Adjacent Areas 

Below we present a discussion of 

eagle presence, nesting and breeding 

productivity in the Sonoran Desert Area 

population and throughout the entirety 

of each State surrounding the Sonoran 

Desert Area population in order to 

provide context for our evaluation of 

whether the Sonoran Desert Area is a 

distinct population segment of bald 

eagles. As described above, the Sonoran 

Desert Area refers to all Sonoran Desert 

bald eagle territories within Arizona, the 

Copper Basin breeding area along the 

Colorado River just into California, and 

the territories of interior Sonora, Mexico 

that occur within the Sonoran Desert 

and adjacent transitional communities. 

Bald eagles in Baja California are not 

included in our definition of the 

Sonoran Desert Area population 

because: (1) They are associated with a 

marine, rather than inland, environment 

(see Figure 1); (2) there is no 

documentation of Baja bald eagles 

interchanging with those in the Sonoran 

Desert Area; and (3) currently extant 

nests in Baja are limited to the 

Magdalena Bay region along the coast of 

the Pacific Ocean (Arnaud et al. 2001, 

p. 136; and King 2006, p. 4), in a coastal, 

rather than inland, climate. 

Arizona 

Hunt et al. (1992, pp. A11–A12) 

summarized the earliest records from 

the literature for bald eagles in Arizona. 

Coues noted bald eagles in the vicinity 

of Fort Whipple (now Prescott) in 1866, 

and Henshaw reported bald eagles south 

of Fort Apache in 1875. Bent (1937, pp. 

321–333) reported breeding eagles at 

Fort Whipple in 1866 and on the Salt 

River Bird Reservation (since inundated 

by Roosevelt Lake) in 1911. Breeding 

eagle information was also recorded in 

1890 near Stoneman Lake by S.A. 

Mearns. Additionally, there are reports 

of bald eagles along rivers in the White 

Mountains from 1937, and reports of 

nesting bald eagles along the Salt and 

Verde Rivers as early as 1930. Hunt et 

al. (1992, pp. D41–D46, D291–D326, 

Figures D4.0–1, D5.0–1, F3, F4, and F5) 

determined from reports and personal 

communications dating back to 1866 

that historically there were 28 known 

breeding areas, 22 known and probable 

nest sites, and at least 60 unverified 

reports of possible nests/nest sites and 

unverified reports of bald eagles located 

across the State of Arizona. Many of the 

60 possible nests/nest sites reported by 

Hunt et al. (1992) could be a collection 

of nests belonging to the same breeding 

territory. These reported locations 

ranged to the boundaries of the State 

from the Grand Canyon near Lake 

Powell, to the lower Colorado River 

where it separates Arizona and 

California, to the upper San Pedro River 

near the international border with 

Mexico, and east near the boundary 

with New Mexico (Hunt et al. 1992, 

Figures D4.0–1, D5.0–1, F3, F4, and F5). 

More recent survey and monitoring 

efforts have increased our knowledge of 

bald eagle distribution in Arizona (these 

data take into account productivity for 

breeding areas throughout Arizona, and 

are not restricted to the Sonoran Desert 

population of bald eagles evaluated 

under the petition). The number of 

known breeding areas in Arizona in 

1971 was 3; the number known in 2009 

was 59. The number of bald eagle pairs 

occupying these sites increased from 3 

in 1971 to 48 in 2009. The number of 

young hatched increased from a low of 

zero in 1972 to a high of 55 in 2006 

(Driscoll et al. 2006, pp. 48–49; McCarty 

and Johnson 2009, p. 8, in draft). 

Productivity has also changed at the 

bald eagle breeding areas since the 

1970s. Between 1975 and 1984, average 

annual productivity was 0.95 young per 

occupied breeding area. Between 1987 

and 2005, average annual productivity 

was 0.78 young per occupied breeding 

area (derived from Table 7, pp. 48–50 in 

Driscoll et al. 2006). 

Hunt et al. (1992, p. A155) conclude 

that it is likely that bald eagles nested 

on rivers throughout the Southwest 

before habitat modification occurred, as 

reports on the nature of river systems 

and the assemblage of prey fishes both 

seem conducive to nesting success and 

suggest ‘‘richer and more extensive 

habitat in the lower desert’’ than would 

have been available on the Mogollon 

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Plateau, where bald eagles are known to 

have occurred historically. Recent 

reoccupation of some of these historical 

breeding areas by bald eagles lends 

credibility to these reports. We 

evaluated a subset of the Allison et al. 

(2008, pp. 17–18) data to determine the 

status of 43 breeding areas within the 

Sonoran Desert Area of Arizona and 

concluded that 16 (37 percent) were 

pioneer breeding areas, or occupied for 

the first time. An additional 27 (63 

percent) were either reoccupied, 

meaning they were known to have been 

occupied in the past, then vacated, and 

subsequently reoccupied, or are 

considered to have been existing before 

their discovery (Allison et al. 2008, pp. 

15–16). 

The Salt River Pima-Maricopa Indian 

Community states that the O’odham 

have inhabited the Sonoran Desert and 

have known eagles since ‘‘time 

immemorial’’ (Anton and Garcia-Lewis 

2009, p. 1). Although anthropologists 

debate what this means, at least one 

noted archaeologist has documented 

detailed evidence of cultural remains in 

the nearby Pinacate area that date back 

more than 40,000 years (Hayden and 

Dykinga 1988, p. XIV). A local, informal 

consensus of 10,000 years is less 

controversial (Toupal 2003, p. 11). Bald 

eagles have been documented 

historically within the culture of the 

Four Southern Tribes of Arizona, which 

includes the Salt River Pima-Maricopa 

Indian Community, Ak-Chin Indian 

Community, Gila River Indian 

Community, and Tohono O’odham 

Nation (Anton and Garcia-Lewis 2009, 

p. 2). Because eagles are considered to 

have equal or greater standing to 

humans, eagle burials were carried out 

identical to human burial practices 

(Anton and Garcia-Lewis 2009, p. 2), 

and bald eagle burials have been 

recovered from archaeological sites 

ancestral to the O’odham culture. In 

addition, eagles are extremely 

prominent in the O’odham song culture 

(Anton and Garcia-Lewis 2009, p. 2). A 

paired set of songs recorded by 

Underhill (1938, p. 109) for a Tohono 

O’odham eagle purification ceremony 

recognized the bald eagle as the ‘‘whiteheaded eagle.’’ 

More recent evidence exists to 

demonstrate the importance and use of 

bald eagles in Apache culture. 

Herrington et al. (1939, pp. 13–15) 

noted the use of eagle feathers in 

religious practices and ceremonial 

dances. The Apache Tribes have 

documented numerous artifacts that 

were collected from the Tribes at 

Cibecue and East Fork/Whiteriver on 

the White Mountain Apache 

Reservation and on the San Carlos 

Reservation between 1901 and 1945. 

These Tribes note that these artifacts 

were made, in part, with eagle feathers, 

and include hats or caps; shields; 

medicine rings, shirts, and strings; 

amulets; war bonnets; armbands; hair 

ornaments; and wooden figurines and 

crosses. The Tribes note that these 

ceremonial items are of deep historical 

and ongoing importance, such that they 

are actively pursuing their return from 

the museums to the Tribes. The 

existence of these items demonstrates 

the use of eagle feathers by the Tribes 

for at least the last 100 years (Apache 

Tribes 2009, Tabs 6–10). 

Traditional ecological knowledge 

from the Apache tribes report more 

breeding bald eagles 150 years ago than 

are present today. Specifically, tribal 

representatives note that many areas 

that were considered nesting sites on 

the San Carlos Apache Reservation such 

as Warm Springs Canyon, Black River 

Canyon, and Salt Creek Canyon no 

longer contain active bald eagle nests. 

Bald eagles are no longer found at four 

out of seven areas that have Apache 

place-names that reference bald eagles 

(Lupe et al. pers. comm. 2008, p. 4). The 

traditional ecological knowledge shared 

by the Tribes at a July 2, 2008, meeting 

indicates that historically more bald 

eagles were observed below Coolidge 

Dam and at Talkalai Lake than currently 

exist. 

Nevada 

There are few historical or current 

breeding records for the State of Nevada. 

The lone historical record describes 

bald eagles that nested in a cave on an 

island at Pyramid Lake in northwestern 

Washoe County in northwestern Nevada 

in 1866 (Service 1986, p. 7; Detrich 

1986, p. 11; S. Abele, Service, pers. 

comm. 2008a; 2008b). Over 100 years 

later, the next verified nesting record 

occurred in 1985 along Salmon Falls 

Creek in Elko County in northeastern 

Nevada near the Idaho border. More 

modern nesting records are limited to 

approximately five breeding sites 

associated with human-made water 

impoundments. Reproductive 

performance and persistence of bald 

eagle pairs in Nevada has been varied. 

No breeding has been observed at the 

Salmon Falls site since 1985. 

Colorado 

According to the Northern Bald Eagle 

Recovery Plan, bald eagles in Colorado 

historically nested in the mountainous 

regions up to 10,000 ft (3,048 m). 

Successful nesting records exist for 

nests found in southwestern and westcentral Colorado. Bald eagles were 

considered common residents in the 

1940s and 1950s in and around Rocky 

Mountain National Park (Service 1983, 

p. 12). For southwestern Colorado, there 

were no verified records of nesting bald 

eagles in the 1960s (Bailey and Niedrach 

1965 in Stahlecker and Brady 2004, p. 

2). The first confirmed record for 

southwestern Colorado occurred in 1974 

at Electra Lake (Winternitz 1998 in 

Stahlecker and Brady 2004, p. 2). In 

1974, the Colorado Division of Wildlife 

reported that only a single nesting pair 

was known (Colorado Division of 

Wildlife 2008, p. 1). However, by 1981, 

there were five known occupied bald 

eagle territories in the State of Colorado 

(Service 1983, p. 23), and from the early 

1980s to 2008, the known bald eagle 

population increased to nearly 80 

territories, of which 60 are currently 

known to be active. Concentrations of 

breeding eagles are found east of the 

Continental Divide within the South 

Platte River watershed, on the Yampa 

River, on the White River, and on the 

Colorado River. Greater than 40 

territories are monitored annually, with 

near 70 percent nest success, 1.19 young 

fledged per occupied site, and 1.72 

young fledged per successful site 

(Colorado Division of Wildlife 2008, 

p. 1). 

New Mexico 

Available information indicates there 

was no specific, first-hand information 

on bald eagles nesting anywhere in New 

Mexico prior to 1979. Unverified reports 

(Bailey 1928, p. 180; Ligon 1961, p. 75) 

suggest one or two pairs may have 

nested in southwestern New Mexico, on 

the upper Gila River and possibly the 

San Francisco River, prior to 1928. 

These second-hand reports lacked 

specifics and may have referred to other 

species (Williams 2000, p. 1). 

Since completion of the 1982 

Recovery Plan, seven bald eagle 

territories have been discovered, five in 

northern New Mexico in Colfax and Rio 

Arriba Counties and two in 

southwestern New Mexico in Sierra and 

Catron Counties. Four have been 

recently occupied, and productivity has 

been fair with young produced in at 

least 6 to 15 years, depending on the 

territory (H. Walker, New Mexico 

Department of Game and Fish, pers. 

comm. 2008). 

Southern California 

Throughout southern California, 

historical bald eagle records are known 

from the Channel Islands and mainland 

counties along the Pacific Ocean 

(Detrich 1986, pp. 9–27). Prior to 1900, 

three bald eagle territory records were 

known (Detrich 1986, pp. 10–13). From 

1900 to 1940, reports of 24 to 60 nest 

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sites existed on islands off the coast of 

California, and are believed to have 

been extirpated from the islands soon 

after 1958 (Detrich 1986, pp. 18, 24). In 

inland areas in southern California, at 

least eight bald eagle pairs were known 

from Santa Barbara, Ventura, Los 

Angeles, Orange, and San Diego 

counties between 1900 and 1940, with 

indications of presence prior to this 

timeframe (Detrich 1986, pp. 13–19). By 

1981, largely due to adverse changes to 

bald eagle habitat and the effects of the 

pesticide DDT on reproduction, no 

breeding eagles were detected on the 

southern California mainland (Detrich 

1986, pp. 32, 33, 36, 39; California 

Department of Fish and Game 2008, 

p. 2). 

Beginning in 1980, bald eagles were 

translocated to Santa Catalina Island as 

chicks or eggs from wild nests on the 

mainland, or from captive breeding. 

Pairs of bald eagles have been breeding 

on the island since 1987. In a 

subsequent relocation effort between 

1987 and 1995 in the central coast 

mountains of Monterey Bay, 66 eaglets 

were translocated and released. A 

nesting pair first formed from those 

releases in 1993, and there are currently 

three nesting pairs (California 

Department of Fish and Game 2008, pp. 

2–3). Releases of birds occurred through 

2000, with no releases conducted 

between 2002 and 2008 (Ventana 

Wildlife Society 2009, p. 1). Currently, 

there are approximately six pairs of bald 

eagles on Catalina Island, with an 

additional three pairs at Santa Cruz 

Island, and one pair at Santa Rosa 

Island. There are approximately 35 to 40 

bald eagles around the Northern 

Channel islands, and another 20 birds 

around Catalina, for a total of 

approximately 60 birds among the 

Channel Islands (A. Little, pers. comm. 

2008). 

Presently, mainland southern 

California nesting bald eagles occur at 

inland isolated manmade reservoirs. 

Bald eagle breeding sites can be found 

in northwestern San Luis Obispo 

County (San Antonio and Nacimiento 

Lakes), central Santa Barbara County 

(Lake Cachuma), southwestern San 

Bernardino County (Silverwood Lake), 

extreme eastern San Bernardino County 

near the Colorado River (Copper Basin 

Lake), southwestern Riverside County 

(Hemet and Skinner Lakes), and central 

San Diego County (Lake Henshaw) 

(AGFD 2008, California Department of 

Fish and Game 2008, pp. 2–3; Driscoll 

and Mesta in prep. 2005, p. 110; 

Ventana Wildlife Society 2008, p. 1). 

Nesting attempts at Silverwood and 

Hemet Lakes are considered sporadic 

(Service 2005, p. 110). At Skinner Lake, 

reproduction efforts in the mid-1990s 

were affected by DDT, and the nest area 

subsequently burned down (Driscoll 

and Mesta in prep. 2005; AGFD 2008). 

Nest sites in northwestern San Luis 

Obispo County appear to be very 

productive, producing eaglets in all but 

one year from 1993 to 2006 (Ventana 

Wildlife Society 2008, p. 7). For 2001 to 

2008, two or three young have fledged 

annually from the Copper Basin 

breeding area, with the exception of 

2004 when the nest was blown down 

(M. Melanson, Metropolitan Water 

District of Southern California, pers. 

comm. 2006a, 2007, 2008). The blue 

aluminum leg bands of one of the adult 

bald eagles at the Copper Basin site 

indicate that the bird likely originated 

in Arizona (M. Melanson, Metropolitan 

Water District of Southern California, 

pers. comm. 2006b). 

Utah 

Bald eagles were recorded as ‘‘more or 

less frequent’’ by Allen in 1871 (p. 164) 

in the vicinity of Ogden in northern 

Utah. Throughout Utah, there are seven 

historical records between 1875 and 

1928, with five records of nesting bald 

eagles, and two other records of 

nonbreeding bald eagle observations, all 

located between Great Salt Lake and 

Utah Lake in northern Utah. In 1967, a 

nest was found to the south in Wayne 

County at Bicknell, and in 1972, an 

additional nest was located at Joes 

Valley Reservoir in San Pete County in 

central Utah, but it has since fallen. 

Additional records from the 1970s were 

of nests along the Colorado River at 

Westwater Canyon in 1975, and at the 

head of Westwater Canyon between 

1973 and 1977. Beginning in 1983, 

nesting attempts occurred at three 

nesting territories in southeastern Utah. 

Two of the territories were along the 

Colorado River near the eastern border 

of Utah, with the third near Castle Dale 

in the center of the State (Boschen 1995, 

pp. 7–8). Three known nest sites (Cisco, 

Bitter Creek, and Castle Dale) were 

reported following survey work 

completed in 1994. These three nest 

sites produced an average of 

approximately 1.4 nestlings, with 1.05 

successfully fledged between 1983 and 

1994 (Boschen 1995, p. 103). 

Approximately 11 breeding areas were 

known, considered active, and 

monitored between 1983 and 2005 

(Darnell, Service, pers. comm. 2008). 

West Texas 

Historically, there were five nesting 

records for bald eagles in Texas, and 

they were all west of the 100th Meridian 

in Texas. Lloyd (1887, p. 189) reported 

nesting in Tom Green and Concho 

counties in 1886. Oberholser (1974, p. 

246) and Boal (2006, p. 46) reported 

eggs collected in Potter County near 

Amarillo by E.W. Gates in 1916. 

Oberholser (1974, in Service 1982, p. 8) 

additionally reported eggs collected by 

Smissen in 1890 in Scurry County south 

of Lubbock. Oberholser also reported an 

undated sight record of breeding eagles 

in Armstrong County near Amarillo. 

Kirby (pers. comm., in Service 1982) 

reported an active nest in nearby 

Wheeler County in 1938, and indicated 

it had been active for approximately 20 

years. Throughout the 1980s and early 

1990s there were no known breeding 

bald eagles in western Texas (Mabie et 

al. 1994, p. 215; Service 1982, p. 9). In 

2004 and 2005, two adult bald eagles 

and a nestling were observed at a nest 

in the southern Great Plains of the Texas 

Panhandle. One young was produced in 

2004, and two in 2005. No leg bands 

were readily observable on the adult 

eagles (Boal et al. 2006, pp. 246–247). 

Sonora, Mexico 

Bald eagle territories were first 

recorded in Sonora, Mexico, along the 

Rio Yaqui drainage in 1986 (Brown et al. 

1986, pp. 7–14). Since that time, seven 

bald eagle breeding areas have been 

verified, and they were all located in the 

Sonoran Desert Area of Sonora (Brown 

et al. 1986, pp. 7–14; Brown et al. 

1987b, pp. 1–2, 1987b, p. 279; Brown 

1988, p. 30; Brown and Olivera 1988, 

pp. 13–16; Brown et al. 1989, pp. 13– 

15; Brown et al. 1990, pp. 7, 9; Mesta 

et al. 1993, pp. 8–12; Russell and 

Monson 1998, pp. 62–63; Driscoll and 

Mesta 2005 in prep., pp. 78–90). Four of 

these bald eagle breeding areas have 

remained occupied (Driscoll and Mesta, 

in prep., pp. 78–90). However, 

reproductive performance of these nests 

has been relatively poor. Only a single 

nestling was recorded fledging in 2000 

and 2001, and no successful nests were 

observed in 1999, 2002, and 2005 

(Driscoll and Mesta in prep., p. 43). In 

2008, no occupancy was detected at 

bald eagle territories (R. Mesta, Service, 

pers. comm. 2008). A bald eagle pair 

was observed in 2009; however, the 

previously used cliff nest is gone, and 

a new nest was not confirmed. Illegal 

drug activity in the area has increased 

human presence, making survey work 

difficult to accomplish. The area is also 

affected by extensive water 

withdrawals, and drought and dam 

operations, leaving the future of this site 

uncertain (R. Mesta, Service, pers. 

comm. 2009). 

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Distinct Vertebrate Population Segment 

Analysis 

Section 3(16) of the Act defines 

‘‘species’’ to include ‘‘any species or 

subspecies of fish and wildlife or plants, 

and any distinct population segment of 

any species of vertebrate fish or wildlife 

which interbreeds when mature’’ (16 

U.S.C. 1532(16)). To interpret and 

implement the distinct vertebrate 

population segment provisions of the 

Act and congressional guidance, the 

Service and the National Marine 

Fisheries Service (now the National 

Oceanic and Atmospheric 

Administration—Fisheries Service), 

published the Policy Regarding the 

Recognition of Distinct Vertebrate 

Population Segments (DPS Policy) in 

the Federal Register on February 7, 

1996 (61 FR 4722). The DPS Policy sets 

forth a three-step process: the Policy 

requires the Service first to determine 

whether a vertebrate population is 

discrete and, if the population is 

discrete, then to determine whether the 

population is significant. Lastly, if the 

population is determined to be both 

discrete and significant, then the DPS 

Policy requires the Service to evaluate 

the conservation status of the 

population to determine whether the 

DPS falls within the Section 3(16) 

definition of an ‘‘endangered species’’ or 

‘‘threatened species.’’ 

In accordance with our DPS Policy, 

this section details our analysis of 

whether the vertebrate population 

segment under consideration for listing 

qualifies as a DPS, specifically, whether: 

(1) The population segment is discrete 

from the remainder of the species to 

which it belongs: and (2) the population 

is significant to the species to which it 

belongs. Discreteness refers to the 

ability to delineate a population 

segment from other members of a taxon 

based on either: (1) Physical, 

physiological, ecological, or behavioral 

factors; or (2) international boundaries 

that result in significant differences in 

control of exploitation, management, or 

habitat conservation status, or 

regulatory mechanisms that are 

significant in light of section 4(a)(1)(B) 

of the Act. 

Under our DPS Policy, if we have 

determined that a population segment is 

discrete under one or more of the 

discreteness conditions, we consider its 

significance to the larger taxon to which 

it belongs in light of Congressional 

guidance (see Senate Report 151, 96th 

Congress, 1st Session) that the authority 

to list DPSs be used ‘‘sparingly’’ while 

encouraging the conservation of genetic 

diversity. In carrying out this 

examination, we consider available 

scientific evidence of the population’s 

importance to the taxon to which it 

belongs. This consideration may 

include, but is not limited to, the 

following categories of information: (1) 

The persistence of the population 

segment in an ecological setting that is 

unusual or unique for the taxon; (2) 

evidence that loss of the population 

segment would result in a significant 

gap in the range of the taxon; (3) 

evidence that the population segment 

represents the only surviving natural 

occurrence of a taxon that may be more 

abundant elsewhere as an introduced 

population outside of its historical 

range; and (4) evidence that the discrete 

population segment differs markedly 

from other populations of the species in 

its genetic characteristics. 

The first step in our DPS analysis was 

to identify the boundaries of the 

potential population—that is, the areas 

where the population we are evaluating 

occurs. The petition from CBD, the 

Maricopa Audubon Society, and the 

Arizona Audubon Council requested 

listing for the ‘‘Southwestern desert 

nesting bald eagle population.’’ 

Determination of the Area for Analysis 

The March 6, 2008, court order 

directed the Service to conduct a status 

review of the ‘‘Desert bald eagle 

population.’’ The population referenced 

in the court order consists of those bald 

eagles in the Sonoran Desert of the 

Southwest that reside in central Arizona 

and northwestern Mexico. While we 

had specific information from the 

petitioner with respect to elevational 

parameters, bald eagle breeding areas, 

the Upper and Lower Sonoran Life 

Zones, and the State of Arizona, 

ambiguity remained with respect to 

where the boundaries of ‘‘central 

Arizona’’ are and which transition areas 

outside of the Upper and Lower 

Sonoran Life Zones to include. Because 

of these ambiguities and lack of a 

specific map in the petition, we were 

left to interpret them, primarily at the 

perimeters of those areas. 

In responding to the 2008 court order, 

we published a rule on May 1, 2008, 

reinstating threatened status under the 

Act to the bald eagle in the Sonoran 

Desert Area of central Arizona in eight 

Arizona counties: (1) Yavapai, Gila, 

Graham, Pinal, and Maricopa Counties 

in their entirety; and (2) southern 

Mohave County (that portion south and 

east of the centerline of Interstate 

Highway 40 and east of Arizona 

Highway 95), eastern LaPaz County (that 

portion east of the centerline of U.S. and 

Arizona Highways 95), and northern 

Yuma County (that portion east of the 

centerline of U.S. Highway 95 and north 

of the centerline of Interstate Highway 

8). We limited the reinstatement of 

threatened status to these areas because 

Sonoran Desert bald eagles were only 

listed under the Act in Arizona (and not 

in Mexico) at the time of the petition. 

Therefore, the court’s order enjoining 

our final delisting decision applied only 

to those eagles that reside in the 

Sonoran Desert of central Arizona. 

For the February 25, 2010, status 

review, we revisited the issue of where 

the population we are evaluating occurs, 

based on a more in-depth review of 

information received from the public, 

Tribes, and information in our files at 

that time. We determined that an 

appropriate delineation for the analysis 

includes all Sonoran Desert bald eagle 

territories within Arizona, the Copper 

Basin breeding area along the Colorado 

River just into California, and the 

territories of Sonora, Mexico, that occur 

within the Sonoran Desert and adjacent 

transitional communities. This 

expanded boundary was developed 

using vegetation community 

boundaries, elevation, and breeding 

bald eagle movement. This 

interpretation combines geographic 

proximity and recognized Sonoran 

Desert vegetation and transition life 

zones. We determined the transition 

areas based on our knowledge of their 

proximity to the Sonoran Desert itself, 

excluding territories more properly 

classified as montane or grassland 

habitat. Bald eagles in Baja California, 

Mexico, occur in an area where the 

Sonoran Desert vegetation community 

abuts a coastal environment. We 

excluded bald eagles in this area 

because they depend on marine 

resources rather than inland fisheries. 

We based delineation of the potential 

DPS on the best available scientific 

information, including the parameters 

provided by CBD (i.e., bald eagle 

territories, elevation, life zones, and 

transition areas), and the resulting 

expanded area for the population 

includes known bald eagle breeding 

areas within the Sonoran Desert 

vegetation community and transition 

areas, as defined by Brown (1994, pp. 

181–221), except Baja California. 

As noted above, we included Sonoran 

desert bald eagle territories in Sonora, 

Mexico, as part of the potential DPS 

because that area has the same 

vegetation and climate as the Sonoran 

Desert areas in Arizona. Bald eagles in 

Sonora use Sonoran Desert and 

transition vegetation communities as do 

bald eagles in the Sonoran Desert areas 

of Arizona and southern California. In 

addition, breeding season chronology in 

both areas appears to be similar 

(Driscoll et al. 2005 in prep., pp. 31–32), 

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occurring between December and June. 

Bald eagles in Sonora also nest in 

riparian trees and cliffs, as they do in 

Arizona (Driscoll et al. 2005 in prep., 

p. 31). 

When based strictly on vegetation or 

elevation lines, the expanded area 

where the population occurs is irregular 

and complex, and would be difficult to 

interpret. For this reason, we delineated 

the area of the population with more 

easily identifiable road, county, and 

state lines. 

Boundaries of the Potential DPS 

In analyzing the potential DPS under 

this 12-month status review, we 

considered habitat use by bald eagles 

breeding in the southwestern United 

States and Sonoran Desert areas in 

Mexico, vegetation communities in 

which breeding areas occur, and 

elevation levels at which breeding areas 

occur, as we did at the 90-day petition 

finding stage. However, we have 

reevaluated all potential areas that may 

meet the criteria described below, 

including areas considered in the 90- 

day finding. As a result, in this review, 

we did not restrict the potential DPS to 

the State of Arizona, and have instead 

expanded the area covered by our 

previous analysis so that this analysis 

includes portions of southeastern 

California along the Colorado River, 

Arizona, and Sonora, Mexico. We now 

refer to this expanded potential DPS 

area as the ‘‘Sonoran Desert Area 

population,’’ which replaces the term 

‘‘Sonoran Desert Area of central 

Arizona,’’ as described in our May 1, 

2008, Federal Register rule (73 FR 

23966) listing the Sonoran Desert bald 

eagle as threatened. 

To determine which areas should be 

included within the expanded boundary 

for the Sonoran Desert Area, we 

considered three factors: (1) The 

Sonoran Desert vegetation community 

(Brown 1994, pp. 180–221; Brown and 

Lowe 1994, map); (2) an elevational 

range for known breeding areas within 

the Sonoran Desert (excluding Baja 

California); and (3) movement patterns 

of breeding bald eagles both into and 

out of the Sonoran Desert Area. We 

included within the boundary portions 

of the Sonoran Desert, including its 

subdivisions and ‘‘transition areas.’’ 

Subdivisions of the Sonoran Desert 

include the Lower Colorado River 

Valley, Arizona Upland, Vizcaino, 

Central Gulf Coast, Plains of Sonora, 

and Magdalena (Brown 1994, pp. 190– 

221). Transition areas are those 

vegetation communities adjacent to the 

Sonoran Desert community. Brown 

(1994, p. 181) includes as transition 

areas semidesert grasslands, Sinaloan 

thornscrub, and chaparral. The majority 

of the breeding areas within the 

boundary occur in the Arizona Upland 

Subdivision of the Sonoran Desert. 

Exceptions include those breeding areas 

in the transition communities (where 14 

of 61 breeding areas are located) of 

Interior Chaparral, Plains & Great Basin 

Grassland, Semidesert Grassland, and 

Sinaloan Thornscrub (Brown 1994). 

These communities are most often 

adjacent to the Arizona Upland 

Subdivision of the Sonoran Desert, 

where bald eagles in these areas forage 

at least partially within the desertscrub. 

We also based the boundary on those 

portions of the Southwest within the 

elevational range of 984 to 5,643 ft (300 

to 1,720 m). This elevational range 

encompasses all known bald eagle 

breeding areas within the Sonoran 

Desert in the United States and Sonora, 

Mexico. Using Geographic Information 

Systems, the appropriate elevational 

ranges were overlapped with the 

Sonoran Desert vegetation community 

to determine where both criteria were 

met. 

We also considered information on 

movement of bald eagles into and out of 

the Sonoran Desert, as determined 

through banding and monitoring 

information. Specifically, we included 

within the boundary those bald eagles 

known to originate in or breed in the 

Sonoran Desert and transition areas, 

excluding Baja California. The banding 

and monitoring information used to 

determine eagles originating or breeding 

in the Sonoran Desert Area is described 

in detail below. 

Figure 1 below illustrates the 

boundary developed based on 

vegetation community, elevation, and 

breeding bald eagle movement. The 

boundary was modified from following 

strictly elevational or vegetation lines to 

follow more easily identifiable road, 

county, and state lines. 

BILLING CODE 4310–55–P 

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BILLING CODE 4310–55–C 

The northern perimeter of the 

expanded potential DPS boundary in 

Arizona is the same as the potential DPS 

boundary that we used in our May 1, 

2008, Federal Register notice (73 FR 

23966). This boundary follows the 

southern edges of Coconino and Navajo 

Counties, and portions of Apache 

County. It follows the Graham County 

line south on the east side until it 

reaches the Cochise County boundary. 

On the west, the boundary drops 

south along the Mohave-Yavapai 

boundary until it reaches Interstate 40. 

The boundary then follows Interstate 40 

west until its intersection with the State 

boundary. It continues west 5 miles (mi) 

(8 kilometers (km)) and then south along 

a line drawn 5 mi (8 km) west of and 

parallel to the Colorado River until it 

reaches Highway 2 in Sonora, Mexico. 

The southern boundary of the 

expanded potential DPS follows 

Highway 2 in Mexico east until its 

intersection with Highway 15. It follows 

Highway 15 until its intersection with 


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Highway 16. The southern boundary 

continues along Highway 16 until it 

reaches the State boundary between 

Sonora and Chihuahua. The eastern 

boundary of the expanded potential DPS 

follows the State line between Sonora 

and Chihuahua north until it reaches 

the international boundary between the 

United States and Mexico at New 

Mexico, and continues west to the State 

boundary between Arizona and New 

Mexico. The eastern boundary then 

continues north along Cochise County, 

turning slightly west along the northern 

edge of Cochise County before rejoining 

the northern perimeter. 

Bald eagles within the boundary that 

constitutes the expanded area for the 

potential DPS include those that occur 

within the appropriate vegetation 

communities and elevational range. It 

therefore includes the breeding area 

located in southeastern California, 

because it is within the Lower Colorado 

River subdivision of the Sonoran Desert. 

In addition, the bald eagles at that 

breeding area originated at the 

Horseshoe Breeding Area in Arizona. 

We have included part of Sonora, 

Mexico, within the expanded area for 

the potential DPS because bald eagles 

occur in Sonoran Desert and transitional 

communities there, as do those in 

Arizona and California. As discussed 

above, we have excluded from the 

expanded potential DPS bald eagles 

occurring in Baja California, Mexico, 

because that area is associated with a 

marine, rather than inland, 

environment. 

Arizona has additional bald eagle 

breeding areas outside of the expanded 

potential DPS boundary. These breeding 

areas include Canyon de Chelly, Luna, 

Becker, Crescent, Greer, Woods Canyon, 

and Lower Lake Mary. These breeding 

areas were excluded because they are 

not located within the Sonoran Desert. 

Discreteness 

Under the DPS Policy, a population 

segment of a vertebrate taxon may be 

considered discrete if it satisfies either 

one of the following conditions: 

(1) It is markedly separated from other 

populations of the same taxon as a 

consequence of physical, physiological, 

ecological, or behavioral factors. 

Quantitative measures of genetic or 

morphological discontinuity may 

provide evidence of this separation. 

(2) It is delimited by international 

governmental boundaries within which 

differences in control of exploitation, 

management of habitat, conservation 

status, or regulatory mechanisms exist 

that are significant in light of section 

4(a)(1)(D) of the Act. 

Banding and Monitoring Information 

Bird banding and resighting are 

important tools used to answer 

questions regarding the biology and 

movement of individual birds (U.S. 

Geological Survey 2008, p. 1). The 

techniques used on bald eagles in the 

Southwest are consistent with marking 

technique standards (Varland et al. 

2007, pp. 222–228). Within this 

analysis, we use banding and resighting 

data for bald eagles to determine if bald 

eagles in the Sonoran Desert Area are 

markedly separate from other breeding 

populations of bald eagles. Specifically, 

we use banding and resighting data to 

determine if bald eagles originating in 

areas outside the Sonoran Desert Area 

have moved into the Sonoran Desert 

Area to breed (immigration), or if bald 

eagles originating in the Sonoran Desert 

Area have moved out of the Sonoran 

Desert Area to breed (emigration). 

We used bald eagle banding and 

resighting information collected 

between 1987 and 2007 as this is the 

time period during which banding and 

resighting efforts were most thorough in 

the Southwest. Banding of bald eagle 

nestlings began prior to this time in 

Arizona, starting in approximately 1977, 

and multiple researchers contributed to 

early banding efforts (Hildebrandt and 

Ohmart 1978; Haywood and Ohmart 

1980, 1981, 1982, 1983; Grubb 1986), as 

summarized in Hunt et al. 1992 (pp. 

C181–C202). However, early banding 

efforts were opportunistic, and the 

bands used at that time were difficult to 

read without capturing birds or 

recovering dead birds. As a result, little 

resight information was gained. 

Beginning in 1987, biologists increased 

efforts to band all nestlings and 

improved the effectiveness of banding 

and resighting by using color visual 

identification bands, which are more 

easily identified (Hunt et al. 1992, pp. 

C181–C202; Driscoll et al. 2006, p. 26). 

In total, the banding and resighting 

effort for bald eagles in Arizona has 

continued for 30 years with the last 20 

years using the more informative color 

bands. 

To determine the movement of 

breeding bald eagles in our target time 

period of 1987 to 2007, we relied on 

data from two datasets. The first dataset, 

called the Bird Banding Lab (BBL) 

dataset, is derived from data collected 

and collated by the U.S. Geological 

Survey Bird Banding Laboratory (U.S. 

Geological Survey 2008). The BBL 

dataset consists of over 19,000 records 

for bald eagles throughout the species’ 

range, including those banded in the 

Southwest. The second dataset, called 

the AGFD dataset, is derived from data 

compiled and used by Allison et al. 

(2008) in a demographic analysis for 

bald eagles in Arizona. 

Because our analysis focused on 

determining whether or not there is 

immigration or emigration of bald eagles 

to and from the Sonoran Desert Area, we 

analyzed bald eagles banded as 

nestlings and resighted as adults. Using 

only those birds banded as nestlings 

ensures that the origin of the banded 

birds is known, and that young birds 

originating in other areas are not 

included in the analysis. Using only 

resight information for breeding bald 

eagles eliminates data associated with 

juvenile migrants, which would not 

contribute to the breeding population. 

Generally, age five is accepted as the age 

at which adult bald eagles breed 

throughout most of the species’ range. 

For this reason, when evaluating the 

nationwide BBL dataset, we considered 

bald eagles 5 years of age or older as 

breeding adults. However, for the AGFD 

dataset, where there are numerous 

instances of bald eagles breeding at 4 

years of age in Arizona (Allison et al. 

2008), we considered bald eagles 4 years 

of age or older as breeding adults. 

Immigration Into the Sonoran Desert 

Area 

For purposes of this analysis, 

immigration is defined as the movement 

of individuals that were banded as 

nestlings outside of the Sonoran Desert 

Area and then are subsequently 

resighted as breeding birds inside the 

Sonoran Desert Area. In our analysis of 

the likelihood of bald eagle immigration 

into the Sonoran Desert Area from areas 

in closest proximity to the Sonoran 

Desert Area, we used data from the 

AGFD and the broader BBL dataset and 

considered bald eagle banding and 

resighting information from the States in 

proximity to the Sonoran Desert Area, 

including California, Colorado, Nevada, 

New Mexico, Texas, and Utah, as well 

as birds in Arizona but outside of the 

Sonoran Desert Area (see Table 1). 

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TABLE 1—RECORDS FOR BALD EAGLES BANDED AS NESTLINGS IN AREAS OUTSIDE THE SONORAN DESERT AREA AND

RESIGHTED AS BREEDING BIRDS FROM 1987 TO 2007 

[U.S. Geological Survey 2008; K. McCarty, AGFD, pers. comm. 2009; Driscoll et al. 2006, p. 49] 

State where banded 

Number of 

nestlings 

banded in 

areas in close 

proximity to 

the Sonoran 

Desert area 

1987–2002 

Number of 

banded 

nestlings 

resighted as 

breeding birds 

1987–2007 

States where banded eagles were resighted 

Number of 

resightings in 

the Sonoran 

Desert area 

Arizona outside the Sonoran Desert Area ...... 12 0 ......................................................................... 0 

California ......................................................... 103 13 (12.6%) British Columbia, CA, WA .............................. 0 

Colorado .......................................................... 152 7 (4.6%) CO, WY .......................................................... 0 

Nevada ............................................................ 0 0 (0%) ......................................................................... 0 

New Mexico .................................................... 0 0 (0%) ......................................................................... 0 

Texas .............................................................. 64 5 (7.8%) AZ, CA, NE, NM, TX ...................................... 0 

Utah ................................................................. 6 0 (0%) UT ................................................................... 0 

Total ......................................................... 337 25 (7.4%) ......................................................................... 0 

Available data from 2008 are not as thorough, but they are consistent with the findings from the data reported. Further, the Texas bird resighted in Arizona occurs at a high-elevation nest outside of the Sonoran Desert Area. Note: We know of no banding information for birds banded in Mexico outside the Sonoran Desert Area. 

Using the AGFD dataset, Allison et al. 

(2008, p. 25) indicate that anticipated 

survival rates for fledglings to age four 

is 28 percent. It should be noted that the 

mortality rates derived by Allison et al. 

(2008, p. 4) are based on modeling; 

however, the model was based on data 

collected over a 10-year period from 

1993 to 2003. 

The information summarized in Table 

1 indicates that 337 bald eagles were 

banded as nestlings between 1987 and 

2002 (the latest year for which a banded 

cohort could reach 5 years of age by 

2007) in the areas outside of but in 

proximity to the Sonoran Desert Area. 

Applying the survival rate of 28 percent 

to the 337 bald eagles reported banded 

as nestlings in Table 1, we would 

anticipate that approximately 94 

nestlings would have survived to age 

four. Only 25 of the banded nestlings 

were resighted as breeding birds, and 

the fate of the remaining 69 nestlings is 

unknown. However, none of the 25 

banded nestlings were resighted as 

breeding birds within the Sonoran 

Desert Area (see Table 1). 

While the number of banded and 

resighted birds in Table 1 is small, given 

the intensive effort in Arizona to 

identify the origins of banded breeding 

birds, we believe some inference is 

possible suggesting that the probability 

of nestlings originating outside of the 

Sonoran Desert Area and immigrating 

into the Sonoran Desert Area to breed is 

low. 

There is no known immigration from 

the Canyon de Chelly, Lower Lake 

Mary, Becker, Woods Canyon, Crescent, 

Greer, and Luna Lake breeding areas 

located at higher elevations within 

Arizona outside of the Sonoran Desert 

Area. To date, 29 nestlings produced at 

these breeding areas have been banded. 

Twenty-five of these were banded at the 

Luna breeding area during 1994–2000, 

2002–2005, and 2007, with 22 of them 

fledging successfully (K. McCarty, 

AGFD, pers. comm. 2009). As of 2008, 

none of these banded offspring are 

known to have entered the breeding 

population of bald eagles in the Sonoran 

Desert Area (AGFD 2008a, pp. 1–2). The 

male bird at the Crescent breeding area 

is from the Luna breeding area (the 

female is unbanded) (Jacobson et al. 

2004, p. 16). Similarly, the male bird at 

the Greer breeding area is from the Luna 

breeding area, and the female is 

unbanded (McCarty and Jacobson 2008, 

p. 9). Lower Lake Mary fledged four 

young in 2005 and 2006, and the young 

were banded. The Woods Canyon and 

Greer breeding areas were first detected 

in 2008, and no young fledged that year 

from either breeding area. Six young 

have successfully fledged from Canyon 

de Chelly as of this date, none of which 

were banded (AGFD 2006, pp. 1–2; 

AGFD 2007, pp. 1–2; Jacobson et al. 

2007, pp. 16–19; AGFD 2008a, pp. 48– 

49; AGFD 2008, unpubl. data; AGFD 

2009, pp. 1–2). 

Biologists, primarily R. Mesta, 

estimate that, due to difficulty in 

accessing territories in Sonora, Mexico, 

they are able to monitor approximately 

40 to 60 percent of the known nest sites 

each year, and 20 to 30 percent of the 

known birds are observed while visiting 

these territories. Approximately 80 

percent of the birds detected have been 

examined for auxiliary markers, such as 

colored bands, and biologists believe 

that if marked bald eagles were 

occupying known territories after 1990, 

they would likely have been detected. 

However, they note that, in years in 

which surveys are conducted, breeding 

areas are visited only once and for a 

short period of time, which would make 

it easy to miss an individual eagle. They 

note that, in 1992, an adult at the Fig 

Tree breeding area had a yellow wing 

tag (potentially indicating it had 

originated in Texas or Florida) that 

could not be read, but no one has 

observed the bird since ((Driscoll and 

Mesta 2005, in prep., p. 62; R. Mesta, 

Service, pers. comm. 2008, Ortego et al. 

2009, p. 10). 

Emigration From the Sonoran Desert 

Area 

Emigration is defined here as the 

movement of individuals originating in 

the Sonoran Desert Area to areas outside 

the Sonoran Desert Area where they are 

resighted as birds of breeding age. Our 

analysis of data from the BBL dataset 

found that 41 of the 42 nestlings (97.6 

percent) banded within the Arizona 

portion of the Sonoran Desert Area were 

subsequently resighted within the 

Sonoran Desert Area. Only one eagle 

(2.4 percent) of breeding age was 

resighted outside of the Sonoran Desert 

Area, near Temecula, California (see 

Table 2). The BBL dataset shows that 

there were 371 bald eagles banded in 

Arizona between 1987 and 2007. With 

anticipated survival rates from fledgling 

to 4 years of age at 28 percent, we 

estimate that approximately 104 

nestlings should have survived to age 

four. While we know that 42 were 

resighted, the fate of the remaining 62 

birds is unknown. 

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TABLE 2—BALD EAGLES BANDED IN ARIZONA BETWEEN 1987 AND 2002 AND RECAPTURED OR RESIGHTED AS BIRDS OF

BREEDING AGE

[U.S. Geological Survey 2008] 

State 

Number of 

birds 

(percent 

recovered) 

Notes 

Within the Sonoran Desert Area: 

Arizona ................................................................................. 40 (95.2%) 

Sonora, Mexico .................................................................... 1 (2.4%) Records indicate this bird was an adult entangled in fishing 

line at El Novillo Reservoir in Sonora. There was no breeding area at the reservoir, and the bird was not subsequently 

detected at a breeding area. 

Subtotal ................................................................................ 41 (97.6%) 

Outside of the Sonoran Desert Area: 

California .............................................................................. 1 (2.4%) This bird established a breeding area in California near 

Temecula. Birds in this breeding area were not successful 

in reproducing, and the nest site subsequently burned down 

(AGFD 2008a, p. 6). 

Colorado .............................................................................. 0 (0%) 

Nevada ................................................................................. 0 (0%) 

New Mexico ......................................................................... 0 (0%) 

Oklahoma ............................................................................. 0 (0%) 

Texas ................................................................................... 0 (0%) 

Utah ..................................................................................... 0 (0%) 

Subtotal ................................................................................ 1 (2.4%) 

Total .............................................................................. 42 (100%) 

With respect to emigration, data in the 

AGFD dataset, a separate dataset from 

the BBL discussed above, illustrate the 

fate of 89 of 314 nestlings banded 

within the Sonoran Desert Area. Only 1 

of the 89 birds was documented 

breeding outside the Sonoran Desert 

Area. Fifty returned to breed in the 

Sonoran Desert Area, 1 bred 

(unsuccessfully) in California, and 38 

were known to have died before 

breeding (see Table 3) (Allison et al. 

2008, p. 19). Allison et al. (2008, p. 7) 

note that, from 1987 through 2003, 83 

percent of known fledglings in the 

Sonoran Desert Area were banded. 

Traditional ecological knowledge about 

bald eagles supports these data on 

emigration. Western Apache informants 

having expert knowledge of bald eagles 

in the Sonoran Desert Area testified that 

adult eagles do not leave Arizona. 

TABLE 3—DISPOSITION OF ARIZONA

BALD EAGLES BANDED AS

NESTLINGS FROM 1987 TO 2003 

[Allison et al. 2008, p. 19] 

Fate of nestlings Number of 

eagles 

Dead before fledging ............ 123 

Unbanded Nestlings ............. 62 

Banded Nestlings—Fate Unknown ................................ 225 

TABLE 3—DISPOSITION OF ARIZONA

BALD EAGLES BANDED AS

NESTLINGS FROM 1987 TO 2003— 

Continued 

[Allison et al. 2008, p. 19] 

Fate of nestlings Number of 

eagles 

Banded Nestlings—Fate 

Known: 

Dead before Breeding ....... 38 

Bred in Arizona ................. 50 

Bred in California .............. 1 

Total ........................... 499 

Banding and resighting efforts have 

not been as intensive in the areas in 

close proximity to the Sonoran Desert 

Area as they have been in Arizona, 

including the Sonoran Desert Area. We 

sent a questionnaire to bald eagle 

biologists in surrounding States in 2008 

in an attempt to determine the level of 

banding and monitoring efforts in some 

of these regions. In response to the 

questionnaire, we determined that 

surveys for breeding birds occur 

annually at Santa Cruz and Santa Rosa 

Islands off the coast of California, as 

well as in southern California at Lake 

Hemet. In survey efforts for these areas, 

all known territories and 100 percent of 

the known birds are visited, and no 

birds have bands or markers from 

Arizona (Hoggan 2008, pp. 1–2; P. 

Sharpe, pers. comm. 2008). 

Additionally, less-formal monitoring 

occurs in other areas in California 

through a variety of agencies and 

interested groups, including the U.S. 

Forest Service, the California 

Department of Fish and Game, the 

Ventana Wildlife Society, and the 

Channel Islands Live! Web site with 

similar results (i.e., no birds with bands 

from Arizona have been reported). In 

addition, sites known to support 

breeding pairs, such as the Copper Basin 

site, are monitored regularly. 

Six New Mexico territories have been 

monitored closely since their discovery 

in 1979, with no bands or markers from 

Arizona observed (S. Williams, pers. 

comm. 2008). Since 1974, the Colorado 

Division of Wildlife has monitored 

nesting activity; State personnel 

currently monitor approximately 40 of 

their 80 nests each year and band 

eaglets at approximately one-third of 

those nests (Colorado Division of 

Wildlife 2008, p. 1). No bands or 

markers from Arizona were observed. 

We have received no data for Utah or 

Nevada. Information on bald eagles 

banded within Arizona but outside the 

Sonoran Desert Area is summarized 

above under the ‘‘Immigration into the 

Sonoran Desert Area’’ discussion above. 

The data from areas in close 

proximity to the Sonoran Desert Area 

are not as thorough as those collected in 

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Arizona, including in the Sonoran 

Desert Area. However, the banding and 

monitoring effort for breeding bald 

eagles in Arizona over a 30-year period 

has revealed only one breeding bird to 

date that immigrated into Arizona (Luna 

Lake, outside the Sonoran Desert Area). 

We anticipate that, if immigration is 

occurring at such a low level, the same 

could be true of emigration as there are 

no known barriers that would favor 

emigration over immigration. 

Conclusion on Banding Data 

We find that the data on banding and 

resighting, while not extensive for areas 

in proximity to the Sonoran Desert Area, 

are collectively sufficient to document 

that bald eagles in the Sonoran Desert 

Area experience limited or rare 

reproductive interchange with bald 

eagles outside the Sonoran Desert Area. 

Bald eagle banding and resighting 

studies have been ongoing for greater 

than 30 years in Arizona, with the last 

20 years using the more informative 

color bands. As reported in the BBL 

dataset, of the 79 nestlings banded in 

Arizona and later resighted, 1 emigrated 

to California, outside of the Sonoran 

Desert Area, and never successfully 

reproduced. This finding indicates that 

97.6 percent of the bald eagles banded 

and resighted as breeding birds 

originated and returned to breed in the 

Sonoran Desert Area, with only 2.4 

percent (one bird) of breeding birds 

resighted in other areas (Table 2). 

Similarly, the AGFD dataset indicates 

that, for the nestlings banded between 

1987 and 2003 in areas outside of but 

in close proximity to the Sonoran Desert 

Area and resighted as breeding birds, 

none have immigrated to breed in the 

Sonoran Desert Area. 

While it is not possible to band and 

resight all bald eagles as breeding birds, 

the information provided suggests that 

the majority of breeding bald eagles 

within the Sonoran Desert Area 

population originated in the Sonoran 

Desert Area population, and have not 

been known to emigrate elsewhere to 

become part of a breeding population. 

Data have been collected over a 

substantial time period under this effort, 

during which only one instance of a 

possible immigration and only one 

instance of emigration have been 

observed within the Sonoran Desert 

Area. We believe it is reasonable to 

conclude that in rare instances, 

immigration or emigration of an 

occasional bald eagle may occur; 

however, we consider the results from 

this 20-year period sufficient to 

document a marked separation of 

breeding populations. Our DPS Policy 

does not require complete isolation, and 

allows for some limited interchange 

among population segments considered 

to be discrete (61 FR 4722; February 7, 

1996). Based on the results of these 

banding and resighting data in Arizona 

and in neighboring States, we conclude 

that the Sonoran Desert Area bald eagles 

are not interbreeding with other 

populations, although some intermixing 

may occur at a very small rate. We 

conclude that the best scientific data 

available indicates a marked separation 

of Sonoran Desert Area bald eagles from 

bald eagles outside of the Sonoran 

Desert Area. 

Natal Dispersal and Fidelity 

Bald eagles are known to return close 

to their place of birth to breed 

(Stalmaster 1987, p. 41). To illustrate 

the potential for breeding bird exchange 

between populations, the Service 

examined the records of bald eagles that 

were banded as nestlings and recovered 

5 or more years later at breeding age. We 

analyzed data associated with the eagles 

in the lower 48 States to derive a 

median dispersal distance of 43 mi (69 

km) from their natal site to their 

breeding area. Known nesting sites were 

then buffered by 43 mi (69 km) to 

determine the amount of breeding bird 

exchange that typically occurs (Service 

2008, pp. 17–18). Based on this analysis, 

Sonoran Desert Area bald eagles in the 

United States are separated from other 

southwestern populations by distances 

exceeding the median dispersal distance 

of 43 mi (69 km) for the species. The 

higher-elevation breeding areas in 

Arizona are an exception to this 

separation, as they are less than 43 mi 

(69 km) from Sonoran Desert Area bald 

eagles; however, we believe these birds 

to be reproductively and markedly 

separate from Sonoran Desert Area bald 

eagles, as described in the discussions 

on immigration above, because no 

banded offspring from these higherelevation areas have been known to 

enter the breeding population of bald 

eagles in the Sonoran Desert Area. 

Observations of actual dispersal 

behavior support the same conclusion 

as that derived from the modeling 

exercise discussed above. Hunt et al. 

(1992, p. A144) surveyed biologists 

studying nine bald eagle populations 

throughout North America, consisting of 

more than 2,000 breeding pairs of bald 

eagles. Of those breeding pairs, only two 

adults were observed to breed outside of 

their natal area. Mabie et al. (1994, p. 

218) similarly concluded through their 

study in Texas and the Greater 

Yellowstone ecosystem that bald eagles 

tend to breed near their natal area. 

Gerrard et al. (1992, pp. 159, 164) 

observed four marked adults in 

Saskatchewan, Canada, and determined 

that they bred within 15.5 mi (25 km) 

of their natal territory. 

Natal dispersal patterns for Sonoran 

Desert Area bald eagles are similar to 

those in the studies discussed above. 

Data from 21 female and 35 male bald 

eagles in Arizona indicate that adult 

females dispersed an average of 68.1 mi 

(109.7 km) from their natal areas, while 

males dispersed an average of 28.0 mi 

(45.1 km) from their natal areas to breed 

(Allison et al. 2008, p. 30), but remained 

within the Sonoran Desert Area. 

This information about natal dispersal 

patterns supports our conclusion above, 

based on the banding and monitoring 

data, that there is a marked separation 

of Sonoran Desert Area bald eagles from 

bald eagles outside of the Sonoran 

Desert Area. 

Lack of Population Sources 

The immigration of adult bald eagles 

into the Sonoran Desert Area population 

from populations in relatively close 

proximity to the Sonoran Desert Area is 

likely limited by small population sizes 

in surrounding States, and their 

separation from the Sonoran Desert Area 

by long distances, over unoccupied 

habitats. There are currently eight 

known breeding areas in southern 

California in addition to populations on 

Santa Cruz and Santa Rosa Islands off 

the coast of California (California 

Department of Fish and Game 2008, pp. 

2–3; Ventana Wildlife Society 2008, p. 

1). Colorado has a somewhat larger 

population, with approximately 80 

active breeding areas (Colorado Division 

of Wildlife 2008, p. 1). Nevada has 

approximately one inactive and five 

active breeding territories. Two 

territories, Carson River and Lahontan 

Reservoir, last had eagles detected in 

2002 and 2006, respectively. The 

occupancy of two others is not yet 

confirmed. The remaining breeding area 

produced only two young from 1996 to 

2007 (K. Kritz, Service, pers. comm. 

2008). Utah has approximately 10 active 

territories and one inactive breeding 

territory (N. Darnall, Service, pers. 

comm. 2008). For New Mexico, the 

population of bald eagles consists of 

four currently occupied territories (H. 

Walker, NMDGF, pers. comm. 2009). 

West Texas currently has one active 

breeding territory west of the 100th 

Meridian. This territory has been active 

since 1994 (C. Boal, pers. comm. 2009). 

Marked Separation as a Consequence of 

Ecological Factors 

A final factor markedly separating 

Sonoran Desert Area bald eagles is the 

unsuitability of habitat in areas 

surrounding the Sonoran Desert Area for 

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occupancy by breeding birds. The 

majority of the bald eagle population in 

the Sonoran Desert Area occurs in 

central Arizona within the riparian 

areas of the Sonoran Desert as described 

in Brown (1994, pp. 180–221) and 

adjacent vegetation communities. 

Across the western United States, there 

are large geographic areas where 

breeding bald eagles are rarely found. 

These areas are associated with the 

Great Basin and Mohave Deserts, 

indicating that conditions in these 

desert biotic communities are not 

suitable for occupancy. In contrast, the 

Sonoran Desert and its subdivisions, 

where nesting bald eagles within the 

Sonoran Desert Area are located, are 

suitable for breeding areas because of 

the availability of water, prey, and trees 

suitable for nesting and perching. The 

Sonoran Desert scrub vegetation 

community is unique from other desert 

scrub formations in North America in its 

tropical and subtropical influences. 

Within the community, the riparian or 

riverine habitat occupied by breeding 

bald eagles is limited to areas where 

there is sufficient winter precipitation to 

support vegetation along streams 

(Brown 1994, p. 269). 

Western Apache traditional ecological 

knowledge corroborates these data 

regarding bald eagles within the 

Sonoran Desert Area being ecologically 

separated from other populations. Three 

Apache place names use the term Itsa 

Bigow (‘‘bald eagle’s home’’). Apaches 

use the term gowa (meaning ‘‘home’’) 

referring to the eagle’s entire habitat, as 

opposed to the term bit’oh (‘‘its nest’’). 

According to Basso (1996), the Western 

Apaches’ perception of the land works 

in specific ways to influence Apaches’ 

awareness of themselves. The process of 

‘‘place naming’’ documents where and 

how Apaches learned about the 

environment and how they incorporated 

these names into social and 

environmental ethics (Basso 1996). This 

concept is further exemplified by the 

Apache word ‘‘ni’’; this expression 

translates to mean both ‘‘mind’’ and 

‘‘land,’’ and thus the two words cannot 

be separated (Chairman Ronnie Lupe, 

pers. comm., 2008). The Apache bald 

eagle place names evoke an entire area 

or ecosystem of which the bald eagle is 

an intrinsic part. The place names 

include entire mountainsides composed 

of chaparral, pinyon-juniper woodland, 

and ponderosa pine forests, always in 

proximity to water (i.e., riparian areas) 

(Lupe et al. pers. comm. 2008). 

Bald eagles, including those in the 

Sonoran Desert Area, typically nest 

within 1 mi (1.6 km) of water. Bald 

eagles require cliff ledges, rock 

pinnacles, or large trees or snags in 

which to construct nests (Driscoll et al. 

2006, pp. 19–20). Those areas most 

immediately surrounding the Sonoran 

Desert Area fall within the Great Basin 

and Mohave Deserts, which contain no 

known breeding eagles or suitable 

habitat. These areas lack the appropriate 

bald eagle habitat parameters of water, 

fish, and nesting areas. Nonbreeding 

bald eagles from other populations 

would have to migrate through these 

areas to reach the Sonoran Desert Area. 

Therefore, we believe these desert areas 

result in a discontinuity of distribution 

of breeding birds, rather than as a 

barrier to dispersal, and serve to further 

isolate Sonoran Desert Area bald eagles 

from those in other populations. 

Bald eagles nesting at high elevation 

in Arizona in areas in proximity to the 

Sonoran Desert Area occupy Petran 

Montane Conifer Forest and Plains, and 

Great Basin Grassland above the 

Mogollon Rim (Brown and Lowe 1994, 

map). These eagles are not believed to 

have originated from within the 

Sonoran Desert Area, as described 

above. Similarly, bald eagles occupying 

these areas are not known to have 

occupied Sonoran Desert habitat within 

the Sonoran Desert Area. These highelevation areas appear to be unsuitable 

to Sonoran Desert Area bald eagles, as 

indicated by the lack of emigration to 

these areas by eagles originating in the 

Sonoran Desert Area. 

Conclusion on Discreteness 

Based on the available information in 

the petition, scientific literature, 

traditional ecological knowledge, and 

information in our files at the time of 

the February 25, 2010, finding, we have 

determined that the Sonoran Desert 

Area population of bald eagles is 

markedly separate from other 

populations of the species due to a lack 

of immigration to, and emigration from, 

surrounding bald eagle populations, and 

the fact that the areas immediately 

surrounding the Sonoran Desert Area 

lack the appropriate bald eagle habitat 

parameters of water, fish, and nesting 

areas and contain no known breeding 

bald eagles. Therefore, we have 

determined that the Sonoran Desert 

Area population meets the requirements 

of our DPS Policy for discreteness. 

Banding studies and resighting efforts 

demonstrate that breeding bald eagles in 

the Sonoran Desert Area are largely 

geographically separate from those in 

surrounding areas. Limited source 

populations and unsuitable habitat in 

surrounding areas further separate bald 

eagles in the Sonoran Desert Area from 

those in other areas. Although not 

absolute, we believe this separation to 

be marked, and to meet the intent of the 

DPS Policy for discreteness. 

Significance 

Since we have determined that the 

bald eagles in the Sonoran Desert Area 

meet the discreteness element of the 

DPS Policy, we now consider the 

population’s biological and ecological 

significance based on ‘‘the available 

scientific evidence of the discrete 

population segment’s importance to the 

taxon to which it belongs’’ (DPS Policy, 

61 FR at 4725). We make this evaluation 

in light of congressional guidance that 

the Service’s authority to list DPSs be 

used ‘‘sparingly’’ while encouraging the 

conservation of genetic diversity (DPS 

Policy, 61 FR at 4722; S. Rep. No. 96– 

151 (1979)). The DPS Policy describes 

four classes of information, or 

considerations, to take into account in 

evaluating a population segment’s 

biological and ecological importance to 

the taxon to which it belongs. As precise 

circumstances are likely to vary 

considerably from case to case, the DPS 

Policy does not state that these are the 

only classes of information that might 

factor into a determination of the 

biological and ecological importance of 

a discrete population. 

As specified in the DPS Policy (DPS 

Policy, 61 FR at 4722), consideration of 

the population segment’s significance 

may include, but is not limited to, the 

following classes of information: 

(1) Persistence of the population 

segment in an ecological setting that is 

unusual or unique for the taxon; 

(2) evidence that loss of the 

population segment would result in a 

significant gap in the range of the taxon; 

(3) evidence that the population 

segment represents the only surviving 

natural occurrence of a taxon that may 

be more abundant elsewhere as an 

introduced population outside of its 

historic range; and 

(4) evidence that the discrete 

population segment differs markedly 

from other populations of the species in 

its genetic characteristics. 

Significance of the discrete 

population segment is not necessarily 

determined by existence of one of these 

classes of information standing alone. 

Rather, information analyzed under 

these considerations is evaluated 

relative to the biological or ecological 

importance of the discrete population to 

the taxon as a whole. Accordingly, all 

relevant and available biological and 

ecological information is analyzed for 

importance to the taxon as a whole. 

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Persistence of the Population Segment 

in an Unusual or Unique Ecological 

Setting 

Under the DPS Policy the first 

consideration in determining whether a 

population is significant to the taxon to 

which it belongs is ‘‘persistence of the 

population segment in an ecological 

setting unusual or unique for the 

taxon.’’ Bald eagles are highly 

adaptable, wide-ranging habitat 

generalists. Across the range of the 

species, there is no ‘‘usual’’ ecological 

setting, in terms of the elevation, 

temperature, prey species, nest tree 

species, or type of water source, for the 

taxon. The bald eagle is capable of 

inhabiting areas throughout North 

America, so long as a sufficient food 

source persists. This contrasts with a 

situation where a portion of the range of 

a particular species exhibits one set of 

similar habitat characteristics but the 

distinct population segment utilizes a 

different set of habitat characteristics. 

For bald eagles, there are many options 

for suitable habitat. Though the Sonoran 

Desert Area may represent a unique set 

of habitat characteristics, we cannot say 

it is unusual or unique for the bald eagle 

such that persistence there is significant 

to the bald eagle as a whole. 

In order to address the court’s 

September 30, 2011, order, we reviewed 

previous DPS determinations that 

described the Service’s analysis of 

whether the population’s persistence in 

an unusual or unique ecological setting 

was significant to the taxon as a whole. 

A number of DPS determinations 

provided little detail—either regarding 

which of the four considerations 

identified in the DPS Policy had formed 

the basis for the determination, or 

regarding how the Service had analyzed 

the ‘‘unusual or unique ecological 

setting’’ consideration; this tended to be 

the case with determinations that were 

completed in the ensuing years after the 

DPS Policy was adopted. Subsequently, 

as the determinations provided more 

detail about the significance analysis, 

the analyses of ‘‘unusual or unique 

ecological setting’’ began to include 

discussions not only of whether there 

were any unusual habitat 

characteristics, but also of whether 

persistence among those habitat 

characteristics was unusual or unique 

for the taxon and made that population 

significant to the taxon as a whole. 

Elements that the Service often 

considered in these analyses included: 

(1) The extent to which there was 

evidence of adaptations—whether direct 

evidence of physical changes or indirect 

evidence of changes in life-history 

traits—that could be significant to the 

conservation of the taxon as a whole; 

and (2) the extent to which the taxon 

was a habitat generalist that could adapt 

to diverse ecological settings. In 

addition to those elements, we also 

considered the extent to which other 

populations of the species could or 

could not persist in the particular 

ecological setting such that the 

persistence of this population in that 

setting is biologically or ecologically 

important to the taxon as a whole. 

Consideration of these elements has 

been incorporated in the way the 

Service has interpreted ‘‘persistence in 

an ecological setting unusual or unique 

for the taxon’’ under the DPS Policy in 

previous DPS determinations. 

General information about the biology 

and life history of the bald eagle can be 

found in the Species Information 

section above. The bald eagle is able to 

occupy a broad range of vegetation 

communities and ecosystems 

throughout North America. The bald 

eagle is distributed across the North 

American continent (stretching from the 

Aleutian Islands to Baja California, 

Mexico, and from northeastern Canada 

to Florida). The bald eagle breeds at 

elevations ranging from sea level to 

mountains as high as 10,000 feet. It also 

occupies a range of aridity; the bald 

eagle is known to live in some of the 

driest areas in the United States and in 

some of the wettest. 

Bald eagles occur throughout North 

America wherever there is a sufficient 

source of prey. Habitat structure and 

proximity to a sufficient food source are 

usually the primary factors that 

determine suitability of an area for 

nesting (Grier and Guinn, p. 44). Nesting 

generally occurs along rivers, lakes, and 

seacoasts in proximity to a sufficient 

source of prey. Bald eagles primarily eat 

fish, but they will also eat amphibians, 

reptiles, other birds, small mammals, 

and carrion (dead animals) including 

carcasses of large mammals (e.g., cows, 

elk, deer). Bald eagles typically nest in 

trees, but have also been documented 

nesting on cliffs, on the ground, in 

mangroves, in caves, and in manmade 

structures (e.g., cell phone towers). Bald 

eagles are not limited to nesting in or 

near any particular species of tree, nor 

are they limited to eating any particular 

species or even class of prey. 

The bald eagle has also been shown 

to be highly adaptable to changes in the 

landscape. Data suggest that eagles 

across many parts of their range are 

demonstrating a growing tolerance of 

human activities in proximity to nesting 

and foraging habitats. Eagles in these 

situations continue to successfully 

reproduce in settings previously 

considered unsuitable. For example, in 

Florida, some bald eagle pairs have 

shown adaptation to human presence by 

nesting in residential subdivisions and 

commercial and industrial parks, and on 

cell phone towers and electric 

distribution poles. A common thread 

throughout these urban and suburban 

landscapes is the availability of ample 

food sources such as natural lakes, 

rivers, and ponds; artificial stormwater 

retention ponds; and public landfills 

(Millsap et al. 2002, p. 10). In light of 

this success in diverse habitats, the bald 

eagle appears to be highly adaptable to 

a variety of habitat conditions based on 

food availability. 

According to Hunt et al. (1992, p. 

A163) and Glinski (1998, p. 52), bald 

eagle nesting habitats in Arizona are 

among the most unusual nesting 

habitats occupied by the species, with 

many of the nests located in open desert 

under conditions of high heat and low 

humidity. On its face, this suggests that 

the Sonoran Desert Area is an ecological 

setting that is unusual or unique for the 

species. However, as discussed above, 

we must assess persistence in this 

unique or unusual ecological setting in 

terms of the biological or ecological 

importance of the population’s 

persistence to the species as a whole. 

Consistent with previous DPS 

determinations, we took into account 

the ‘‘unusual or unique ecological 

setting’’ consideration by first 

evaluating whether there was any 

evidence of adaptations—whether direct 

evidence of physical changes or indirect 

evidence of changes in life-history 

traits—that could be significant to the 

conservation of the taxon as a whole. 

The DPS Policy does not require 

evidence of adaptation to a unique or 

unusual ecological setting in order to 

make a finding of significance; however, 

direct evidence of adaptation to an 

ecological setting could be a strong 

indication that persistence of the 

population segment in that ecological 

setting is significant to the taxon as a 

whole. The ecological setting of the 

Sonoran Desert is characterized by hot 

and dry summers. We examined a 

number of characteristics of bald eagles 

in the Sonoran Desert Area to determine 

if there was any direct or indirect 

evidence of adaptations to that 

ecological setting such that persistence 

of that population is significant (i.e., 

biologically or ecologically important) 

to the bald eagle as a whole. For 

example, we evaluated whether it is 

significant to the bald eagle as a whole 

that individuals in the Sonoran Desert 

Area population are possibly smaller 

than those in other populations or that 

the egg shell porosity for the Sonoran 

Desert Area population differs from egg 

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shell porosity for other populations. In 

addition, we evaluated whether there 

may have been changes in timing of 

breeding, specialized feeding on desert 

fish, cliff nesting, or juvenile migration 

characteristics that make persistence of 

the population in the Sonoran Desert 

Area significant to the taxon. 

Bald eagles in the Sonoran Desert 

Area are smaller in size than many other 

bald eagles. One theory presented for 

this difference is that the smaller size 

indicates an adaptation to the hotter, 

drier Sonoran Desert environment. In 

fact, Hunt et al. (1992, p. A165) suggest 

that the smaller size of Arizona bald 

eagles was significant enough that the 

introduction of foreign genes into the 

population might disrupt coadapted 

gene complexes (a group of genetic traits 

that have high fitness when they occur 

together, but which without each other 

have low fitness) specific to the 

population. 

However, we have found general 

differences in the size of bald eagles in 

the northern latitudes and birds in the 

southern latitudes. For instance, 

Stalmaster (1987, pp. 16–17) notes that 

northern eagles are much larger and 

heavier than their southern 

counterparts. This is consistent with 

Bergmann’s Rule, which holds that 

animal size increases with increasing 

latitude due to changes in climate. 

Consistent with this rule, Hunt et al. 

(1992, pp. A158–A161) report that bald 

eagles in Arizona are smaller than those 

in Alaska and the Greater Yellowstone 

Region. Supporting this conclusion, 

Gerrard and Bortolotti (1988, p. 14) note 

that bald eagles in Florida, which is 

farther south than Arizona, are the 

smallest, with a gradation of large to 

small from north to south within the 

Florida populations. This information 

suggests that small size is not an 

adaptation unique to the Sonoran Desert 

but is rather part of the natural 

variability of the taxon as a whole. 

Another theory presented of possible 

adaptation from the taxon as a whole is 

the possible differences in egg shell 

porosity of Arizona bald eagles from 

bald eagles in other parts of the range 

of the species. Hunt et al. (1992) discuss 

pores in eggshells of bald eagles in 

Arizona. Hunt et al. (1992) note that the 

pores of the eggs assessed are one to two 

orders of magnitude smaller than those 

in California bald eagle eggs. Some of 

the public comments received during 

the public comment period for our prior 

status review questioned whether or not 

these pores may have an effect on water 

loss from bald eagle eggs in the arid 

environment. 

However, Hunt et al. (1992) did not 

reach any conclusions as to the 

significance this difference in egg shell 

porosity may have to Arizona eagles. No 

other reported studies analyzed the 

potential significance of this finding. 

Furthermore, the Hunt et al. (1992) 

study consisted of an extremely small 

sample size of only four eggs. Given the 

small sample size of this study, and the 

lack of analysis in the study, it would 

not be scientifically robust to draw any 

conclusions from the Hunt et al. (1992) 

study. As a result, we do not consider 

the potential difference of egg shell 

porosity to be evidence of adaption to 

the Sonoran Desert. 

Therefore, based on our review of 

information as it relates to body size and 

eggshell porosity, it does not appear that 

there is direct evidence of an adaptation 

of the bald eagle to the Sonoran Desert 

Area. Additionally, we did not find any 

evidence of other traits or factors that 

would indicate evidence of an 

adaptation to the Sonoran Desert Area. 

Next we discuss differences in lifehistory traits that may be an indirect 

indication of an adaptation to the 

Sonoran Desert Area that could indicate 

the population’s persistence there is 

significant to the taxon as a whole. The 

life-history traits may include timing of 

breeding, feeding habits, nest site 

selection, and juvenile migration. 

We assessed whether bald eagles in 

the Sonoran Desert Area breed earlier 

than many other bald eagles, a change 

in life history trait that could indicate 

there has been an adaptation to the 

Sonoran Desert Area setting such that 

persistence there is significant to the 

taxon as a whole. As discussed in the 

Species Information section above, bald 

eagle pairs begin courtship about a 

month before egg-laying. In the south, 

courtship occurs as early as September, 

and in the north, as late as May. The 

nesting season lasts about 6 months. 

However, as with bald eagle size 

variation, a general examination by 

latitude reveals differences between 

bald eagles in northern and southern 

regions. Timing of various breeding 

events in bald eagles is tied to the 

latitude of the nesting area, with eagles 

at more northern latitudes breeding at 

later dates (Stalmaster 1987, p. 63). 

Gerrard and Bortolotti (1988, p. 76) note 

that bald eagles in Florida lay eggs from 

early November to mid-December. 

Henry et al. (1993, p. 208) report that 

Baja California bald eagles are already 

incubating by mid January, which 

indicates a mid-December to earlyJanuary egg-laying period. In Louisiana, 

bald eagles lay eggs between October 

and mid-March, but most clutches are 

complete by late December (Service 

1989). 

The timing of breeding chronology for 

the bald eagles in the Sonoran Desert 

Area is consistent with this latitudinal 

variation. Specifically, the breeding 

chronology of Florida birds (further 

south than the Sonoran Desert Area 

eagles) is even earlier than those in the 

Sonoran Desert Area. Therefore, we find 

it unlikely that the breeding chronology 

of bald eagles in the Sonoran Desert 

Area is a life-history trait that is 

biologically or ecologically important to 

the species as a whole. 

We assessed whether there was 

evidence that bald eagles in the Sonoran 

Desert Area specialized on desert fishes. 

The most common fishes eaten by bald 

eagles in Arizona are: Sonora 

(Catostomus clarki) and desert suckers 

(Catostomus insignis); channel 

(Ictalurus punctatus) and flathead 

catfish (Pylodictis olivaris); common 

carp (Cyprinus carpio); largemouth 

(Micropterus salmoides), smallmouth 

(Micropterus dolomieui), yellow 

(Morone mississippiensis), and white 

bass (Morone chrysops); and black 

crappie (Pomoxis nigromaculatus) 

(Service 1982, p. 11; Driscoll et al. 2006, 

p. 6). However, although bald eagles are 

opportunistic feeders whose diet is 

mostly made up of fish, they will eat 

birds, amphibians, reptiles, small 

mammals, and carrion. Specifically, a 

study found that the diet of eagles in 

Arizona based on prey remains 

contained 76 percent fish, 14 percent 

mammals, and 10 percent birds (Hunt et 

al. 2002, p. 249). The same study found 

that of 10 breeding areas where prey 

remains were analyzed, suckers were 

the most common prey in only three 

breeding areas (Hunt et al. 2002, p. 250). 

Suckers often spawn in riffles, the 

shallowest of the riverine habitats, and 

may be consistently exposed to attack at 

this stage of their life cycle (Minckley 

1973, pp. 162, 169; Hunt et al. 1992, p. 

A57). Water temperature is the catalyst 

for fish spawning and, therefore, also 

causes differences in timing of fish 

availability within breeding areas. When 

suckers (who spawn early) and carp or 

catfish (who spawn later) are common, 

the result may be a prolonged 

availability of food for eagles (Hunt et 

al. 1992, p. A70). Suckers are the first 

of essential species to become most 

available to eagles while they are 

incubating eggs or feeding small young. 

The movement of carp into shallow 

water to forage generally occurs 

seasonally after suckers have finished 

spawning (Hunt et al. 1992, p. A70). 

Because an eagle’s foraging time is 

reduced due to the necessity of 

incubation or the care of newly hatched 

nestlings unable to regulate their own 

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body temperature, the sucker’s place in 

the sequencing of available prey may be 

of added importance for successful 

reproduction for eagles relying on freeflowing and regulated streams. 

Additionally, there are no other fish 

species used by bald eagles within the 

Sonoran Desert Area along rivers that 

have the same spawning schedule and 

accessibility to nesting eagles. Although 

native Sonoran and desert suckers seem 

to be important to bald eagles in the 

Sonoran Desert Area, not only for how 

they become available, but also for 

when they become available, there are 

no data to suggest that bald eagles 

specialize on suckers or that foraging on 

suckers is the result of a unique 

adaptation to the desert environment 

that is biologically or ecologically 

important to the species as a whole. 

We considered whether cliff nesting is 

an adaptation to the conditions in the 

Sonoran Desert Area that indicates that 

this population’s persistence there is 

biologically or ecologically important to 

the taxon as a whole. Hunt et al. (1992, 

p. A-ii) report that, in the Sonoran 

Desert Area, when both tree and cliff 

nests were available, eagles 

nonrandomly chose cliffs rather than 

trees, indicating that Sonoran Desert 

Area bald eagles may have a preference 

for cliff nests. 

Stalmaster (1987, p. 121) noted that 

cliff nesting is common in Arizona, but 

he also noted that exceptions to tree 

nests occur in other areas. Gerrard and 

Bortolotti (1988, p. 41) note that bald 

eagles in other areas may nest on cliffs 

if suitable trees are not available. This 

is supported by Buehler (2000), who 

states that bald eagles use ground nests 

(a category in which he includes nests 

built on cliff sides) in treeless regions 

such as Alaska, north Canada, islands 

off the coast of California, and Arizona. 

Bald eagles are also known to nest on 

cliffs on the Channel Islands off 

California (NOAA 2006). Bald eagles in 

areas of Alaska where there are no 

suitable nest trees also are known to 

nest on cliffs, sea stacks, hillsides, and 

rock promontories (Sherrod et al. 1976, 

p. 153). It is likely that up to 10 percent 

of the bald eagles in Alaska nest on the 

ground (Schempf pers. comm. 2007). 

Additionally, ground nesting has also 

been documented in limited situations 

in northwestern Minnesota and Florida 

(Hines and Lipke 1991, pp. 155–157; 

Shea et al. 1979, pp. 3–5). Eagles can 

also nest in a variety of unconventional 

situations, such as utility poles, 

abandoned heavy equipment, 

mangroves, cacti (in Baja), and root 

wads washed up on sandbars. 

Additionally, bald eagles, across their 

range, will use whatever high nest sites 

are available near the aquatic areas they 

inhabit. In the Sonoran Desert Area 

these sites often happen to be cliffs, but 

eagles in the Sonoran Desert Area have 

also nested in cottonwood, willow, 

sycamore, pinyon pine, and ponderosa 

pine trees. Many Sonoran Desert Area 

eagle pairs have built and used both tree 

and cliff nests within their territories. 

This behavior demonstrates the 

flexibility in nest site selection that bald 

eagles have throughout the entire 

geographic range of the eagle, suggesting 

that nest site selection in the Sonoran 

Desert area is not likely ecologically or 

biologically important to the taxon as a 

whole. 

We also considered whether the 

juvenile migration characteristics of 

Arizona bald eagles may suggest 

adaptation to the Sonoran Desert Area 

that is biologically or ecologically 

important to the taxon as a whole. 

Juvenile bald eagles from Arizona 

migrate north in the spring and return 

to natal territories in the fall (Hunt et al. 

1992, p. A–v). 

Hunt et al. (2009, p. 125) indicates 

that juvenile bald eagles from Arizona 

exhibit similar migrating characteristics 

to each other, and that the similarity of 

these characteristics, which were 

exhibited while migrating solitarily, is 

evidence of genetic control of migration. 

In other words, juvenile bald eagles 

behave similarly even while migrating 

individually. Kerlinger (1989, p. 57) 

discusses that natural selection has 

likely shaped the migratory strategy of 

birds. Natural selection likely exerts 

pressure over time to emphasize the 

survival of successful migration 

strategies and, therefore, successful 

genes. In other words, birds that make 

errors in migration are eliminated from 

the population, and do not go on to 

reproduce and pass their genes to the 

next generation. Thus, the birds that do 

survive migration and reproduce 

successfully may become more 

genetically similar. Accordingly, there is 

a belief that the migration 

characteristics of bald eagles in the 

Sonoran Desert Area demonstrates 

adaptation in this population with 

respect to juvenile migratory behaviors. 

Bald eagles as a species exhibit a 

‘‘complex pattern of migration 

dependent on age of the individual 

(immature or adult), location of 

breeding site (north vs. south, interior 

vs. coastal), severity of climate at 

breeding site (especially during winter 

but also possibly during summer), and 

year-round food availability’’ (Buehler 

2000). For example, bald eagles in 

northeastern North America migrate 

south in the fall and return north in the 

spring, whereas bald eagles in Florida 

move north in late spring and early 

summer and return south in the fall 

(Kerlinger 1989, p. 12). This wide 

variety of migration strategies employed 

throughout the range of the species 

further demonstrates the flexibility of 

the species and further suggests that 

migrating characteristics of bald eagles 

in the Sonoran Desert area are not likely 

ecologically or biologically important to 

the taxon as a whole. 

Finally, we consider whether there 

may be other considerations that make 

persistence in the Sonoran Desert 

significant to the bald eagle as a whole. 

We conclude that, if other populations 

of the bald eagle could not persist in the 

Sonoran Desert ecological setting, that 

might be an indication that the 

population has adapted in a way that 

could be significant to the bald eagle as 

a whole. We currently have no direct 

evidence proving or disproving the 

ability of other bald eagles to persist in 

the Sonoran Desert area. As mentioned 

above, the best available information 

suggests that in fact there has been very 

little immigration into the Sonoran 

Desert area. Nevertheless, an adult bald 

eagle located at a Sonora, Mexico 

breeding area in 1992 possibly 

originated from Texas or Florida. This 

could indicate that, in the rare instances 

in which eagle immigrate to the Sonoran 

Desert Area from other areas, they are 

able to persist there. Moreover, based on 

the general adaptability shown by eagles 

throughout their range, there is no 

reason to suspect that eagles from 

outside the Sonoran Desert Area would 

not be successful in the Sonoran Desert 

Area over time. 

In summary, the combination of a 

highly adaptable species persisting in a 

varied habitat base leads us to conclude 

that the particular variations displayed 

in the Sonoran Desert Area population 

do not make that population more 

ecologically or biologically important 

than any other individual population. 

Therefore, while the Sonoran Desert 

Area represents a unique set of habitat 

characteristics, persistence of that 

population of bald eagles among those 

habitat characteristics is not significant 

(i.e., biologically or ecologically 

important) to the taxon as a whole. This 

is consistent with the Service’s prior 

interpretations of the DPS Policy, and, 

as such, the Service has not adopted a 

new interpretation of the DPS Policy. 

Significant Gap in the Range of the 

Taxon 

The second consideration under the 

DPS Policy in determining whether a 

population is significant to the taxon to 

which it belongs is ‘‘evidence that loss 

of the discrete population segment 

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would result in a significant gap in the 

range of a taxon’’ (61 FR 4725). We 

therefore evaluated whether a 

hypothetical extirpation of the Sonoran 

Desert Area bald eagle would leave a 

significant gap in the range because of: 

(1) The size of the Sonoran Desert Area 

population in relation to the size of the 

taxon as a whole; (2) an unlikelihood 

that other populations would immigrate 

and repopulate that part of the range; (3) 

distinctive traits or genetic variation 

among the Sonoran Desert Area bald 

eagle; (4) the size of the range of the 

Sonoran Desert Area population in 

relation to the size of the range of the 

taxon as a whole; or (5) the role that the 

geographical location where the 

Sonoran Desert Area population occurs 

plays with respect to the status of the 

bald eagle as a whole. 

Bald eagles in the Sonoran Desert 

Area are neither numerous nor 

constitute a significant percentage of the 

total number of bald eagles throughout 

the range of the taxon. In 2009, 48 pairs 

were documented in the Arizona 

portion of the Sonoran Desert Area 

(ADFG 2009a, p. 8), which is where 

most of the birds in the Sonoran Desert 

Area population occur. This represents 

less than one half of 1 percent of the 

current estimated number of breeding 

pairs of bald eagles in the lower 48 

States. Because the taxon as a whole 

also includes bald eagles in Canada and 

Alaska, the number of breeding pairs in 

the Sonoran Desert Area represents 

much less than one half of a percent of 

the number of breeding pairs throughout 

the range of the species. In addition, the 

Arizona portion of the Sonoran Desert 

Area did not support a large proportion 

of the bald eagle population historically. 

A small number, estimated at 15–20 

breeding pairs, historically bred in this 

area (Tilt 1976, p. 15). Given the 

historical and current population 

number of bald eagles throughout the 

range of the taxon, the Sonoran Desert 

Area population of bald eagles 

represents a relatively small number of 

breeding pairs in comparison. 

Loss of the Sonoran Desert Area bald 

eagles would be likely to create some 

gap in the range of the taxon. As 

discussed in the Discreteness section 

above, available evidence indicates that 

little immigration into this population 

has occurred. The small number of bald 

eagles and large distances between 

neighboring populations currently limit 

immigration and emigration between 

them, and bald eagles in the neighboring 

populations would have to increase 

their population size and expand their 

distribution to occupy the gaps, such 

that loss of the Sonoran Desert Area 

population would be likely to create a 

gap. Therefore, it is unknown whether 

bald eagles would naturally repopulate 

the Sonoran Desert Area if extirpated. 

However, it is not clear that any gap 

created in the range would be 

significant to the taxon as a whole. As 

discussed above, bald eagles in the 

Sonoran Desert Area are neither 

numerous nor constitute a significant 

percentage of the total number of bald 

eagles throughout the range of the taxon. 

Moreover, as discussed previously, 

there has been no evidence of 

distinctive traits or genetic variations 

among the Sonoran Desert Area 

population that suggests that loss of the 

population would have a negative effect 

on the bald eagle as a whole. For 

instance, we found no indication that 

bald eagles in the Sonoran Desert Area 

have a specialized prey base of native 

desert fishes, nor did we find any direct 

evidence for adaptation based on 

difference egg shell porosity or body 

size. 

Further, the actual amount of suitable 

bald eagle habitat in the Sonoran Desert 

Area is in general limited and represents 

a minute fraction of the total suitable 

habitat available for bald eagles 

throughout their range. The limited size 

of the current and historical bald eagle 

population in the Sonoran Desert Area 

directly reflects that fact. 

Finally, the Sonoran Desert Area itself 

does not play any particular role in the 

life history of the bald eagle such that 

loss of that part of the range would have 

a significant effect on the status of the 

species. For example, the Sonoran 

Desert Area is not the sole breeding or 

rearing location for bald eagles, nor is 

the Sonoran Desert Area only one of two 

parts of the species range such that loss 

of eagles in one part would result in a 

significant gap. As stated above, bald 

eagles are highly adaptable and are 

found across a wide range of habitats in 

North America. 

Having reviewed the best available 

scientific information with respect to 

the biological or ecological significance 

of the Sonoran Desert Area bald eagles, 

we have determined that loss of eagles 

in the Sonoran Desert Area would not 

represent a significant gap in the range 

of the bald eagle as a whole. 

In conclusion, while the loss of the 

Sonoran Desert Area bald eagle would 

likely result in some gap in the range of 

the taxon, we find that the gap does not 

constitute a significant gap in the range, 

such that information reviewed under 

this element does not suggest that 

Sonoran Desert Area bald eagles are 

biologically or ecologically significant to 

the taxon as a whole. 

Natural Occurrence of a Taxon 

Abundant Elsewhere as an Introduced 

Population 

The third consideration under the 

DPS Policy is ‘‘evidence that the 

discrete population segment represents 

the only surviving natural occurrence of 

a taxon that may be more abundant 

elsewhere as an introduced population 

outside its historic range’’ (61 FR 4725). 

As discussed above, naturally occurring 

bald eagles occur throughout much of 

their historical range in North America; 

thus, the Sonoran Desert Area 

population does not represent the only 

surviving natural occurrence of the bald 

eagle throughout the range of the taxon 

in North America. 

Genetic Characteristics 

As stated in the DPS Policy, in 

assessing the significance of a discrete 

population, the Service considers 

evidence that the discrete population 

segment differs markedly from other 

populations of the species in its genetic 

characteristics (61 FR 4725). 

Limited studies have been completed 

assessing the genetic characteristics of 

Sonoran Desert Area bald eagles in 

comparison to bald eagles throughout 

the rest of the range. Hunt et al. (1992, 

pp. E–96 to E–110) contains two studies 

that represent the genetic work 

completed on the Arizona bald eagle 

population, which includes the majority 

of bald eagles in the Sonoran Desert 

Area. Vyse (reported in Hunt et al. 1992, 

pp. E–96 to E–104) completed a DNA 

fingerprinting analysis of eagles from 

California, Arizona, and Florida, and 

was unable to identify populationspecific genetic markers; however, the 

author notes that the results obtained 

could easily be explained by sampling 

procedures. Zegers et al. (reported in 

Hunt et al. 1992, pp. E–105 to E–110) 

conducted an enzyme electrophoresis 

analysis, and concluded that, although 

‘‘the bald eagle population in Arizona 

may have some genetic uniqueness, it is 

not significantly different from any 

other population. * * *’’ The authors 

go on to question the reliability of the 

results because of the low numbers of 

individuals sampled from most States 

and because of the few loci examined. 

In summary, Hunt et al. (1992, p. A– 

163) note that neither study detected 

alleles or gene fragments that were not 

detected in other populations. In 

conclusion, neither study resolved any 

specific genetic markers with which 

Arizona bald eagles could be 

differentiated from other populations. 

Therefore, given the assumptions and 

cautions in using the data, we have 

determined that the best available data 

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do not support a conclusion that bald 

eagles in the Sonoran Desert Area have 

genetic characteristics that are markedly 

different from other bald eagles. 

DPS Conclusion 

On the basis of the best available 

information, we conclude that the 

Sonoran Desert Area population of the 

bald eagle is discrete, but it is not 

significant (i.e., biologically or 

ecologically important) to the taxon as 

a whole. We have reviewed the best 

available scientific information, and the 

evidence relative to natal site fidelity in 

breeding birds, the limited number of 

eagles in neighboring States, and the 

results of 30 years of monitoring data 

indicating that few, if any, eagles 

immigrate to or emigrate from the 

Sonoran Desert Area bald eagle 

population. We conclude that the best 

available scientific information with 

respect to the discreteness requirements 

of the DPS Policy warrant considering 

the Sonoran Desert Area bald eagle 

population as discrete from other bald 

eagle populations in North America. 

We considered the four classes of 

information listed in the DPS Policy as 

possible considerations in making a 

determination as to significance, as well 

as all other information that might be 

relevant to making this determination 

for the Sonoran Desert Area population. 

The adaptability of the bald eagle allows 

its distribution to be widespread 

throughout the North American 

continent in a variety of habitat types. 

Further, the Sonoran Desert Area bald 

eagles do not appear to exhibit any 

direct or indirect adaptation or 

behavioral advantage that would 

indicate its persistence in the Sonoran 

Desert Area is biologically or 

ecologically important to the taxon as a 

whole. Moreover, we considered the 

other three considerations that the DPS 

Policy sets out for evaluating 

significance, and none of them provides 

evidence that the population is 

significant to the bald eagle as a whole: 

Loss of the population would not result 

in a significant gap in the range; the 

population does not represent the only 

surviving natural occurrence of the bald 

eagle; and the population’s genetic 

characteristics do not differ markedly 

from those of other bald eagle 

populations. 

We conclude that the discrete 

Sonoran Desert Area population of bald 

eagle does not meet the significance 

criterion of the DPS Policy, as detailed 

above and, therefore, is not a DPS 

pursuant to our DPS Policy. As a result, 

the Sonoran Desert Area population of 

bald eagles is not a listable entity under 

section 3(16) of the Act. 

The DPS Policy sets forth a three-step 

process for determining whether a 

vertebrate population as a separate 

entity warrants listing: (1) Determine 

whether the population is discrete; (2) if 

the population is discrete, determine 

whether the population is significant to 

the taxon as a whole; and (3) if the 

population is both discrete and 

significant, then evaluate the 

conservation status of the population to 

determine whether it is endangered or 

threatened (typically presented as a 5- 

factor analysis of the threats to the 

discrete population (threats assessment) 

followed by a determination of whether 

the population meets the definition of 

‘‘endangered species’’ or ‘‘threatened 

species’’). Although we have 

determined that the Sonoran Desert 

Area population of the bald eagle does 

not qualify as a DPS and, therefore, is 

not a listable entity because it is not 

significant to the taxon as a whole. 

However, we provide below a threats 

assessment of the Sonoran Desert Area 

population of the bald eagle and a 

determination of its conservation status. 

The DPS Policy neither requires nor 

prohibits completion of a threats 

assessment once we have determined 

that a population does not qualify as a 

DPS. Nevertheless, in this instance, we 

concluded that completing a threats 

assessment—and detailing the nature, 

scope, and likely effect of the threats to 

the population and the species—would 

provide us and the public with valuable 

information for understanding the status 

of the population. 

Summary of Information Pertaining to 

the Five Factors 

As discussed above, the bald eagle is 

known to have bred in every State and 

province in the United States and 

Canada except Hawaii (Johnsgard 1990, 

p. 145; Hunt et al. 1992, p. A9). Gerrard 

and Bartolotti (1988, p. 2) noted that, at 

the time Europeans first arrived on 

North America, bald eagles were 

believed to have nested on both coasts, 

along all major rivers and large lakes in 

the interior from Florida to Baja 

California in the south, and north to 

Labrador and Alaska. In general, three 

factors seem to determine the 

distribution and abundance of bald 

eagles and other raptors (i.e., birds of 

prey): (1) An adequate and accessible 

supply of food, (2) availability of nest 

sites, and (3) suitable foraging habitat 

(Johnsgard 1990, pp. 15–17). 

Specifically, the bald eagle needs areas 

for nesting, perching, roosting, and 

foraging (Stalmaster 1987, pp. 119–131) 

and a reasonable degree of freedom from 

disturbance during the nesting season 

(Johnsgard 1990, p. 145). Hunt et al. 

(1992, p. A–v) goes further to suggest 

that the features of bald eagle habitat in 

Arizona that render it suitable for 

breeding include: (1) Nesting substrate 

offering security from large predators 

and human disturbance; and (2) two or 

more of the following fish taxa 

occurring in substantial numbers: carp, 

suckers (spp.), catfish (spp.), and 

perciforms (from the order Perciformes). 

Factors that appear to increase habitat 

quality include: (1) Reservoirs 

supporting warm water fisheries; (2) 

reservoir inflow areas; and (3) areas of 

river habitat containing fast, shallow 

water, moderate slope, turbulence, and 

exposed substrate that are maintained 

under a wide variety of flows. 

Observations of bald eagles in Arizona 

are mentioned in the literature as early 

as 1866 by Coues in the vicinity of Fort 

Whipple (now Prescott). Henshaw 

reported bald eagles south of Fort 

Apache in 1875. The first bald eagle 

breeding information was recorded in 

1890 near Stoneman Lake by S.A. 

Mearns. Additionally, Bent reported the 

presence of breeding eagles on the Salt 

River Bird Reservation, which was 

inundated by Roosevelt Lake in 1911. 

There are also reports from the 1930’s of 

bald eagles nesting along rivers in the 

White Mountains and along the Salt and 

Verde Rivers in central Arizona (Hunt et 

al. 1992, pp. A11–A12). 

The bald eagle population of the 

Southwest Recovery Region, as 

identified in the Service’s final recovery 

plan for the species, reaches all of New 

Mexico and Arizona, throughout 

Oklahoma and Texas west of the 100th 

meridian, and the area of California 

bordering the Lower Colorado River 

(Service 1982, p. 1). The vast majority 

of the breeding bald eagles from this 

population are found within the State of 

Arizona, most of which are located 

within the Sonoran Desert Area. The 

occurrence of breeding bald eagles in 

the State of New Mexico is very limited 

(USFS 2004, p. 153). In 2001, the New 

Mexico Department of Game and Fish 

(NMDGF) reported the occurrence of 

four bald eagle nest sites, all on private 

lands, in New Mexico. 

Nationwide, bald eagles are known to 

nest primarily along seacoasts and 

lakeshores, as well as along banks of 

rivers and streams (Stalmaster 1987, p. 

120). In Arizona, bald eagle breeding 

areas (eagle nesting sites and the area 

where eagles forage) are located in close 

proximity to a variety of aquatic sites, 

including reservoirs, regulated river 

systems, and free-flowing rivers and 

creeks. In Arizona, nests are placed 

mostly on cottonwood trees, cliff edges, 

and rock pinnacles and may be used 

year after year. However, living and 

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dead junipers, pinyon pines, sycamores, 

willows, and ponderosa pines, and 

artificial structures also have supported 

eagle nests (Driscoll et al. 2006, p. 4). In 

1992, of 111 known nests in Arizona 

within 28 breeding areas, 48 percent 

were on cliffs or pinnacles, 51 percent 

were on trees or snags, and one percent 

was on artificial structures. For breeding 

areas where both cliff and tree nests 

were available, cliff nests were selected 

73 percent of the time, while tree nests 

were selected 27 percent of the time 

(Hunt et al. 1992, p. A17). Additionally, 

eagles nesting on cliffs were found to be 

slightly more successful in raising 

young to fledgling, though the 

difference was not statistically 

significant (Hunt et al. 1992, p. A17). 

In the Sonoran Desert Area, essential 

bald eagle activities such as nesting, 

perching, roosting, and foraging occur 

from and in the large woody tree 

component of the riparian habitat found 

along rivers and streams. Eagles nesting 

in trees within the Sonoran Desert Area 

are less susceptible to heat stress and 

parasites than those nesting in cliff or 

pinnacle nests, but are more vulnerable 

to disturbance from the ground and 

from inundation during flooding (Hunt 

et al.1992, p. A17). Eaglets (young 

eagles) in tree nests are less likely to die 

from premature fledging. An abundance 

of trees provides more perching 

locations to capture prey, more 

locations to place nests, and greater 

opportunities to partition resources in 

order to increase territory density (Hunt 

et al.1992, pp. Aii, A21, A135). 

The importance of riparian trees is 

demonstrated along the lower Verde 

River in Arizona, where the densest 

population of nesting bald eagles (seven 

territories along 30 river kilometers 

(18.6 miles)) exclusively uses 

cottonwood trees for nest placement. In 

Arizona, the majority of nests are 

located in the Upper and Lower 

Sonoran Life Zones (zones of plant and 

animal life associated with a given 

elevation), including the riparian 

habitats and transition areas of both 

zones (Hunt et al. 1992, p. A17). 

Representative vegetation of these life 

zones includes Arizona sycamore 

(Platanus wrightii), blue palo verde 

(Parkinsonia florida), cholla (Opuntia 

and Cylindropuntia spp.), Fremont 

cottonwood (Populus fremontii), 

Gooding willow (Salix gooddingii), 

mesquite (Prosopis spp.), saguaro 

(Carnegiea gigantea), and tamarisk or 

salt cedar (Tamarix pentandra; an 

exotic species) (Brown 1994, p. 200). 

Bald eagles primarily eat fish, but 

they will also eat amphibians, reptiles, 

birds, small mammals, carrion (dead 

animals), and carcasses of large 

mammals (cows, elk, deer, etc.). Their 

food habits can change daily or 

seasonally, but when a choice is 

available, bald eagles invariably select 

fish over other prey. Bald eagles will 

scavenge, steal, or actively hunt to 

acquire food. Carrion constitutes a 

higher proportion of the diet for 

juveniles and subadults than it does for 

adult eagles. Bald eagles are primarily 

sit-and-wait hunters, perching in trees 

in order to detect available prey 

(Stalmaster 1987, p. 104). Food strongly 

influences bald eagle productivity 

(young fledged per occupied territory) 

(Newton 1979, pp. 95–96, 101–106; 

Hansen 1987, p. 1389). A female’s 

health in the months preceding egglaying can affect egg production, and 

prey availability during the breeding 

cycle affects the survivorship of 

nestlings and post-fledging juveniles. 

Any factor affecting the adults’ ability to 

acquire food can influence productivity 

and adult survival (Newton 1979, pp. 

95–96, 101–106). 

The most common fishes eaten in 

Arizona are Sonora (Catostomus clarki) 

and desert suckers (Catostomus 

insignis); channel (Ictalurus punctatus) 

and flathead catfish (Pylodictis olivaris); 

common carp (Cyprinus carpio); 

largemouth (Micropterus salmoides), 

smallmouth (Micropterus dolomieui), 

yellow (Morone mississippiensis), and 

white bass (Morone chrysops); and black 

crappie (Pomoxis nigromaculatus). Less 

common are roundtail chub (Gila 

robusta), green sunfish (Lepomis 

cyanellus), bluegill (Lepomis 

macrochirus), tilapia, and rainbow trout 

(Oncorhynchus mykiss) (Service 1982, 

p. 11; Driscoll et al. 2006, p. 6). The 

introduction of predatory flathead 

catfish in the late 1970s nearly 

extirpated native fish populations on 

the upper Salt River (Driscoll et al. 

2006, p. 19). Flathead catfish, while 

available as bald eagle prey when 

smaller, grow to large sizes (up to 50 

pounds, or 22.6 kilograms) making them 

unavailable as a prey item (i.e., too large 

for bald eagles to take). Flathead catfish 

populations have increased while other 

fish species have decreased (Driscoll et 

al. 2006, p. 19). 

The Arizona Game and Fish 

Department (AGFD) notes that apparent 

changes in eagle productivity observed 

from before 1985 and after 1985 could 

be the result of a difference in 

monitoring protocols. Starting in 1985, 

their protocol incorporated monthly 

helicopter surveys of all breeding areas. 

The AGFD noted that the average 

productivity rate of 0.78 observed in 

Arizona between 1987 and 2005 is 

consistent with that observed in other 

areas of the species’ range with larger 

populations, including Minnesota, 

British Columbia, Interior Alaska, and 

Washington (Driscoll et al. 2006, p. 5). 

Due to rugged terrain, the earliest formal 

surveys in Arizona—in the 1970’s—only 

detected bald eagle breeding areas that 

were easily accessible (e.g., along rivers 

and streams) (Driscoll et al. 2006, p. 9). 

Following intensive survey efforts over 

the last 25 years, the AGFD is aware of 

more breeding areas, and habitat 

conditions within them varies greatly. 

As a result, the AGFD is currently 

tracking productivity in breeding areas 

with a variety of habitat conditions, 

rather than tracking productivity in only 

those breeding areas that were easily 

detected. While the number of breeding 

areas detected in subsequent surveys in 

Arizona has increased, there is no 

expectation that pairs using these 

breeding areas would demonstrate 

increased reproductive performance. 

Productivity data between 1987 and 

2008 indicates less variability. For 

example, in 1971, with only three 

known breeding areas, productivity was 

1.33; in 1972 productivity was 0.0; and 

in 1973 productivity was 1.4. By 

comparison, with more breeding areas 

known, productivity now varies by only 

0.20 to 0.30 units (Driscoll et al. 2006, 

pp. 48–50; AGFD 2007, pp. 33–34; 

AGFDa 2008, pp. 38–39). 

The Sonoran Desert Area population 

consists of those bald eagles that breed 

predominantly within central and 

southern Arizona; Sonora, Mexico 

(Sonora); and portions of southeastern 

California along the Colorado River as 

described in detail above (see Distinct 

Population Segment). Based on 

opportunistic monitoring of the single 

nest located in southern California at 

the Copper Basin breeding area 

conducted since 2001 (Melanson 2006a, 

2007, 2008, pers. comm.), we have 

limited information on potential threats 

to this breeding area, and demographic 

data from this site was not collected 

using the same protocol established in 

Arizona. We include information from 

this breeding area in the following 

threats analysis where appropriate. 

Information on breeding success in 

Sonora is limited. Bald eagle territories 

were first recorded in Sonora along the 

Rio Yaqui drainage in 1986 (Brown et al. 

1986, pp. 7–14). Since that time, a total 

of eight bald eagle breeding areas have 

been verified (Driscoll and Mesta 2005, 

in prep.). Surveys there irregularly 

occur due to difficulties in accessing 

breeding areas. However, given the 

limited number of breeding areas and 

the infrequency of breeding noted 

during survey years, the overall impact 

of productivity from Sonora bald eagles 

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to the total productivity of the Sonoran 

Desert Area population of the bald eagle 

is minimal. 

Historical records, literature, past 

reports, and interviews with agency 

personnel and other people 

knowledgeable about bald eagles in 

Arizona indicated that there was one 

known breeding area by the 1920s, two 

by the 1930s, four by the 1940s, five by 

the 1950s, six by the 1960s, and eight by 

the 1970s (Hunt et al. 1992, pp. C56– 

C61). The number of known breeding 

areas within the Sonoran Desert Area 

increased from a low of three in 1971 to 

a high of 52 in 2009. In addition, there 

were seven breeding areas located 

within Arizona but outside of the 

Sonoran Desert Area in 2009. From 1985 

to 2009, productivity within the 

Sonoran Desert Area has ranged from a 

low of 0.54 in 1990 and 1992 to a high 

of 1.17 in 2008. The mean annual 

productivity for this time period in the 

Sonoran Desert Area was 0.81 (AGFD 

2004, pp. 30–31; AGFD 2005, pp. 34–35; 

AGFD 2006a, pp. 35–36; AGFD 2007, 

pp. 33–34; AGFD 2008a, pp. 38–39; 

Allison et al. 2008, pp. 17–18; AGFD 

2009a, pp. 42–43). For comparison, 

productivity in North America averaged 

0.34 in three declining bald eagle 

populations, as compared to 0.75 in 

seven stable populations and 1.03 in 

four increasing populations (Swenson et 

al. 1986, p. 25). 

Productivity data alone does not 

provide a clear indication of the status 

of a population without considering the 

additional influence of other 

demographic variables (e.g., survival, 

number of breeding areas). When all of 

this data is considered together, as is 

done through a population viability 

analysis (see Factor A discussion), 

estimates of population growth and 

extinction probabilities can be 

generated. For bald eagles nesting in the 

Sonoran Desert Area of Arizona, a 

population viability analysis conducted 

by the Service resulted in an estimated 

annual population growth rate of two 

percent, and none of the model 

iterations resulted in extinction of the 

population (Millsap 2009, in prep.) (see 

Factor E, Demographic Factors 

discussion). 

Five-Factor Analysis 

Pursuant to section 4 of the 

Endangered Species Act of 1973, as 

amended, we must determine whether 

any species, subspecies, or DPS of 

vertebrate taxa is an endangered or 

threatened species because of any of the 

following five factors: (A) Present or 

threatened destruction, modification, or 

curtailment of habitat or range; (B) 

overutilization for commercial, 

recreational, scientific, or educational 

purposes; (C) disease or predation; (D) 

inadequacy of existing regulatory 

mechanisms; or (E) other natural or 

manmade factors affecting its continued 

existence. The Endangered Species Act 

identifies the five factors to be 

considered, either singly or in 

combination, to determine whether a 

species may be threatened or 

endangered. Our evaluation of these 

threats in terms of the petitioned action 

to list the Sonoran Desert Area 

population of the bald eagle as a distinct 

population segment (DPS) is presented 

below. Throughout this finding we refer 

to the Sonoran Desert Area population 

of the bald eagle, because that is the 

petitioned entity; however, we have 

determined that this population does 

not constitute a DPS and, therefore, is 

not a listable entity. Even though we 

have made this determination, we 

conducted the five-factor analysis below 

as an exercise to review the status of the 

Sonoran Desert Area population of the 

bald eagle. 

In considering what factors might 

constitute a threat, we must look beyond 

the mere exposure of the species to the 

factor to determine whether the species 

responds to the factor in a way that 

causes actual impacts to the species. If 

there is exposure to a factor, but no 

response, or only a positive response, 

that factor is not a threat. If there is 

exposure and the species responds 

negatively, the factor may be a threat 

and we then attempt to determine how 

significant a threat it is. If the threat is 

significant, it may drive or contribute to 

the risk of extinction of the species such 

that the species warrants listing as 

threatened or endangered as those terms 

are defined by the Endangered Species 

Act. This does not necessarily require 

empirical proof of a threat. The 

combination of exposure and some 

corroborating evidence of how the 

species is likely to be negatively affected 

could suffice. The mere identification of 

factors that could affect a species 

negatively is not sufficient to compel a 

finding that listing is appropriate; we 

require evidence that these factors are 

operative threats that act on the species 

to the point that the species meets the 

definition of ‘‘threatened species’’ or 

‘‘endangered species’’ under the 

Endangered Species Act. 

The following analysis considers all 

known threats to bald eagles in the 

Sonoran Desert Area, as described 

below. Factors that are believed to have 

affected or continue to affect bald eagles 

in the Sonoran Desert Area include the 

degradation or loss of riparian habitat; 

loss of surface flows from groundwater 

pumping and surface water diversions; 

demographic factors; declining prey 

base; contaminants, pollutants, and 

eggshell thinning; climate change; and 

human disturbance. It is important to 

recognize that in most areas where bald 

eagles occur, two or more factors may be 

acting in combination in their influence 

on individuals of the population, the 

entire local population, or the suitability 

of habitat. 

Within the Sonoran Desert Area, bald 

eagles on the Verde River accounted for 

44 percent of total productivity between 

1971 and 2008 while breeding areas on 

the Salt River accounted for an 

additional 34 percent of total 

productivity. In total, 78 percent of bald 

eagle productivity in the Sonoran Desert 

Area, exclusive of Sonora, is tied to 

breeding areas along these two river 

systems. Therefore, the following 

analysis places emphasis on threats to 

breeding areas along these two river 

systems. We also included threats to 

other river systems—including the Agua 

Fria, Bill Williams, and Gila Rivers—in 

our analysis of threats to bald eagles in 

the Sonoran Desert Area. 

In our analysis of Factors A through 

E below, we describe current threats, as 

well as threats that we anticipate will 

increase, or will be realized in the 

future. For populations within Arizona, 

our analysis benefitted from the 

availability of specific research, 

monitoring, and other studies. The 

analysis of these factors as they pertain 

to the status and threats to the bald 

eagle in mainland Sonora is broader in 

scope, focusing on regional or statewide 

areas, because there has been less work 

completed for the bald eagle in this area. 

In some instances, we include a 

discussion on more refined geographic 

areas of Mexico when supported by the 

literature. 

Traditional Ecological Knowledge 

We included traditional ecological 

knowledge from Native American tribes 

in our consideration of threats to the 

Sonoran Desert Area population of bald 

eagle. Traditional ecological knowledge 

includes an intimate and detailed 

knowledge of plants, animals, and 

natural phenomena; the development 

and use of appropriate technologies for 

hunting, fishing, trapping, agriculture, 

and forestry; and a holistic knowledge, 

or ‘‘world view,’’ that parallels the 

scientific discipline of ecology (Bourque 

et al. 1993, p. vi). Native people 

depended upon the animals and plants 

of these environments for food, clothing, 

shelter, and companionship and as a 

result developed strong ties to the fish 

and land animals, the forests, and the 

grasslands (Pierotti and Wildcat 1999, 

pp. 192–195). We include bald eagle 

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traditional ecological knowledge 

provided to us by the White Mountain 

Apache Tribe, San Carlos Apache Tribe, 

Tonto Apache Tribe, Yavapai-Apache 

Nation, Salt River-Pima Maricopa 

Indian Community, Tohono O’odham 

Nations, and Fort McDowell Yavapai 

Nation. 

Traditional ecological knowledge 

from the White Mountain Apache Tribe, 

San Carlos Apache Tribe, Tonto Apache 

Tribe, and Yavapai-Apache Nation 

(collectively referred to as Western 

Apache) indicates that bald eagles are 

absent from many nest sites where they 

were once observed. Feathers 

originating from native, living, wild 

bald eagles are obtained year round for 

ceremonial purposes. Part of the ritual 

use of these feathers requires obtaining 

power from the place in which the eagle 

lives, and, thus, these places are 

considered extremely powerful and are 

known to the user. The task of obtaining 

feathers is only accomplished by certain 

individuals who have cultural 

knowledge and the traditional 

ecological knowledge of these places. 

This knowledge is gained from years of 

experience through observation, which 

is then orally transferred to the next 

generation. Western Apache traditional 

ecological knowledge suggests that 

irresponsible urban expansion, 

agriculture, mining, and resultant 

climate change have brought the earth, 

and bald eagle habitat, to a crisis point. 

Traditional ecological knowledge 

additionally suggests that the riparian 

systems on which bald eagles depend 

have been severely damaged, and 

continue to be threatened with upland 

watershed decline, the region’s 

dwindling water resources, multiple 

sources of pollution, water rights 

conflicts, and the spread of nonnative 

fauna species (Lupe et al. 2008, pers. 

comm.). Tribal information is consistent 

with published information 

documenting the modification and 

destruction of aquatic and riparian 

communities in the southwestern 

United States (Medina 1990, p. 351; 

Sullivan and Richardson 1993, pp. 35– 

42; Fleischner 1994, pp. 630–631; 

Stromberg et al. 1996, pp. 113, 123–128; 

Belsky et al. 1999, pp. 8–12; Webb and 

Leake 2005, pp. 305–310). 

Traditional ecological knowledge 

from the Western Apache reports a 

decline of the bald eagle population and 

nesting sites throughout Arizona over 

the past 150 years. Bald eagle nests are 

no longer present in sites where they 

were known to the Western Apache, 

including Warm Springs Canyon, Black 

River Canyon, Paymaster Canyon, and 

Salt Creek Canyon on the San Carlos 

Reservation. According to traditional 

ecological knowledge of the Western 

Apache, more bald eagles were 

previously observed below Coolidge 

Dam and at Talkalai Lake than currently 

exist. In addition, bald eagles are no 

longer present in the canyon above 

Clarksdale, Box Canyon, Fossil Creek, 

Courthouse Butte around the Sedona 

area; Mazatzal Mountains near Payson; 

and Hackberry Mountain southeast of 

Camp Verde (Sparks 2009, entire). 

According to transcripts from a 

government-to-government consultation 

meeting held on July 3, 2008, the Fort 

McDowell Yavapai Nation reported up 

to 15 bald eagle nests historically 

occurred on their reservation lands, and 

now there are four. Western Apache 

experts with traditional ecological 

knowledge about the bald eagle note 

atmospheric changes, and alteration in 

bee, wasp, and hornet populations, as a 

few of the many key factors in bald 

eagle habitat decline. Declines and 

shifts in distribution and abundance in 

bald eagles in Arizona may have 

occurred within the last 150 years from 

areas where habitat and riverine systems 

may no longer exist (Mearns 1890, p. 53; 

Hunt et al. 1992, Ai, A10–A12; Mighetto 

et al. 2009, pp. 6–8). For example, 

Mighetto et al. (2009) reported eagles 

historically occupying areas around 

Window Rock, Lake Mead, Anderson 

Mesa near Big Horse Lake, Stoneman 

Lake, Fort Apache, and Mt. Graham, but 

they no longer exist in these locations. 

The Salt River Pima-Maricopa Indian 

Community believes the Bald and 

Golden Eagle Protection Act (see 

discussion under Factor D below) will 

not provide the necessary level of 

protection needed to keep the bald eagle 

in the Sonoran Desert Area viable. The 

Community further believes that habitat 

protection is uncertain based on the 

new regulatory definition of ‘‘disturb,’’ 

which is untested in the courts. The 

Western Apache have expressed similar 

concern that habitat will not be 

protected. The Western Apache Tribes 

and Nation have indicated that, within 

reservation boundaries, there may be 

inadequate resources to address these 

threats. They indicate that the incentive 

for poaching bald eagles is high in 

Apache communities, primarily due to 

desperate economic conditions. A single 

bald eagle can be sold for more than 

$5,000. The Western Apache believe 

that even a perceived loss of protection 

for the bald eagle could bring about an 

increase in poaching activities. Tribal 

law enforcement agencies, already 

facing funding shortages, would be 

unable to respond properly to such 

threats (Lupe et al. pers. comm. 2008). 

A. Present or Threatened Destruction, 

Modification, or Curtailment of the 

Species’ Habitat or Range 

Within Arizona, bald eagles are listed 

as a Tier 1a ‘‘species of greatest 

conservation need’’ in the State’s 

‘‘Comprehensive Wildlife Conservation 

Strategy’’ (AGFD 2006b, p. 155). 

Additional provisions are in place for 

the management of bald eagles. The 

management of bald eagles in Arizona is 

also overseen by the Southwestern Bald 

Eagle Management Committee, which is 

a multiparty committee initiated in 1984 

that focuses on coordination of bald 

eagle conservation efforts in Arizona 

across various land ownerships. The 

AGFD, in 2006, developed the 

‘‘Conservation Assessment and Strategy 

for the Bald Eagle in Arizona,’’ which 

described the current threats to bald 

eagles in Arizona and identified the best 

management practices necessary to 

maintain their distribution and 

abundance post-delisting. The 

‘‘Conservation Assessment and Strategy 

for the Bald Eagle in Arizona’’ has been 

implemented following the signing of a 

Memorandum of Understanding in 

2007. As a result, the AGFD continues 

to conduct bald eagle winter counts, 

monitor bald eagle distribution and 

productivity, support the ABENWP, and 

conduct other activities identified in the 

‘‘Conservation Assessment and Strategy 

for the Bald Eagle in Arizona.’’ The 

AGFD believes that these conservation 

efforts will sufficiently manage the 

threats to bald eagles in the Sonoran 

Desert Area of Arizona absent the 

protections under the Endangered 

Species Act (AGFD 2008b, p. 6). 

A number of potential threats to bald 

eagle habitat in the Sonoran Desert Area 

have been identified by the petitioners, 

the AGFD, and the Service. In our 

review of the best scientific and 

commercial data available, activities 

that are potentially affecting bald eagles 

and their habitat in the Sonoran Desert 

Area include urban and rural 

development, livestock grazing, 

groundwater pumping, and surface 

water diversions, in that each of these 

activities (or a combination of these 

activities, acting in concert) could 

degrade or remove riparian habitat. 

Because bald eagles rely on aquatic 

ecosystems as a source of fish for 

survival and reproduction and trees for 

nesting, any loss or degradation of 

riparian habitat is of particular concern 

(Stalmaster 1987, pp. 159, 170–171). 

The ‘‘Conservation Assessment and 

Strategy for the Bald Eagle in Arizona’’ 

identified riparian degeneration as a 

management challenge for 25 of 45 

known breeding areas (or 58 percent) 

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located within the Sonoran Desert Area 

of Arizona at that time (Driscoll et al. 

2006, pp. 51–53). Additionally, the 

potential loss of surface flows within 

sections of the Gila, Salt, Verde, Agua 

Fria, or Bill Williams Rivers would 

likely have negative impacts on the 

density and distribution of prey and the 

health and persistence of riparian 

vegetation. Below we present 

information about these factors, and 

discuss the magnitude and extent of the 

impacts from these factors on the 

Sonoran Desert Area population of the 

bald eagle. 

Degradation and Loss of Riparian 

Habitat 

Riparian communities are sensitive to 

even low levels (less than 10 percent) of 

urban development within a watershed 

(Wheeler et al. 2005, p. 154). 

Development along or in proximity to 

riparian zones can alter the nature of 

stream flow dramatically, changing 

once-perennial streams into ephemeral 

streams, which has direct consequences 

on the riparian community (Medina 

1990, pp. 358–359). The distribution of 

breeding bald eagles in the Sonoran 

Desert Area follows major watersheds, 

with the highest productivity occurring 

along the Salt and Verde Rivers, and 

some of the breeding areas along these 

rivers are located in close proximity to 

metropolitan areas. The conversion of 

perennial streams into ephemeral 

(lasting a short time) streams or loss of 

open space can directly affect bald 

eagles along these rivers (Medina 1990, 

pp. 358–359; Ewing et al. 2005, p. 11). 

Loss of water and conversion to 

ephemeral streams eliminates or 

reduces the quality of riparian habitat, 

including the trees on which bald eagles 

depend for nesting and perching. Loss 

of open space or clearing of habitat for 

development removes vegetation 

directly, either in the watershed or in 

the riparian areas themselves, making 

the areas less suitable for bald eagles by 

removing key habitat components (e.g., 

water, large trees). 

The influence of urbanization and 

development can be observed within the 

greater Phoenix, Arizona, area, where 

impacts have modified riparian 

vegetation, structurally altered stream 

channels, facilitated nonnative fish 

species introductions, and dewatered 

large reaches of formerly perennial 

rivers where the bald eagle historically 

occurred (portions of the Gila and Salt 

Rivers). Urbanization on smaller scales 

can also affect habitat suitability for the 

bald eagle. Regional development and 

subsequent land use changes spurred by 

increasing human populations along 

lower Tonto Creek and within the Verde 

Valley may negatively affect the 

suitability of this habitat for bald eagles 

by reducing the quantity and quality of 

aquatic resources for native fish and 

reducing the width of riparian habitat 

(Paradzick et al. 2006, pp. 89–90). 

Studies conducted in other portions of 

the range of the bald eagle in North 

America, such as the Chesapeake Bay, 

indicated that human development and 

low availability of suitable perch trees 

combined to affect bald eagle use of 

shoreline habitat (Chandler et al. 1995, 

pp. 328–330). Bald eagles there 

preferred shoreline segments that 

contained more suitable perch trees, 

more forest cover, and fewer buildings. 

However, to have a significant effect, 

urbanization and development must be 

occurring at a scale and intensity that 

results in a risk to the Sonoran Desert 

Area population of the bald eagle at the 

population level. The ‘‘Conservation 

Assessment and Strategy for the Bald 

Eagle in Arizona’’ identified 

development as a management concern 

in 4 of 45 bald eagle breeding areas (or 

9 percent) located within the Sonoran 

Desert Area of Arizona at that time 

(Driscoll et al. 2006, pp. 51–53). 

Although urbanization and 

development may be affecting breeding 

areas at a localized level, it does not 

appear that they are currently a threat at 

the population level, because the 

population remains stable or increasing. 

The effects of urban and rural 

development on riparian habitat are 

expected to increase as human 

populations increase. Arizona increased 

its population by 394 percent from 1960 

to 2000, and is second only to Nevada 

as the fastest growing State in terms of 

human population (Social Science Data 

Analysis Network (SSDAN) 2000, p. 1). 

Over the same time period, population 

growth rates increased in Arizona 

counties where the bald eagle occurs: 

Maricopa (463 percent), Yavapai (579 

percent), Gila (199 percent), Graham 

(238 percent), Apache (228 percent), 

and La Paz (142 percent) (SSDAN 2000). 

Population growth trends in Arizona are 

expected to continue into the future. 

The Phoenix metropolitan area, founded 

in part due to its location at the junction 

of the Salt and Gila Rivers, is currently 

a population center of 3.63 million 

people. Arizona is predicted to have the 

sixth largest net increase in population 

(slightly over two million people) in the 

nation between 1995 and 2025 (U.S. 

Department of Commerce 1997, p. 1). 

The human population in Maricopa 

County alone is expected to reach five 

million people by 2025 (City of Phoenix 

2004, p. 18), and the county stands to 

lose up to an estimated 347.2 square 

miles of open space that are currently in 

the path of development (Ewing et al. 

2005, p. 11). 

The human population in two towns 

along the Verde River, Cottonwood and 

Camp Verde, is expected to grow by 

approximately 70 and 77 percent, 

respectively, between 2006 and 2040 

(Arizona Department of Administration 

2012). The town of Chino Valley, at the 

headwaters of the Verde River, grew by 

22 percent between 2000 and 2004; Gila 

County, which includes portions of the 

Salt River and Tonto Creek, grew by 20 

percent between 2000 and 2003 (U.S. 

Census Bureau 2006). Human 

population growth is expected to 

continue to affect the riparian and 

aquatic communities of the Verde 

Valley through increased demand for 

water, increased runoff, shortened 

return intervals on flood events, water 

quality impacts, and increased 

recreational impacts where bald eagles 

are concentrated (Girmendock and 

Young 1997, p. 57; American Rivers 

2006, p. 30; Paradzick et al. 2006, p. 89). 

The human population and associated 

recreational developments in the 

Sonoran Desert Area, which are often 

tied to water bodies and riparian areas, 

are expected to continue to grow into 

the future. In the Sonoran Desert Area, 

an expanding human population has led 

to higher recreational use of riparian 

areas, as evidenced along reaches of the 

Salt and Verde Rivers in proximity to 

the Phoenix metropolitan area. 

Recreational impacts can include direct 

habitat losses for development of 

recreational facilities and infrastructure 

or indirect loss of habitat as a result of 

human disturbance (see Factor E for 

further discussion). Developments 

within occupied breeding areas include 

a turnaround for river tubing near 

Bulldog Cliffs (Salt River) and lakeside 

resorts on the north shore of Lake 

Pleasant. Additional developments that 

may affect bald eagle breeding areas 

include: a four-lane boat launch and a 

1,000 person per day recreation area on 

Bartlett Lake; a new day use and 

emergency boat launch constructed on 

the lower Salt River; a new RV park 

constructed within 1300 feet (396.2 

meters) of a nest on the lower Verde 

River; and a 100-unit campground and 

boat ramp along Tonto Creek (Driscoll et 

al. 2006, p. 14). 

In many of the breeding areas within 

the Sonoran Desert Area of Arizona, 

effects from development have been 

mitigated through the implementation 

of seasonal closures and monitoring by 

the Arizona Bald Eagle Nest Watch 

Program (ABENWP). The ABENWP, 

managed by the AGFD, closely monitors 

breeding bald eagles in areas with high 

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recreational pressure. This program was 

initiated in 1978 with the goals of 

public education, data collection, and 

conservation of the species. Nest 

watchers collect behavioral data, contact 

and educate the public in the vicinity of 

breeding areas, and identify potential 

threats to the breeding success of bald 

eagles. Funding for the ABENWP comes 

from a variety of sources, including 

State Wildlife Grants, donations, AGFD 

Heritage Funds (State lottery), matching 

funds for Federal grants, and 

contributions from Federal agencies. As 

a result of the bald eagle being delisted, 

there is the potential that the ABENWP 

could face funding shortages or that the 

bald eagle could receive less priority 

from partner agencies; however, there is 

currently no indication that either of 

these scenarios has occurred or will 

occur in the future. 

The AGFD’s Projects Evaluation 

Program is available for Federal 

agencies or companies with a Federal 

nexus. This program can be used to 

evaluate the impacts of planned or 

future projects in areas where there may 

be a species of concern. The AGFD 

believes the program will help to ensure 

bald eagles and their habitat are 

considered and evaluated for possible 

effects from development projects 

(Driscoll et al. 2006, p. 14). In the future, 

similar levels of development and 

modification as those described above 

can be expected as recreational facilities 

age and recreational pressures increase 

with increasing human populations. 

However, as evidenced by the continued 

reproductive success (e.g., pairs 

continue to produce young) of the above 

affected breeding areas, the ability of the 

bald eagle in the Sonoran Desert Area to 

adapt to increases in the human 

population and habitat modifications is 

an indication that these actions are not 

posing a significant risk at the 

population level. 

Livestock grazing has been a prevalent 

industry in the Southwest for 200 years 

or more. Poorly managed livestock 

grazing has damaged approximately 80 

percent of stream, cienega (spring), and 

riparian ecosystems in the western 

United States (Kauffman and Krueger 

1984, pp. 433–435; Weltz and Wood 

1986, pp. 367–368; Waters 1995, pp. 22– 

24; Pearce et al. 1998, p. 307; Belsky et 

al. 1999, p. 1). Overgrazing by domestic 

livestock has been a significant factor in 

the modification and loss of riparian 

habitats in the arid western United 

States (Schultz and Leininger 1990, p. 

295; Belsky et al. 1999, pp. 1–3). If not 

properly managed, livestock grazing can 

significantly alter watershed hydrology; 

water quality; aquatic and riparian 

ecology; and the structure and 

composition of riparian plant 

communities. Excessive grazing can also 

prevent the establishment of seedlings 

(Carothers 1977, p. 2; Glinski 1977, pp. 

119–121), which limits the growth of 

future nest and roost trees for bald 

eagles (Driscoll et al. 2006, p. 4). 

Important features of bald eagle 

habitat—such as large trees for roosting 

and nesting, sufficient flows, water 

temperatures, and water quality—are 

most affected by improper livestock 

grazing in riparian areas. Currently, 

active grazing is occurring within the 

Verde River floodplain in the Verde 

Valley, lower Verde River, and upper 

Salt River. 

The impacts of improper livestock 

grazing have been reduced on many 

streams, in part through consultations 

completed under section 7 of the 

Endangered Species Act and in part 

through improved grazing management 

practices. Some of the consultations 

were for other species that use the same 

streams as habitat or for foraging (e.g., 

Southwestern willow flycatcher 

(Empidonax trailii extimus), razorback 

sucker (Xyrauchen texanus), spikedace 

(Meda fulgida), loach minnow (Tiaroga 

cobitis)). Therefore, despite the delisting 

of the bald eagle, impacts from livestock 

grazing on streams will continue to be 

minimized through consultations 

conducted for those other species and 

their designated critical habitats. Along 

many portions of the Verde River and 

Tonto Creek, livestock grazing has 

currently been discontinued. Riparian 

recovery, at least in response to a 

reduction in grazing pressure, may 

therefore be underway in some of these 

areas. Improper livestock grazing may 

still be an added stressor on those 

systems where it continues to occur 

(absent a separately listed species), 

where trespass or unauthorized cattle 

are grazing, or where habitat is already 

degraded due to other factors. 

In Mexico, while the magnitude and 

significance of adverse effects to 

riparian communities related to 

development lags behind the United 

States due to slower population and 

economic growth, impacts to riparian 

and aquatic communities are currently 

occurring with increasing significance 

(Conant 1974, pp. 471, 487–489; 

Contreras Balderas and Lozano 1994, 

pp. 379–381; va Landa et al. 1997, p. 

316; Miller et al. 2005, pp. 60–61; 

Abarca 2006, pers. comm.; Rosen 2006, 

pers. comm.). Mexico’s population 

increased by 245 percent from 1950 to 

2002, and is projected to grow by 

another 28 percent by 2025 

(EarthTrends 2003, pp. 1–2). As a result 

of the North American Free Trade 

Agreement, the number of maquiladoras 

(export assembly plants) is expected to 

increase by as many as 3,000 to 4,000 

(Contreras Balderas and Lozano 1994, p. 

384). To accommodate Mexico’s 

increasing human population, rural 

areas are largely devoted to food 

production based on traditional 

methods, which has led to serious losses 

in vegetative cover and soil erosion (va 

Landa et al. 1997, p. 316). In addition, 

changes in land legislation within 

Mexico related to free market policies 

and local agricultural production 

methods may result in the loss of land 

management practices that protect the 

natural environment (Ortega-Huerta and 

Kral 2007, p. 1). Much of the riparian 

woodland in the broad floodplains 

along the Rio Bavispe has been cleared 

for agriculture and pasturelands. 

Similarly, portions of the riparian 

habitat along the Rio Yaqui have also 

been affected by agriculture, and heavy 

livestock grazing has occurred 

throughout the Rio Yaqui and Rio 

Bavispe (Brown et al. 1986, pp. 3, 5). In 

one breeding area along the Rio Yaqui, 

the nest failed in 1986 due to the 

construction of a fence in preparation 

for agricultural development. The nest 

was then destroyed in 1987 as a result 

of a fire set to clear the land for 

agriculture (Driscoll and Mesta 2005, in 

prep.). 

Several recent development projects 

in Mexico have affected bald eagle 

breeding areas. In 1998, a new road was 

created from the Town of Sahuaripa to 

the Rio Yaqui/Sahuaripa confluence, 

which was followed by a cement 

property marker placed above the 

eagle’s cliff nest in 1999 (Driscoll and 

Mesta 2005, p. 58). From 2000 to 2002, 

construction and completion of a new 

highway bridge occurred immediately at 

the Sahuaripa bald eagle nest, which 

had formerly been the most successful 

mainland Sonora bald eagle territory. 

Associated with the bridge construction, 

development of worker living quarters, 

an equipment staging area, and a 

construction material borrow site near 

the nest resulted in further habitat 

degradation. The placement and 

development of the new road and bridge 

generated increased human activity 

(e.g., fishing, swimming, picnics), and 

development of four ranch buildings in 

the Sahuaripa breeding area. In 2009, 

this pair was located in the vicinity of 

the Sahuaripa breeding area, and it is 

likely that they have relocated to a new 

site below the bridge (Mesta 2009, pers. 

comm.). 

Despite the increase in human 

population and associated impacts to 

the riparian habitat on which the bald 

eagle depends, the known number of 

breeding areas within the Sonoran 

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Desert Area has increased from a low of 

three in 1971 to a high of 52 in 2009, 

and the population has expanded into 

areas not previously occupied. As a 

result of this growth, the density of 

breeding areas along sections of the Salt 

and Verde Rivers has increased in 

recent years. AGFD survey data showed 

that the bald eagle population in 

Arizona continued to grow during 

approximately the same time period that 

Arizona experienced a 394 percent 

increase in human population (e.g., 

from 1960 to 2000). While the 

magnitude of the effects described above 

may be moderate in localized areas, they 

are not occurring at all breeding areas or 

throughout the range of the Sonoran 

Desert Area population of the bald 

eagle. In addition, the eagle population 

has continued to increase at the same 

time that urbanization and the loss of 

riparian habitat have increased. 

Therefore, the urbanization and loss of 

riparian habitat are not affecting bald 

eagles at such a scale or magnitude that 

they constitute a threat at the 

population level. 

At this time, there is no indication of 

additional or new impacts to riparian 

areas that would accelerate or increase 

the current pressures to riparian habitat 

beyond what is currently occurring. 

Based upon what we know about how 

impacts to these key features can affect 

bald eagles, it would not be 

unreasonable to anticipate that if there 

is continued degradation of habitat, 

especially key features such as trees, at 

some point reproductive performance or 

breeding area occupancy could be 

affected. At what point and to what 

extent continued human population 

growth, associated resource use, and 

degradation of riparian habitat will 

manifest itself in effects to the Sonoran 

Desert Area population of the bald eagle 

is unknown. Unlike species with a 

narrow habitat requirement, the bald 

eagle uses broader landscapes, and as a 

result, some change to habitat is not 

expected to impede their ability to 

adjust and use the available landscape 

features successfully. As a result, the 

best available information does not 

suggest the increase in human 

population occurring in Arizona now 

and predicted to continue into the 

future will result in declines to the 

Sonoran Desert Area population of the 

bald eagle. 

Loss of Surface Flows From 

Groundwater Pumping and Surface 

Water Diversions 

Increased urbanization and 

population growth also results in an 

increase in the demand for water and, 

therefore, water development projects. 

American Rivers (2006, p. 30) found 

that municipal water use in central 

Arizona increased by more than 39 

percent between 1998 and 2006, and 

that the demand for water will only 

increase as the human population 

increases. Water for development and 

urbanization is often supplied by 

groundwater pumping and surface water 

diversions from sources that include 

reservoirs and Central Arizona Project’s 

(the steward of central Arizona’s 

Colorado River water entitlement) 

allocations from the Colorado River. The 

impacts of groundwater pumping on 

surface water flows are of particular 

concern along the Salt and Verde Rivers 

(University of Arizona 2004, p. 69), as 

well as the Gila River, all of which 

occur within the Sonoran Desert Area. 

Most of the recent bald eagle breeding 

areas have become established along the 

Salt and Verde Rivers (Allison et al. 

2008, pp. 17–18), and elimination of key 

habitat elements (e.g., water, prey base, 

large trees) could affect the ability of 

bald eagles to continue to reproduce and 

expand along these river systems. 

The Verde River was identified as one 

of the country’s most endangered rivers 

of 2006 (American Rivers 2006, pp. 30– 

31) due to groundwater pumping. As a 

result of rapidly growing communities 

in Arizona, groundwater pumping has 

caused portions of the Verde River to 

have limited or no flow during portions 

of the year (Stromberg et al. 1996, pp. 

113, 124–128; Rinne et al. 1998, p. 9; 

Voeltz 2002, pp. 45–47, 69–71). 

Specifically, more than 6 miles of 

perennial stream segments on the Verde 

River have been lost since 

approximately 1950, and water levels 

near Sullivan Lake in the headwaters of 

the Verde River have declined by greater 

than 80 feet since 1947 (Wirt 2006, pp. 

5–6). 

Because of increasing demands for 

water and decreasing groundwater 

levels, the State Legislature adopted the 

Arizona Groundwater Management Act 

(A.R.S. § 45–555) in 1980. The Arizona 

Groundwater Management Act 

designated four Active Management 

Areas where groundwater supplies are 

critical or imperiled for whole or 

multiple groundwater basins. The 

Arizona Groundwater Management Act 

limits existing uses of groundwater 

within an Active Management Area, and 

restricts new uses (Marder 2009, p. 183). 

The City of Prescott is out of compliance 

with the Arizona Groundwater 

Management Act, and, in order to 

achieve compliance, has had to secure 

new resources, teaming up with Prescott 

Valley in developing a plan to pump 

water from the Big Chino Aquifer. This 

plan and the associated well field 

development and water transfer is 

commonly known as the Big Chino 

Ranch Project. In 1992, the Arizona 

Legislature adopted A.R.S. 45–555(E), 

which explicitly authorizes the City of 

Prescott to pump up to 14,000 acre-feet 

per year from the Big Chino Aquifer. In 

addition, the town of Chino Valley has 

plans for their own groundwater 

pumping, which would be located in 

the Big Chino aquifer, and would allow 

the development of approximately 

20,000 new homes (Marder 2009, pp. 

183–187). 

Many scientists, conservationists, and 

water providers, such as the Salt River 

Project, are in agreement that 

groundwater pumping has already had 

an impact on the Verde River and that— 

given the plans of Prescott, Prescott 

Valley, and Chino Valley—further 

reductions in the Verde River instream 

flows are inevitable (Marder 2009, p. 

187). The proposed groundwater 

pumping and inter-basin transfer project 

is projected to deliver 2.8 billion gallons 

of groundwater annually from the Big 

Chino sub-basin aquifer to the rapidly 

growing area of Prescott Valley for 

municipal use (McKinnon 2006, p. 1). It 

is estimated that 80 to 85 percent of base 

flow in the upper Verde River comes 

from the Big Chino aquifer, and it is 

possible that that these groundwater 

withdrawals could dewater the upper 24 

miles of the Verde River (Wirt and 

Hjalmarson 2000, p. 44; Wirt 2005, p. 

G7; Blasch et al. 2006, updated 2007, 

pp. 1–2). The loss of water on the upper 

Verde River would affect fish 

populations and consequently 

productivity in at least one bald eagle 

breeding area (Driscoll et al. 2006, p. 

15). 

The effects of large-scale groundwater 

pumping associated with the proposed 

Big Chino Water Ranch Project and its 

associated 30-mile pipeline have yet to 

be realized in the Verde River. It is 

uncertain that this project will occur 

given the legal and administrative 

challenges it faces; however, Prescott, 

Prescott Valley, and Chino Valley have 

invested millions of dollars in planning 

and property acquisition, and the 

pumping has already been authorized 

by State law. In 2009, a Memorandum 

of Understanding was signed between 

the Town of Chino Valley and the 

Service that may help to mitigate some 

of the impacts of their groundwater 

withdrawals in the future. The Town of 

Chino Valley has agreed that, as it 

develops its water development plan, it 

will confer with the Service to assess 

potential impacts to the Verde River and 

its native species and habitats, and will 

cooperate with the Service to remove or 

reduce impacts (Service 2009, p. 2). 

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Additional groundwater withdrawal 

projects that may affect the Verde River 

include developments associated with 

the proposed consolidation of 

checkerboard land ownership in the Big 

Chino Valley. Authorized by Title I of 

Public Law 109–110 in November 2005, 

the Yavapai Ranch Limited Partnership 

will acquire 15,400 acres of land within 

Prescott National Forest in the Big 

Chino Valley, consolidating private 

ownership of 30,440 acres. At full 

buildout, the development could result 

in water use of an additional 1,039 acrefeet pumped from the Big Chino aquifer. 

Existing groundwater withdrawals for 

the Big Chino sub-basin between 1990 

and 2003 averaged 11,840 acre-feet 

(Blasch et al. 2006, updated 2007, p. 82). 

Those withdrawals—in conjunction 

with proposed pumping from the City of 

Prescott, Town of Prescott Valley, and 

the Yavapai Ranch—would exceed the 

total rate of recharge to the Big Chino 

aquifer of approximately 21,500 acrefeet. 

The middle Verde River has 

experienced low flows that have at 

times resulted in only 5,982 acre-feet of 

runoff into Horseshoe reservoir, 

considerably less than the normal of 

7,478 acre-feet (Verde Natural Resources 

Conservation District 1999, p. 1). 

Multiple diversions and groundwater 

pumping are likely contributing to low 

flows in this portion of the Verde River 

(Miller 1961, pp. 398–399; Owen-Joyce 

and Bell 1983, pp. 33–37; Sullivan and 

Richardson 1993, pp. 96, 124; Stromberg 

1993, p. 101; Glennon and Maddock 

1994, pp. 578–585; Glennon 1995, pp. 

133–134; Tellman et al. 1997, pp. 46– 

49). 

In Tonto Creek, which feeds into 

Roosevelt Lake on the Salt River, 

groundwater pumping is one of the 

factors that contribute to a loss of 

surface flows during part of the year 

between the winter and spring runoff 

and summer monsoon (Abarca and 

Weedman 1993, p. 2). However, Tonto 

Creek supports only two bald eagle 

breeding areas, both of which continue 

to produce young on a regular basis. In 

addition, the adults from one of these 

breeding areas may acquire additional 

resources from Roosevelt Lake during 

years of high water or during the winter 

(Service 2003, p. 63). 

Groundwater pumping has also led to 

identification of the Gila River as the 

nation’s seventh most endangered river 

in 2008 (American Rivers 2008, p. 33). 

Congress, through the Arizona Water 

Rights Settlement Act of 2004 (Pub. L. 

108–451, 118 Stat. 3478, December 10, 

2004), allocated up to $128 million for 

implementation of water projects 

designed to meet New Mexico’s future 

water needs (NMISC 2006, pp. 6–7). The 

State of New Mexico must provide 

notice to the Secretary of the Interior by 

December 2014 whether or not it will 

use the allocation to develop water 

projects. 

The New Mexico Interstate Stream 

Commission has proposed a project that 

would divert up to 14,000 acre-feet of 

water from the Gila River and its 

tributary, the San Francisco River, 

annually. The project would also 

require a diversion structure, pumping 

station, power station, a pipeline or 

canal system, and potentially an offsite 

dam and reservoir. The amount of water 

diverted would negatively affect 

groundwater wells, impair the river’s 

natural flows, impede the growth of 

riparian vegetation, and negatively 

affect native fish and birds (American 

Rivers 2008, p. 33). While existing water 

rights of the San Carlos Apache Tribe 

would ensure that adequate flows 

remain in the Gila River to allow for the 

San Carlos Reservoir in Arizona to be at 

least partially filled, a reduction in 

flows would mean that less water would 

be available for storage in the reservoir, 

and, consequently, less water would be 

released from the reservoir into areas on 

the Gila River downstream of the 

reservoir. 

Decreased flows from the reservoir 

could negatively affect the prey base 

(fish) and habitat for the three bald eagle 

breeding areas located downstream. 

However, it is important to note that the 

adults at only two of these breeding 

areas rely solely on free-flowing sections 

of the Gila River for foraging resources, 

and neither of them has ever produced 

young (Allison et al. 2008, pp. 17–18). 

The adults at the third breeding area use 

the San Carlos Reservoir as their 

primary foraging area and are less likely 

to be affected by decreased flows in the 

Gila River. 

The construction and management of 

reservoirs may result in adverse effects 

to the river ecosystem. However, the 

presence of reservoirs, dams, or 

regulated river reaches did not appear to 

have a negative effect on bald eagle 

reproduction in a sample of 21 bald 

eagle territories studied in Arizona in 

the 1980’s (Hunt et al. 1992, p. A-iv). 

The presence and management of 

reservoirs can lead to sediment 

entrapment, reductions in total annual 

flow and annual flood peaks, changes in 

the timing and size of high and low 

flows, altered surface area due to water 

releases, and altered short-term 

fluctuations. These in turn cause 

changes to plant species, including a 

loss of some species, and a decrease in 

recruitment of new vegetation (Service 

2002, pp. I9–I12). However, eagle 

populations have not been shown to 

decline as a result of reservoirs, and 

may even benefit over the long term. For 

example, some reservoir storage has also 

created habitat for bald eagles in places 

where they may not have occurred, even 

before large-scale human development. 

Reservoirs provide additional habitat 

diversity, especially in a desert 

ecosystem, and may create a more stable 

food source for bald eagles during the 

winter months due to congregations of 

waterfowl. The creation of reservoirs 

usually coincides with the introduction 

of exotic species of fish, some of which 

(e.g., catfish, bass, carp) can deplete 

native fishes. However, these exotic 

species make up a large portion of bald 

eagle diets in the Sonoran Desert Area, 

both in Arizona and Sonora (Hunt et al. 

1992, pp. A25–A26; Hunt et al. 2002, 

pp. 249–251). 

Similarly, eagle populations do not 

necessarily decline as a result of 

changes in vegetation due to the 

presence or management of reservoirs. 

Downstream from reservoirs, regulated 

flows have caused declines of riparian 

cottonwood and willow forests 

throughout the western United States 

(Service 2002, p. I12). The timing of 

water releases from many dams has also 

impeded riparian regeneration, 

destroyed riparian habitat and stream 

banks, and can influence the 

abundance, distribution, and diversity 

of fish species (Stromberg et al. 1996, p. 

114; Poff et al. 1997, pp. 769–770). 

Although the persistence of riparian 

trees is not a management concern in 

most breeding areas upstream of dams 

or where appropriate cliffs are available, 

within some breeding areas located 

below dams, existing trees have become 

old, are dying, and are not being 

replaced (AGFD 2008, p. 9). This is in 

part due to modification of flood 

regimes by dams, which leads to a lack 

of sediment deposition, seed dispersal, 

and timing of flows adequate for seed 

germination. 

When reservoir management leads to 

reduced surface area by releasing water 

and lowering the level of the reservoir, 

bald eagles established there may have 

fewer perches for foraging, loafing, 

feeding, and display (Stalmaster 1987). 

Similar impacts may also occur in 

Mexico, where water for agriculture is 

supplied through dams, specifically 

timed water releases, diversions, and 

surface water pumping (Driscoll and 

Mesta 2005, in prep.). Inundation from 

dams and reservoirs can have similar 

impacts, and can also eliminate 

spawning fish runs and remove nest 

sites, foraging areas, and gravel bars that 

accumulate carrion (Hunt et al. 1992, p. 

A46). The continuous drop of lake 

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levels at Roosevelt Lake from almost 100 

percent storage capacity to near 10 

percent between 1993 and 2001 was 

shown to have a negative effect on 

productivity at five bald eagle breeding 

areas that relied on the lake for foraging 

resources (Service 2003, pp. 65–67). Yet 

even with the drop in lake size, 

occupancy rates remained high, and 

young continued to be produced from 

the affected breeding areas. On the 

Verde River below Bartlett Reservoir, 

the release of cold water from the 

reservoir and other management 

activities contributed to this area’s 

having the greatest increase in the 

number of bald eagle breeding areas in 

Arizona from 1994 to 2002 (Service 

2003, pp. 72–73). Therefore, the best 

available information suggests that 

reservoir management may result in 

short-term, localized impacts to some 

bald eagle breeding areas in the Sonoran 

Desert Area by negatively affecting 

productivity, but these impacts are not 

resulting in a reduction of the eagle 

population. 

Congress passed the Arizona Water 

Settlement Act approving the Gila River 

Indian Community Water Rights 

Settlement Agreement in 2004. In 2005, 

the Secretary of the Interior signed the 

Gila River Indian Community Water 

Rights Settlement Agreement 

confirming the Community’s claim to 

653,500 acre-feet of water per 10-year 

period, providing Federal funding for 

water development projects, assuring 

rights to use existing water delivery 

systems, and adding protections for the 

Community’s groundwater supplies 

(DOI 2005, p. 4; ADWR 2006, p. 3–2). 

Potential projects to be developed, and 

the impacts any projects are likely to 

have on the Gila River, are not yet 

known; however, passage of the law in 

2004 and development of the Gila River 

Indian Community Water Rights 

Settlement Act make certain that some 

level of diversion or pumping will occur 

in the future. We do not anticipate that 

such projects would have a populationlevel effect on the Sonoran Desert Area 

bald eagle population. As mentioned 

above, there are only two bald eagle 

breeding areas that rely solely on freeflowing sections of the Gila River for 

foraging resources, and neither of them 

has ever produced young (Allison et al. 

2008, pp. 17–18). 

In the Sonoran Desert Area, flood 

control has led to channelization, bank 

stabilization, and levees. These 

engineering activities affect riparian 

systems by preventing overbank 

flooding, reducing the extent of the 

floodplain, reducing water tables 

adjacent to streams, increasing stream 

velocity and the intensity of extreme 

floods, and generally reducing the 

volume and width of wooded riparian 

habitats (Szaro 1989, pp. 77–80; Poff et 

al. 1997, pp. 769–770). Southwestern 

streams are known for their ‘‘flashy’’ 

(i.e., rapid changes in water levels 

following heavy rains) hydrology. In the 

past 30 years, 100-year flood events 

have occurred twice in Arizona, in 1983 

and 1993. Other major floods occurred 

in Arizona in 1926, 1942, 1962, 1966, 

1970, and 1974 (Arizona Geological 

Survey 1984, p. 1; USGS 1989, pp. 1– 

2; Arizona Geological Survey 1993, p. 

1). This flooding history may be an 

indication that similar events are likely 

to occur in the Sonoran Desert Area in 

the foreseeable future, and, as a result, 

flood control measures will also likely 

continue to be implemented. These 

flood control measures and their 

associated impacts to riparian systems 

can decrease the amount of suitable 

habitat available to bald eagles for 

perching and nesting. On the other 

hand, the creation of berms, dams, and 

diversions has benefited some breeding 

pairs of bald eagles in the Sonoran 

Desert Area by making prey species 

more available, but these activities, in 

addition to water table pumping on 

rivers and creeks with limited flow, 

could at the same time be making prey 

species less available by reducing the 

size of bald eagle foraging areas (Driscoll 

et al. 2006, pp. 14–15). 

A decrease in, or complete loss of, 

surface flows within portions of the 

Verde, Salt, or Gila Rivers could result 

in a loss of riparian habitat and a 

reduction or loss of prey (e.g., fish) at a 

localized level (for the affected breeding 

areas). The breeding areas associated 

with the Verde River are responsible for 

22 percent of the total productivity 

within the Sonoran Desert Area. 

Because of the importance of river 

systems, particularly the Verde River, to 

the Sonoran Desert Area population of 

the bald eagle, accurately quantifying 

the potential effects of lost surface flows 

at the population level would be 

valuable. Statistical methods can be 

used to quantitatively estimate 

population growth and extinction 

probabilities for a species under 

different demographic and 

environmental scenarios. The simplest 

type of model to perform this can be 

referred to as a simple population 

viability analysis (PVA). A simple PVA 

quantitatively estimates population 

growth and extinction probabilities for a 

single population (Dennis et al. 1991, p. 

116). The only PVA analyzing the 

potential impacts from the loss of 

surface flows to the Sonoran Desert Area 

population of the bald eagle was 

conducted in 2009. The Service used a 

PVA to analyze the potential impact that 

complete loss of surface flows on the 

upper Verde River would have on bald 

eagles breeding in the Sonoran Desert 

Area of Arizona. The preliminary results 

of this analysis indicated that, even with 

the hypothetical loss of breeding areas 

along the Verde River, the bald eagle 

population as a whole would remain 

stable (Millsap 2009, in prep.). This 

suggests that the loss of surface flows 

within portions of the Verde River may 

be a threat of moderate magnitude at a 

localized or regional scale, but the 

impact to Sonoran Desert Area bald 

eagles at the population level is 

predicted to be low. 

Summary of Factor A 

The Service has identified potential 

threats to the Sonoran Desert Area 

population of the bald eagle from the 

present or threatened destruction, 

modification, or curtailment of the 

Sonoran Desert Area population of the 

bald eagle. These threats include the 

degradation and loss of riparian habitat 

and the loss of surface flows from 

groundwater pumping and surface water 

diversions. There is little doubt that the 

human population in Arizona, 

specifically within areas occupied by 

bald eagles, will continue to grow into 

the future. Associated with this growth, 

there will likely be an increase in 

development and modifications to some 

of the habitat on which bald eagles 

depend for nesting, roosting, perching, 

and foraging. 

Although available information 

indicates that urban and rural 

development, livestock grazing, 

groundwater pumping, and surface 

water diversions have likely resulted in 

historical and continued loss of habitat 

and negative impacts to specific 

breeding areas or individual eagles, 

there is no indication that ongoing 

impacts are affecting the Sonoran Desert 

Area population of the bald eagle at the 

population level. Thus, they are not 

significantly contributing to the risk of 

extinction of the population. 

B. Overutilization for Commercial, 

Recreational, Scientific, or Educational 

Purposes 

We do not have any evidence of risks 

to the Sonoran Desert Area population 

of the bald eagle from overutilization for 

commercial, scientific, or educational 

purposes, and we have no information 

to indicate that this factor will become 

a threat to the species in the future. 

C. Disease or Predation 

We do not have any evidence of risks 

to the Sonoran Desert Area population 

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of the bald eagle from disease or 

predation, and we have no information 

to indicate that this factor will become 

a threat to the species in the future. 

D. Inadequacy of Existing Regulatory 

Mechanisms 

Under this factor, we examine 

whether existing regulatory mechanisms 

are inadequate to address the threats to 

the Sonoran Desert Area population of 

the bald eagle discussed under Factors 

A and E. Section 4(b)(1)(A) of the 

Endangered Species Act requires the 

Service to take into account ‘‘those 

efforts, if any, being made by any State 

or foreign nation, or any political 

subdivision of a State or foreign nation, 

to protect such species * * *.’’ We 

interpret this language to require the 

Service to consider relevant Federal, 

State, and Tribal laws, plans, 

regulations, Memoranda of 

Understandings (MOUs), Cooperative 

Agreements, and other such 

mechanisms that may minimize any of 

the threats we describe in threat 

analyses under all five factors, or 

otherwise enhance conservation of the 

species. We give strongest weight to 

statutes and their implementing 

regulations, and management direction 

that stems from those laws and 

regulations. An example would be the 

terms and conditions attached to a 

grazing permit that describe how a 

permittee will manage livestock on a 

BLM allotment. They are 

nondiscretionary and enforceable, and 

are considered a regulatory mechanism 

under this analysis. Other examples 

include State governmental actions 

enforced under a State statute or 

constitution, or Federal action under 

statute. Some other agreements (MOUs 

and others) are more voluntary in 

nature; in those cases we analyze the 

specific facts for that effort to ascertain 

the extent to which it can be relied on 

in the future, and how effective it is, 

and will continue to be, at mitigating 

the threat. 

Having evaluated the significance of 

the threat as mitigated by any such 

conservation efforts, we analyze under 

Factor D the extent to which existing 

regulatory mechanisms are inadequate 

to address the specific threats to the 

species. Regulatory mechanisms, if they 

exist, may preclude the need for listing 

if we determine that such mechanisms 

adequately address the threats to the 

species such that listing is not 

warranted. Within its distribution in the 

Sonoran Desert Area, the bald eagle 

occurs on lands managed by a myriad of 

Federal and State agencies, Native 

American tribes, local municipalities, 

and private lands. In this section, we 

review existing State and Federal 

regulatory mechanisms to determine 

whether they effectively reduce or 

remove threats to the Sonoran Desert 

Area population of the bald eagle. 

Specifically, the regulatory mechanisms 

discussed below address some of the 

effects to bald eagles from the direct 

take of individuals, as well as the 

indirect take through disturbance, loss 

of riparian habitat, and development. 

Federal laws and regulatory 

mechanisms protecting bald eagles 

throughout the United States include 

the Migratory Bird Treaty Act (MBTA, 

16 U.S.C. 703–712), Bald and Golden 

Eagle Protection Act (BGEPA, 16 U.S.C. 

668 et seq.), Executive Order 13186, the 

Lacey Act Amendments of 1981 (16 

U.S.C. 3372–3378), Section 404 of the 

Clean Water Act (CWA, 33 U.S.C. 1251 

et seq.), Fish and Wildlife Coordination 

Act (16 U.S.C. 661–666c), National 

Environmental Protection Act (NEPA, 

42 U.S.C. 4321 et seq.) and the 

Convention on International Trade in 

Endangered Species of Wild Fauna and 

Flora (CITES). For more information 

regarding these regulatory mechanisms, 

please refer to the February 16, 2006, 

Federal Register notice (71 FR 8238) 

reopening the comment period on the 

proposed rule to delist the bald eagle in 

the lower 48 States. Below we 

summarize the protections provided to 

bald eagles under the NEPA, MBTA, 

BGEPA, and CWA. 

All Federal agencies are required to 

comply with NEPA for projects they 

fund, authorize, or carry out. 

Additionally, activities on non-Federal 

lands are subject to NEPA if there is a 

Federal nexus, such as permitting by the 

U.S. Army Corps of Engineers or the 

Federal Energy Regulatory Commission. 

The Council on Environmental Quality’s 

regulations for implementing NEPA (40 

CFR parts 1500–1518) state that 

environmental impact statements shall 

include a discussion on the 

environmental impacts of the various 

project alternatives (including the 

proposed action), any adverse 

environmental effects that cannot be 

avoided, and any irreversible or 

irretrievable commitments of resources 

involved (40 CFR part 1502). The NEPA 

itself is a disclosure law that provides 

an opportunity for the public to submit 

comments on the particular project and 

propose other conservation measures 

that may directly benefit listed or 

sensitive fish and wildlife species; 

however, it does not require subsequent 

minimization or mitigation measures by 

the Federal agency involved. Although 

Federal agencies may include 

conservation measures for listed species 

as a result of the NEPA process, there is 

no requirement that impacts to the 

Sonoran Desert Area population of the 

bald eagle from actions analyzed under 

NEPA would be precluded. Any such 

measures are typically voluntary in 

nature and are not required by the 

statute. 

The MBTA implements various 

treaties and conventions between the 

United States and other countries and, 

unless permitted by regulations, it 

provides that it is unlawful to pursue; 

hunt; take; capture; kill; possess; offer to 

sell, barter, purchase, deliver; or cause 

to be shipped, exported, imported, 

transported, carried, or received any 

migratory bird, part, nest, egg, or 

product, manufactured or not. The 

BGEPA, originally passed in 1940, 

prohibits the take, possession, sale, 

purchase, barter, offer to sell, purchase, 

or barter, transport, export or import, of 

any bald or golden eagle, alive or dead, 

including any part, nest, or egg, unless 

allowed by permit. ‘‘Take’’ is defined as 

to ‘‘pursue, shoot, shoot at, poison, 

wound, kill, capture, trap, collect, 

molest or disturb’’ a bald or golden 

eagle. To provide a consistent 

framework in which to implement the 

BGEPA after bald eagle delisting, on 

June 5, 2007, the Service clarified its 

regulations implementing the BGEPA 

(72 FR 31132). These modifications to 

the implementing regulations for the 

BGEPA established a regulatory 

definition of ‘‘disturb,’’ a term 

specifically prohibited as ‘‘take’’ by the 

BGEPA. 

As per the regulatory definition, 

‘‘disturb’’ means to ‘‘agitate or bother a 

bald or golden eagle to a degree that 

causes, or is likely to cause, based on 

the best scientific information available, 

injury to an eagle; a decrease in its 

productivity, by substantially interfering 

with normal breeding, feeding, or 

sheltering behavior; or nest 

abandonment, by substantially 

interfering with normal breeding, 

feeding, or sheltering behavior.’’ The 

BGEPA was initially designed to protect 

eagles from intentional take, and 

lawfully permit intentional take for such 

purposes as education, depredation, 

research, and Native American religious 

purposes. However, the regulatory 

definition of ‘‘disturb’’ described above 

may have the added benefit of providing 

indirect protection of bald eagle habitat 

(e.g., if destruction of habitat results in 

disturbance). 

In 2009, the Service promulgated new 

permit regulations under the authority 

of the BGEPA for the limited take of 

bald eagles and golden eagles ‘‘for the 

protection of * * * other interests in 

any particular locality’’ where the take 

is compatible with the preservation of 

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the bald eagle and the golden eagle, is 

associated with and not the purpose of 

an otherwise lawful activity, and cannot 

practicably be avoided (74 FR 46836). 

The Service has interpreted ‘‘compatible 

with the preservation of the bald and 

golden eagle’’ to mean allowing take 

that is consistent with the goal of stable 

or increasing breeding populations. We 

will evaluate permit applications based 

on whether: (1) The take is necessary to 

protect a legitimate interest in a 

particular locality; (2) the take is 

associated with, but is not the purpose 

of the activity; (3) the take cannot 

practicably be avoided (or for 

programmatic authorizations, the take is 

unavoidable); and (4) the applicant has 

minimized impacts to eagles to the 

extent practicable, and for programmatic 

authorizations, the taking will occur 

despite application of Advanced 

Conservation Practices developed in 

coordination with the Service. Although 

the effects of implementing these 

regulations have not been realized, the 

Service’s goal of a stable or increasing 

breeding population of bald and golden 

eagles indicates a commitment to their 

conservation and management into the 

future. 

As discussed earlier in this document, 

bald eagle activities such as nesting, 

perching, roosting, and foraging in the 

Sonoran Desert Area occur from and in 

the large woody tree component of the 

riparian habitat found along rivers and 

streams, and section 404 of the CWA 

regulates fill in wetlands and streams 

that meet certain jurisdictional 

requirements. Activities that result in 

fill of jurisdictional wetland and stream 

habitat require a section 404 permit. The 

Service can review permit applications 

and provide recommendations to avoid 

and minimize impacts and to 

implement conservation measures for 

fish and wildlife resources, including 

the bald eagle. However, incorporation 

of Service recommendations into 

section 404 permits is at the discretion 

of the U.S. Army Corps of Engineers. In 

addition, not all activities in wetlands 

or streams involve fill, and not all 

wetlands or streams fall under the 

jurisdiction of the U.S. Army Corps of 

Engineers. Regardless, earlier in this 

finding we evaluated threats to the 

Sonoran Desert Area population of the 

bald eagle where effects to riparian 

habitat may occur. We found no 

information indicating that the 

degradation or loss of riparian habitat is 

acting on the species to the point that 

the species itself may be at risk, nor is 

it likely to become so in the future. 

In Mexico, the bald eagle is listed at 

the species level as ‘‘En Peligro de 

Extincion,’’ or In Danger of Extinction, 

by the Secretaria de Medio Ambiente y 

Recursos Naturales (SEDESOL 2001, p. 

20). Species in danger of extinction are 

‘‘those whose areas of distribution or 

size of their populations in the national 

territory have diminished drastically 

putting at risk their biological viability 

in their entire natural habitat, due to 

factors such as the destruction or drastic 

modification of the habitat, 

unsustainable exploitation, disease or 

depredation, among others’’ (SEDESOL 

2001, p. 4). This classification coincides 

partly with the International Union for 

Conservation of Nature’s categories of 

‘‘in critical danger’’ and ‘‘in danger of 

extinction.’’ This designation prohibits 

taking of the species, unless specifically 

permitted, as well as any activity that 

intentionally destroys or adversely 

modifies its habitat. Additionally, in 

1988, the Mexican Government passed 

the General Law of Ecological 

Equilibrium and Environmental 

Protection that is similar to NEPA in the 

United States. This Mexican statute 

requires an environmental assessment of 

private or government actions that may 

affect wildlife or their habitat. However, 

while these laws in Mexico prohibit 

intentional destruction or modification 

of the bald eagle’s habitat, they do not 

appear to be adequate to preclude 

impacts to the species’ habitat. 

Currently, we know of no regulatory 

mechanisms or conservation planning 

in place that specifically targets the 

conservation of bald eagle habitat in 

Mexico. Legislation in Mexico has 

removed regulations that promoted 

intact protection of important riparian 

and aquatic habitats. Based upon the 

lack of conservation detected through 

existing regulations over the last 20 

years of monitoring bald eagles in the 

mainland of Sonora, we anticipate there 

will continue to be future limitations to 

the regulatory mechanisms in Mexico. 

Despite concerns expressed through 

an apparent lack of adequate protection 

for the bald eagle in Mexico, Federal 

regulatory mechanisms in place in the 

Sonoran Desert Area in Arizona, where 

most of the breeding areas are located, 

appear to be adequate to alleviate some 

of the threats to the population. The 

apparent lack of protection for bald 

eagles in Mexico may contribute to 

localized or regional impacts to bald 

eagle breeding areas in that country. 

However, these impacts only have the 

potential to affect the eight known 

breeding areas located in Mexico, which 

would not be sufficient to result in 

impacts at the population level. 

Summary of Factor D 

The Sonoran Desert Area population 

of the bald eagle is protected by many 

Federal laws and other regulatory 

mechanisms. Whether or not the 

population is listed under the ESA, the 

take of bald eagles in the United 

States—including the Sonoran Desert 

Area population—will continue to be 

prohibited under the MBTA, BGEPA, 

and the Lacey Act. While legislation in 

Mexico prohibits intentional destruction 

or modification of the bald eagle’s 

habitat, and prohibits take, the 

legislation does not appear to be 

adequate to preclude impacts to the 

species’ habitat. Nevertheless, even if 

this apparent lack of protection for 

habitat has impacts upon the bald eagles 

in Sonora, those impacts would only be 

localized or regional in scope, and 

would not affect the Sonoran Desert 

Area bald eagle as a population level. 

After reviewing the best available 

commercial and scientific information, 

we conclude that the inadequacy of 

existing regulatory mechanisms does 

not significantly contribute to the risk of 

extinction of the Sonoran Desert Area 

population of the bald eagle, because 

the bald eagle is protected by many 

Federal laws and other regulatory 

mechanisms and our analysis of Factors 

A and E concluded that there are no 

significant threats to the population. 

E. Other Natural or Manmade Factors 

Affecting Its Continued Existence 

Demographic Factors 

Three different demographic models 

have been completed for the bald eagle 

in Arizona; two of those models 

specifically analyzed only those bald 

eagles nesting in the Sonoran Desert 

Area of Arizona (Allison et al. 2008, pp. 

26–38; Silver and Taylor 2008, pp. 17– 

25; and Millsap 2009, in prep.). The 

analysis associated with the first model 

estimated, based on resightings of eagles 

at breeding areas, that juvenile mortality 

increased substantially over the period 

of time between 1975 and 2007. If 

juvenile mortality is at the high levels 

estimated and it stays at those levels, 

the model estimated the probability of 

extinction for the Sonoran Desert Area 

population of the bald eagle in Arizona 

by 2075 at 69.5 percent. This analysis 

assumed that juvenile mortality would 

continue to occur unabated at that level 

and concluded that, should fish 

stocking on the Salt and Verde Rivers be 

decreased or the management efforts 

carried out under the ABENWP be 

discontinued, the probability of 

extinction would be even higher. 

However, if juvenile mortality could be 

reduced to the average mortality value 

of the entire period of study, the 

extinction risk would be reduced to four 

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percent by 2075 (Silver and Taylor 

2008, pp. 2, 25–26, 52–55). 

In the Arizona-wide model, the AGFD 

conducted its own demographic 

analysis of the bald eagle in Arizona in 

2008. This analysis incorporated data 

from all breeding areas in Arizona, 

including six that were located outside 

of the Sonoran Desert Area. The model 

developed by the AGFD concluded 

that—depending on the age at first 

reproduction, sex ratios, and the 

proportion of females that breed each 

year—future annual declines in 

breeding will likely range between 3.6 

and 5.5 percent. This is consistent with 

a stable or declining population (Allison 

et al. 2008, p. ii). In the same analysis 

however, simple counts of bald eagles 

breeding in Arizona each year indicated 

that the breeding segment has been 

increasing at an average rate of 4.0 

percent per year from 1987 to 2003 

(Allison et al. 2008, p. 26). The 

discrepancies between the demographic 

model and the count-based estimates 

may reflect incorrect assumptions about 

newly discovered breeding areas, 

idiosyncrasies of their data, low 

estimates of survival, emigration, 

shifting age of first reproduction from an 

expanding population, or recruitment of 

breeders from unmarked populations. 

The AGFD concluded that their work 

did not determine whether or not the 

bald eagle population in Arizona, 

including the Sonoran Desert Area, was 

stable, but instead identified gaps in 

data that limit the ability to accurately 

predict population stability through 

demographic models (Allison et al. 

2008, pp. ii, 30–31). 

The Service reviewed the abovementioned models conducted by the 

AGFD and Silver and Taylor (2008, pp. 

17–26). A concern with these models is 

that both have led to estimates of the 

annual rate of population change (or 

replacement rate (l)) that are less than 

1.0, indicative of a declining 

population, whereas actual counts of 

occupied territories have increased 

almost annually since 1983 (Allison et 

al. 2008, p. 20). Although there are 

many factors that might contribute to 

this discrepancy, the Service believes 

the most likely factor is that juvenile 

and subadult bald eagle survival is 

underestimated. Underestimation of 

survival rates for nonbreeding age 

classes and cohorts of raptors in markrecapture studies is common (Kenward 

et al. 2000, p. 277; Millsap and Allen 

2006, p. 1396), and both Silver and 

Taylor (2008, p. 24) and Allison et al. 

(2008, pp. 14, 33) recognized this as a 

possible reason for the incongruence 

between model-based results and 

reality. This can bias results from the 

fact that most detections of marked bald 

eagles occur once birds settle on a 

territory and begin breeding. Bald eagles 

marked as nestlings do not typically 

settle on a territory for 4 years or longer, 

and probabilities of detection are 

confounded by potential for longdistance natal dispersal, rates of which 

may differ between the sexes. As 

evidence of the potential that this bias 

exists for the Arizona study, the juvenile 

and subadult annual survival rate for 

the selected model in Allison et al. 

(2008) was 73 percent. Annual survival 

estimates from studies employing radio 

or satellite telemetry, which do not have 

the same resighting bias for juvenile and 

subadult bald eagles, ranged from an 

average of 95 percent in Virginia 

(Buehler et al. 1991, pp. 610–611), to 85 

percent (Wood and Collopy 1995, pp. 

83–85) in one Florida study and 84 

percent in another (Millsap et al. 2004, 

pp. 1025–1027). 

The Service has concerns about using 

model results that are inconsistent with 

known historic population trajectories 

to evaluate extinction risk. However, we 

believe it is reasonable to conclude that 

biased juvenile and subadult survival 

rates are the main reason for the 

discrepancy, and a logical fix is to 

iteratively adjust these rates until the 

annual rate of population change 

reaches the observed value and then to 

evaluate extinction risk using models 

that incorporate these demographic 

estimates. Using the adjusted survival 

rates, in 2009 the Service developed a 

third model, which specifically 

analyzed the Sonoran Desert Area 

population of bald eagles in Arizona 

(Millsap 2009, in prep.). For the 

baseline model, productivity was set at 

0.76, nonadult survival (i.e., fledgling to 

age four) was set at 0.805, adult survival 

was set at 0.88, and the number of 

suitable breeding territories was set at 

42. Under this scenario, none of the 100 

iterations in the model resulted in 

extinction, and the annual rate of 

population change was equal to 1.02 

(i.e., the population was growing at an 

annual rate of 2 percent) (Millsap 2009, 

in prep.). 

Mortality rates of bald eagles in 

Arizona appear to be consistent with 

those reported for other populations of 

bald eagles. An average of 16 percent 

adult mortality was reported between 

1987 and 1990 (5.25 breeding adults 

annually) (Hunt et al. 1992, p. A137) for 

bald eagles in Arizona. This mortality 

rate is within the range reported for 

other populations, which ranged from 5 

to 17 percent (Allison et al. 2008, p. 25). 

Nestling mortality rates of 22.6 and 25 

percent have been reported in Arizona 

(Driscoll et al. 1999, p. 222; Allison et 

al. 2008, p. 33). In mainland Sonora, 

over 20 years of monitoring, 14 nestlings 

died (26 percent) of the 54 nestlings 

known to have hatched (Driscoll and 

Mesta 2005, in prep.). These rates are 

higher than the 15 percent reported in 

rangewide studies (Stalmaster 1987, p. 

143). However, the higher rate of 

mortality reported in Arizona may be in 

part attributable to more intensive 

monitoring and consequently better 

detection of mortalities through the 

ABENWP. Subadult survival in Arizona 

is generally lower than that reported 

elsewhere, but this should be 

considered apparent survival, since 

estimates may include losses due to 

emigration as well as mortality. 

Two adult bald eagles and two 

nestlings were discovered dead below 

nests within the mainland Sonora 

population in 1988 and 1993 (Driscoll 

and Mesta 2005, in prep.). Both of these 

dead adults are likely the result of 

aggressive interactions with other bald 

eagles. The two nestlings found dead 

were located within the crop of one of 

the dead adult eagles. In Arizona, 

intruding eagles have killed nestlings 

and fought with breeding eagles (Hunt 

et al. 1992, p. A146), and a breeding 

eagle killed and ate its own nestling 

while still in the nest (Beatty et al. 1995, 

p. 21). While the existence of these 

intruding eagles identifies the presence 

of an important ‘‘floating’’ population, 

these aggressive interactions may be a 

result of all serviceable breeding areas 

being occupied, therefore necessitating 

‘‘stealing’’ of a territory (Hunt et al. 

1992, p. A146). As a result, with only 

a few territories known to be occupied 

by bald eagles in mainland Sonora, 

these incidents could be an indication 

that additional suitable territories are 

not available. However, due to the 

difficulty of surveying and monitoring 

bald eagle nest sites in Sonora, we are 

not certain that this type of conclusion 

can be supported at this time. 

The Sonoran Desert Area population 

of the bald eagle in Arizona had a mean 

estimated productivity rate of 0.80 

between 1987 and 2003. Four other 

populations documented by Allison et 

al. (2008, p. 31) had estimates of 

productivity equal to or lower than that 

reported here, while the remainder of 

the populations had higher rates. Exact 

comparisons of productivity reported 

between studies are difficult, as 

different methods were used to measure 

productivity, and these studies occurred 

over different time periods. Studies in 

Arizona were more intensive and, 

therefore, more likely to document 

mortality of nestlings and fledglings 

beyond 8 weeks of age. This resulted in 

lower productivity and nest success 

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estimates than would be obtained under 

a conventional protocol (Allison et al. 

2008, pp. 31–32). 

In general, bald eagles in the Sonoran 

Desert Area of Arizona had lower 

fledgling success than bald eagles 

elsewhere, but this has not resulted in 

depressed productivity compared to 

other regions. The occupancy rate of 

known breeding areas in Arizona was 

about 90 percent, which is the same as 

that reported for Florida (Millsap et al. 

2004, p. 1023). These high occupancy 

rates may indicate that the populations 

are large enough to saturate available 

breeding areas (Stalmaster 1987, p. 141). 

If this is the case, further growth of the 

breeding population would be limited 

by the lack of available nesting and 

foraging habitat. However, as mentioned 

above in the Factor A discussion, the 

known number of breeding areas within 

the Sonoran Desert Area has increased 

from a low of three in 1971 to a high of 

52 in 2009, and the population has 

expanded into areas not previously 

occupied. This may indicate that the 

population has not yet reached the point 

of saturation. Allison et al. (2008, p. 32) 

noted that mechanisms such as habitat 

saturation, density dependence, or 

continuing external threats to 

productivity cannot be assumed at this 

point, and that low productivity levels 

by themselves should not be used to 

interpret the status of the species in 

Arizona. By themselves, productivity 

estimates are difficult to interpret, 

because low productivity in a 

population may indicate a population 

decline or, conversely, a recovered 

population. 

Declining Prey Base 

Appropriate prey resources are 

essential for the presence and 

distribution of bald eagle breeding areas, 

and similarly for the success of breeding 

attempts. Stalmaster (1987, p. 131) 

found that foraging areas are the most 

essential components of the habitat used 

by bald eagles, and they must provide 

an adequate amount of food in a fairly 

consistent fashion. He further noted that 

food may be abundant and nutritious, 

but if prey species are not accessible, 

they have no value to an eagle. 

Stalmaster (1987, pp. 170–171) noted 

that food must show a high level of 

continuity in its distribution, both in 

time and space, to have the maximum 

benefit. Eagles are able to fast for long 

periods; however, disruptions in prey 

abundance may cause excessive nestling 

mortality, increase susceptibility to 

disease, or reduce the general health of 

the bird. 

Bald eagles rely on aquatic 

ecosystems as a source of a continuous 

and accessible supply of fish for 

survival and reproduction (Stalmaster 

1987, pp. 159, 170–171). Dams can 

affect both the habitat and prey base of 

bald eagles by altering the flows of 

water and sediment in a stream (Service 

2002, p. I8). River damming, regulation, 

and diversion can interrupt, reduce, or 

prevent the availability of fish to bald 

eagles. Conversely, dams can provide an 

additional source of food for bald eagles 

from fish that are killed in turbines, 

float downstream, and are scavenged 

(Stalmaster 1987, pp. 131, 159). As 

mentioned above under Factor A, 

reservoirs provide additional habitat 

diversity, especially in a desert 

ecosystem, and may create a more stable 

food source for bald eagles during the 

winter months due to congregations of 

waterfowl. The creation of reservoirs 

usually coincides with the introduction 

of exotic species of fish, some of which 

(e.g., catfish, bass, carp) can deplete 

native fishes. However, these exotic 

species make up a large portion of bald 

eagle diets in the Sonoran Desert Area, 

both in Arizona and Sonora (Hunt et al. 

1992, pp. A25–A26; Hunt et al. 2002, 

pp. 249–251). 

Native fishes have been declining 

rapidly across the desert Southwest over 

the last century, and the desert aquatic 

environments in which they have 

evolved have been altered by various 

chemical, physical, and biological 

impacts. Within Arizona, populations of 

native fishes have been reduced by dam 

construction, altered flow regimes, loss 

of surface water, riparian vegetation 

degradation, and the introduction of 

various nonnative species. Introduction 

of nonnative fishes has had detrimental 

effects on native fishes through 

competition, hybridization, alteration of 

habitat, disease transfer, and predation 

(Bonar et al. 2004, p. 3; Minckley and 

Deacon 1991, pp. 15–17). As a result of 

competition and predation, nonnative 

fish have replaced native fish in many 

central Arizona rivers (Rinne and 

Minckley 1991, p. 40), and competition 

with nonnative fishes is now the most 

consequential factor preventing 

conservation and recovery of native 

fishes in the Southwest (Meffe 1985, pp. 

184–185; Minckley and Deacon 1991, 

pp. 15–17; Marsh and Pacey 2005, 

p. 62). 

Unlike bald eagles that rely primarily 

on dead and dying fish collected from 

the surface of lakes, bald eagles in the 

Sonoran Desert Area that forage 

primarily in free-flowing streams (and 

regulated stretches) rely upon capturing 

live fish (Hunt et al. 1992, p. A55). Hunt 

et al. (1992, p. A70) cited fish diversity 

as a crucial feature of suitable bald eagle 

breeding locations and native Sonoran 

and desert suckers as an important prey 

item in riverine systems. Other 

important fish species included exotic 

carp and channel catfish (Hunt et al. 

1992, A26). 

Various fish species become available 

to bald eagles as prey in different ways 

and at different times. Live fish become 

vulnerable to attack when they enter 

shallow water or swim near the surface. 

Within the Sonoran Desert Area, the 

most vulnerable species in shallow 

water are the bottom-feeders (e.g., 

Sonora sucker, desert sucker, carp, 

channel catfish, flathead catfish) 

because of their downward visual 

orientation (Hunt et al. 1992, p. A44). 

Species that spawn in shallow water 

such as carp and suckers are especially 

vulnerable. Of the 134 depth 

measurements at strike points where 

Sonoran Desert Area bald eagles 

captured fish, 70 (52 percent) were in 

water 20 cm (7.9 in) or less in depth, 

and 92 percent were in water less than 

100 cm (39.4 in) deep (Hunt et al. 1992, 

p. A55). 

Bald eagles in the Sonoran Desert 

Area are able to successfully exploit a 

wide range of prey including nonnative 

fish, but there is a specific sequence in 

the timing of prey availability such that 

one species rarely dominates the diet of 

an eagle pair throughout an entire 

breeding season. Pulses of increased 

prey availability occur throughout the 

breeding season. This diversity of their 

foraging suggests that threshold levels of 

prey, as well as habitat variation, may 

be requisite to nest site selection and 

nestling success (Hunt et al. 1992, p. 

A70). 

Within the sequencing of increased 

prey availability to bald eagles nesting 

in riparian environments within the 

Sonoran Desert Area, native Sonoran 

and desert suckers seem to be 

important, not only for how they 

become available but also for when they 

become available. Suckers often spawn 

in riffles, the shallowest of the riverine 

habitats, and may be consistently 

exposed to attack at this stage of their 

life cycle (Minckley 1973, pp. 162, 169; 

Hunt et al. 1992, p. A57). Water 

temperature is the catalyst for fish 

spawning and, therefore, also causes 

differences in timing of fish availability 

within breeding areas. For example, the 

fact that suckers spawn early and carp 

(and catfish) spawn later in the eagles’ 

breeding season may be of considerable 

advantage to nesting pairs of eagles. 

When both species are common, the 

result may be a prolonged availability of 

food for eagles (Hunt et al. 1992, p. 

A70). Suckers are the first of essential 

species to become most available to 

eagles while they are incubating eggs or 

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feeding small young. The movement of 

carp into shallow water to forage 

generally occurs seasonally after suckers 

have finished spawning (Hunt et al. 

1992, p. A70). Because an eagle’s 

foraging time is reduced due to the 

necessity of incubation or the care of 

newly hatched nestlings unable to 

regulate their own body temperature, 

the sucker’s place in the sequencing of 

available prey may be of added 

importance for successful reproduction 

for eagles relying on free-flowing and 

regulated streams. Additionally, there 

are no other fish species used by bald 

eagles within the Sonoran Desert Area 

along rivers that have the same 

spawning schedule and accessibility to 

nesting eagles. 

In the mid-1990s, an increase in 

nesting failure of previously successful 

bald eagle breeding areas along the freeflowing upper Salt River led to an 

examination of fish species diversity 

along this portion of the river. The 

introduction of predatory flathead 

catfish in the late 1970s nearly 

extirpated native fish populations, 

including previously abundant suckers. 

Flathead catfish, while available as bald 

eagle prey when smaller, grow to large 

sizes (up to 50 pounds), making them 

too large to be of use as prey. Large 

flathead catfish have also been observed 

preying upon smaller flathead catfish. 

The situation on the Salt River allowed 

observation of how the absence (or 

significant reduction) of a previously 

abundant prey species disrupted the 

temporal sequencing of prey availability 

and may have affected bald eagle 

productivity. The productivity of 

breeding areas along the upper Salt 

River decreased from the 1980s to the 

1990s, and an increase in predatory 

catfish may have contributed to this 

decline (Driscoll et al. 2006, p. 19). 

A similar trend in productivity (e.g. 

decline from the 1980s to the 1990s) 

was observed in the entire Sonoran 

Desert Area population of bald eagles 

during this time period, and it is 

possible that other factors may have 

contributed to the decline observed in 

the upper Salt River breeding areas. 

However, low productivity continues to 

occur in the upper Salt River breeding 

areas, while productivity has increased 

in other portions of the Sonoran Desert 

Area. Overall, productivity of bald 

eagles within the Sonoran Desert Area, 

even with the reductions observed in 

the upper Salt River, is consistent with 

that observed in other areas of the 

species’ range (Driscoll et al. 2006, p. 5). 

It is possible that changes in fish 

populations (among other manmade 

impacts to streams) may be affecting the 

likelihood of expansion of bald eagles 

into currently unoccupied sections of 

other Sonoran Desert Area rivers. 

On the free-flowing middle Verde 

River between Camp Verde and 

Horseshoe Lake, two previously 

productive bald eagle breeding areas are 

now observed to fail with consistency. 

For the first 39 years of their existence 

up to 1999, they were successful a 

combined 26 times. Since 2000, in a 

combined 18 nest years, they were 

successful only once (Driscoll et al. 

2006, pp. 35–36, 48–50; AGFD 2007, pp. 

33–34; AGFD 2008a, pp. 38–39). 

However, during the same time period, 

two other breeding areas located on this 

section of the Verde River have been 

successful a combined 14 times. 

Investigations into the distribution, 

abundance, and proportion of native 

and nonnative fish species along this 

length of the Verde River found native 

species the least abundant and 

nonnative the most abundant in this 

section of the Verde River. The 

conclusion for this distribution was that 

the low densities of native fish may be 

caused by continual predation since the 

early 1900s (Bonar et al. 2004, p. 3). 

Hunt et al. (1992, p. A46) also 

concluded that the rarity of suckers in 

river sections upstream of the reservoirs 

is also partially a result of sucker 

populations being overwhelmed by 

large numbers of carp and catfish from 

the reservoirs. Other predatory exotic 

fish, like smallmouth bass, may also 

contribute to the predation of native fish 

in this section of the Verde River. 

It is informative to observe where bald 

eagles have established breeding areas 

and whether there is any relationship 

between those locations and the 

locations where impacts to prey 

resources may have already occurred 

prior to the modern day monitoring of 

bald eagle territories. For example, as 

discussed above, the majority of bald 

eagle productivity in the Sonoran Desert 

Area, exclusive of Sonora, is tied to 

breeding areas along the Salt and Verde 

Rivers. The Gila River and Lower 

Colorado River within the Sonoran 

Desert Area both provide miles of river 

with similar attributes to the Salt and 

Verde Rivers (e.g., presence of largebodied fishes, cliffs and large trees for 

nesting, perennial flow, and existing 

bald eagle breeding areas). Five 

productive bald eagle breeding areas 

exist along or adjacent to these 

waterways. However, unlike the Salt 

and Verde Rivers, where eagles exist 

upstream and downstream of reservoirs, 

no bald eagle breeding areas are solely 

associated with the regulated mainstem 

Colorado River or the free-flowing Gila 

River above San Carlos Lake within the 

Sonoran Desert Area. All of their 

foraging areas are primarily associated 

with reservoirs (San Carlos Lake, 

Talkalai Lake, and Copper Basin/Gene 

Wash Reservoir). While two breeding 

areas were established along the 

regulated Gila River below Coolidge 

Dam at San Carlos Lake since the midto late-1990s, these pairs have never 

been successful (and only laid eggs five 

times) in their 23 combined nest years. 

These observed patterns and lack of 

success along the free-flowing and 

regulated sections of the Gila and 

Colorado Rivers within the Sonoran 

Desert Area are indicative that 

conditions are not conducive to 

successful nesting, and, based upon 

similar patterns observed along the 

upper Salt and Verde Rivers, lack of 

prey diversity may be a contributing 

factor. 

Similar to bald eagles in the Sonoran 

Desert Area of Arizona, fish species 

eaten by nesting eagles in Mexico are a 

combination of nonnative and native 

fishes. Identified fish found in prey 

remains collected from nests were 

nonnative channel catfish, carpsucker 

(Carpiodes carpio), carp, tilapia (Tilapia 

sp.), largemouth bass, and native Yaqui 

catfish (Ictalurus pricei) and Yaqui 

sucker (Catostomus bernardini) (Driscoll 

and Mesta 2005, in prep.). Nonnative 

species, such as bullfrogs and sport and 

bait fish, have been introduced 

throughout Mexico, and continue to 

disperse naturally, broadening their 

distributions (Conant 1974, pp. 487– 

489; Miller et al. 2005, pp. 60–61; Luja 

and Rodriguez-Estrella 2008, pp. 17–22). 

The damming and regulation of 

Mexican rivers and the addition of 

nonnative fishes are expected, over 

time, to continue to provide conditions 

favorable to nonnative fish and declines 

in native fish (Unmack and Fagan 2004, 

p. 233). 

Minckley and Miller (in Miller et al. 

2005, p. 61) noted that Mexico’s critical 

need for domestic, irrigation, and 

industrial water supplies and electrical 

power are being met through the 

impoundment of both major and minor 

rivers. They conclude that dams have 

remarkably harmful effects on riverine 

systems and native fishes, and that they 

result in the establishment of nonnative 

fishes, which is considered the single 

greatest challenge to survival of native 

fish species. Unmack and Fagan (2004, 

p. 233) noted that the current status of 

nonnative fishes in the Yaqui Basin is 

remarkably similar to what was evident 

from the Gila Basin in Arizona and that, 

without strong action, the native fish of 

the Yaqui Basin will become 

increasingly imperiled over the next 

several years. While nesting bald eagles 

can take advantage of the variety of 

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fishes along rivers, including introduced 

catfish and carp (Hunt et al. 1992, pp. 

Aii, Aiii), it is unclear to what extent 

nonnative fishes may be affecting the 

reproductive success of bald eagles in 

Mexico. 

The ‘‘Conservation Assessment and 

Strategy for the Bald Eagle in Arizona’’ 

identifies the need to concentrate efforts 

on restoring native fish populations and 

fish diversity to stabilize bald eagle 

productivity and enhanced survival 

(Driscoll et al. 2006, pp. 51–53). 

However, efforts to accomplish 

increased fish diversity along regulated 

and free-flowing streams within the 

Sonoran Desert Area are difficult, 

complex, and require considerable 

funding, time, and public support. Even 

then, there is uncertainty over their 

success. For example, stocking of 

Colorado pikeminnow and razorback 

suckers has occurred within the 

Sonoran Desert Area on the Verde, Salt, 

Gila, and lower Colorado Rivers with 

little to no success. The Service is not 

aware of any management actions 

designed to improve the diversity of 

native Sonoran or desert suckers along 

the mainstem of these rivers within the 

Sonoran Desert Area, whereas sportfish 

stocking of nonnative species such as 

catfish and largemouth bass continue to 

be widespread in Arizona. 

There is little evidence to suggest that 

without active management the balance 

of native and nonnative fish will be 

maintained or improved. At present, 

nonnative fish stocking continues with 

stocking schedules posted online, 

including schedules for stocking of the 

Salt and Verde Rivers. Each year, the 

AGFD stocks more than three million 

fish—including rainbow, Apache, 

brook, and cutthroat trout; largemouth 

bass; and channel catfish—in 

approximately 160 of Arizona’s lakes, 

rivers, and streams (AGFD 2009b, p. 1). 

The stocking program is supported with 

Federal funds through the Federal Aid 

in Sport Fish Restoration Program, along 

with State funds from the sale of 

licenses and trout stamps. The Service 

is undergoing consultation in 

coordination with AGFD on the 

proposed stocking program for the next 

10 years. The consultation will include 

an assessment of anticipated impacts of 

stocking of nonnative fish and their 

impacts on prey diversity for bald eagles 

into the future. 

Based upon continued sportfish 

stocking, we anticipate continued 

increases in nonnative fish and reduced 

abundance and distribution of native 

fish on central Arizona rivers and 

reservoirs within the Sonoran Desert 

Area. Regarding recovery of native 

fishes in the southwestern United 

States, Clarkson et al. (2005, pp. 20, 23) 

noted, ‘‘no amount of habitat restoration 

can successfully advance biological 

recovery unless preceded or 

accompanied by elimination of 

nonnatives.’’ They further noted that 

nonnative species already occupy 

reservoirs and the few natural lakes in 

the Southwest, and that it is impractical 

to eliminate these fishes from lake 

habitats. They noted that medium and 

small warm-water streams and stream 

systems may be suitable for recovery of 

native fishes. However, for the most 

part, these are not the streams that 

support bald eagles. For those pairs 

relying on prey from regulated or freeflowing streams, the loss of fish 

diversity may be causing negative 

effects to reproduction at the localized 

level. 

Despite this apparently continuing 

decrease in fish diversity, the best 

available information suggests that the 

scope and intensity of the effect this 

decrease in diversity is having or will 

have on the Sonoran Desert Area 

population of the bald eagle does not 

appear to be sufficient to result in 

population-level effects. While 

previously successful breeding areas 

located on the middle Verde River and 

upper Salt River have declined in 

productivity in recent years, these 

breeding areas continue to be occupied, 

and young are occasionally produced; 

new breeding areas and other nonriverine sites are producing eagles; and 

overall productivity rates within the 

Sonoran Desert Area are within the 

range of rates observed in other bald 

eagle populations. Therefore, after a 

review of the best available commercial 

and scientific information, we conclude 

that a declining prey base does not 

constitute a significant threat to the 

Sonoran Desert Area population of the 

bald eagle at the population level. 

Contaminants, Pollutants, and Eggshell 

Thinning 

As a barometer of environmental 

health at the top of the food chain, bald 

eagles are susceptible to impacts from 

contaminants that can accumulate in the 

bodies of fish (Newton 1979, pp. 230– 

231) and pollutants that can affect prey 

(Newton 197, p. 259). Water pollution 

was identified in a list of threats to 

aquatic biota in Mexico by Miller et al. 

(2005, pp. 60–61), and, clearly, 

contaminants such as organochlorides 

(e.g., Dichlorodiphenyldichloroethylene 

(DDE), Dichlorodiphenyltrichloroethane 

(DDT)) and heavy metals (e.g., mercury, 

lead) continue to be threats to bald 

eagles. These contaminants can 

typically be associated with agriculture, 

urbanization, mining, and other 

resource uses (Newton 1979, pp. 230, 

254–255). Similarly, pollution that kills 

or reduces fish populations directly 

affects the abundance, diversity, or 

availability of food needed for bald 

eagle reproduction. 

The AGFD and the Service analyzed 

27 addled bald eagle eggs in Arizona 

from 1994 to 2004 that showed mercury 

levels ranging from 0.55 to 8.02 parts 

per million (ppm). Of these eggs, 10 

were classified as toxic (exceeding 2.0 

ppm), 11 had elevated levels (1.5 to 2.0 

ppm), and four had lesser 

concentrations (1.0 to 1.5 ppm). The 10 

eggs classified as toxic came from 

breeding areas located on the Salt, 

Verde, and Gila Rivers and Tonto Creek 

(Driscoll et al. 2006, p. 21). While eggs 

tested for mercury were addled and did 

not produce young, successful 

production of young has occurred at all 

of these breeding areas following the 

year or years in which mercury was 

detected (viable eggs are not collected 

and tested for mercury). For example, a 

breeding area located on Tonto Creek 

had the highest ever recorded mercury 

level for eggs from Arizona in 1995, but 

the pair successfully produced young in 

1996 through 2001, 2007, and 2008. 

Assuming mercury was the cause of nest 

failure, these data indicate that high 

levels of mercury in eggs at a given nest 

site may cause nest failure for one 

season, but future reproduction may not 

be affected. 

Lead poisoning is an additional 

stressor for breeding areas within the 

Sonoran Desert Area. Lead poisoning in 

bald eagles has been linked to ingestion 

of lead gunshot, consumption of lead 

sinkers, and secondary consumption of 

lead-contaminated prey. Research 

indicates that toxic liver lead levels for 

bald eagles rangewide is somewhere 

between 6.0 and 10.0 ppm (Pattee et al. 

1981, pp. 808–809; Driscoll et al. 2006, 

p. 20). From 1998 to 2004, 22 bald 

eagles (or 39 percent of all documented 

mortalities rangewide) had liver lead 

levels averaging 32.9 ppm and ranging 

from 0 to 9 times the toxic threshold. 

Only one of the eagles confirmed to 

have lead poisoning was fledged from a 

nest in Arizona. Because bald eagles 

travel large distances, the ingestion of 

lead could occur in any area along their 

migration, making it difficult to 

determine the source of the poisoning 

(Driscoll et al. 2006, pp. 20–21). 

Organochlorides continue to be 

detected in bald eagle eggs within the 

Sonoran Desert Area, with a recent 

measurement of DDE at 4.23 ppm wet 

weight in one egg from a breeding area 

on the lower Verde River in 2002. A 

reduction in productivity is known to 

occur when DDE values in bald eagle 

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eggs are between 3 and 5 ppm (wet 

weight) (Wiemeyer et al. 1984, p. 541). 

This level has been reached in eggs 

collected from three breeding areas 

along the Verde River and one located 

on Tonto Creek. The most complete 

DDE data set over time is from a 

breeding area located on the upper 

Verde River, where DDE concentrations 

declined from 3.2 ppm in 1994 to 0.91 

ppm in 2001. Following DDE levels of 

3.20 ppm (wet weight), this breeding 

area produced young in 1996 through 

2003, and 2005 through 2007. At 

another breeding area located on the 

upper Salt River, young have been 

produced since DDE levels of 4.17 ppm 

(wet weight) were found in 2001. At one 

breeding area located on the lower 

Verde River, DDE levels of 7.00 ppm 

(wet weight) were detected from an egg 

collected in 1997, but the breeding area 

produced young in 1998, 1999, and 

2001 through 2008. Similarly, another 

breeding area in the same area, with 

DDE levels of 4.23 ppm in 2002, 

produced young in 2004 and 2006 

through 2008 (Driscoll et al. 2006, p. 

22). 

DDT is known to cause eggshell 

thinning. For bald eagles, eggshell 

thinning greater than 10 percent can 

cause difficulties in reproduction 

(Wiemeyer et al. 1984, p. 543). The 

AGFD found five separate occasions on 

which eggshell thinning in Arizona 

equaled or exceeded 10 percent between 

1993 and 2004 (Driscoll et al. 2006, p. 

23). However, the AGFD concluded that 

other factors may have a greater 

influence on productivity than DDT, but 

that egg collection and eggshell 

measurements will continue to ensure 

that the effects of DDT and other 

organochlorides are monitored. The 

Service agrees with this conclusion, and 

believes that eggshell thinning warrants 

further study and monitoring; however, 

at this time, the Service is not aware of 

any data to indicate eggshell thinning at 

the levels cited is resulting in lost 

reproduction. 

In mainland Sonora, bald eagle eggs 

collected in the late 1980s were 

analyzed for metabolized DDE. 

Organochloride levels were well below 

concentrations that reduce productivity, 

and eggshell thickness was near preDDT levels (Driscoll and Mesta 2005, in 

prep.). In addition to pesticides, other 

contaminants may be in use near bald 

eagle breeding areas in mainland 

Sonora. Gold mines are located 

sporadically along the Rio Yaqui. Many 

of the mines are old and inoperable, but 

some have been reopened, with 

strychnine used to leach gold from the 

ore. These mines are often adjacent to 

the rivers in arroyos where runoff could 

lead to stream contamination (Driscoll 

and Mesta 2005, in prep.). Based upon 

increasing human populations and 

proximity of agriculture and mining to 

rivers where eagles nest or could nest in 

the future, the current and future 

impacts of contaminants and pollution 

on bald eagle health and reproduction 

in Mexico are unknown. 

In addition to monitoring bald eagle 

eggs, the Service has been evaluating the 

effects of mercury, organochlorides, and 

other pesticides for many years. The 

AGFD and the Service have developed 

a protocol for identifying, documenting, 

and processing all bald eagle carcasses 

found in Arizona, which will allow for 

the continued monitoring of mortality 

factors, including lead poisoning and 

other contaminants. 

Based on the above information, 

contaminants, pollutants, and eggshell 

thinning have likely resulted in 

historical and continued impacts to the 

reproductive success of bald eagles in 

the Sonoran Desert Area. Specifically, 

organochlorides and mercury have been 

detected within the Sonoran Desert Area 

at levels that are known to affect 

productivity, but all of the affected 

breeding areas have continued to 

produce young. Many of these are 

among the most productive breeding 

areas located within the Sonoran Desert 

Area. Bald eagles in the Sonoran Desert 

Area are potentially exposed to 

contaminants and pollutants throughout 

their range. However, the impact from 

these threats has been of low magnitude, 

and does not persist for long periods of 

time. The best scientific information 

suggests that contaminants, pollutants, 

and eggshell thinning do not constitute 

a significant threat to the Sonoran 

Desert Area population of the bald eagle 

at the population level. 

Fishing Line and Tackle 

Fishing line and tackle have been 

found in bald eagle nests, and have 

entangled bald eagles within the 

Sonoran Desert Area of Arizona. In 

response to this problem, the AGFD 

developed a monofilament recovery 

program in 2002. Although this program 

is voluntary, it has helped to educate 

anglers and reduce the amount of 

improperly disposed monofilament. 

Fishing line entanglement is most 

frequent on the lower Verde River (19 

percent of occurrences), the upper Salt 

River (17 percent of occurrences), and 

Alamo Lake (14 percent of occurrences) 

(Driscoll et al. 2006, p. 18). Bald eagles 

encounter fishing line primarily by 

catching dead or dying fish with fishing 

line or tackle still attached, and they 

may also collect it for use as nest 

material (Hunt et al. 1992, p. A135; 

AGFD 1998, p. 5). For probable causes 

of mortality in bald eagles in Arizona 

between 1987 and 2005, monofilament 

was the cause of one adult mortality and 

two nesting mortalities (Driscoll et al. 

2006, pp. 17–18). It was ranked as the 

fifteenth most common cause of 

mortality, and responsible for 3 out of 

281 deaths, or approximately 1.1 

percent (Driscoll et al. 2006, p. 25). 

Although monofilament has been shown 

to affect bald eagles within the Sonoran 

Desert Area of Arizona, it represents a 

minor threat, because the magnitude of 

the effects to the bald eagle is small (i.e., 

representing 1.1 percent of known 

mortality). We attribute the limited 

effect that monofilament is having on 

bald eagles within the Sonoran Desert 

Area of Arizona to the active 

management of the ABENWP, which we 

anticipate will continue. Additionally, 

wildlife personnel entering nests to 

conduct annual banding are 

instrumental in removing large 

quantities of monofilament (Driscoll et 

al. 2006, p. 11). 

Climate Change 

Our analyses under the Endangered 

Species Act include consideration of 

ongoing and projected changes in 

climate. The terms ‘‘climate’’ and 

‘‘climate change’’ are defined by the 

Intergovernmental Panel on Climate 

Change (IPCC). ‘‘Climate’’ refers to the 

mean and variability of different types 

of weather conditions over time, with 30 

years being a typical period for such 

measurements, although shorter or 

longer periods also may be used (IPCC 

2007, p. 78). The term ‘‘climate change’’ 

thus refers to a change in the mean or 

variability of one or more measures of 

climate (e.g., temperature or 

precipitation) that persists for an 

extended period, typically decades or 

longer, whether the change is due to 

natural variability, human activity, or 

both (IPCC 2007, p. 78). Various types 

of changes in climate can have direct or 

indirect effects on species. These effects 

may be positive, neutral, or negative, 

and they may change over time, 

depending on the species and other 

relevant considerations, such as the 

effects of interactions of climate with 

other variables (e.g., habitat 

fragmentation) (IPCC 2007, pp. 8–14, 

18–19). In our analyses, we use our 

expert judgment to weigh relevant 

information, including uncertainty, in 

our consideration of various aspects of 

climate change. 

Seager et al. (2007, pp. 1181–1184) 

analyzed 19 computer models that used 

many different variables to estimate the 

future climatology of the Southwestern 

United States and northern Mexico in 

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response to predictions of climatic 

patterns. All but one of the 19 models 

predicted a drying trend within the 

Southwest; one predicted a trend 

toward a wetter climate. Researchers 

created 49 projections using 19 models, 

and all but 3 predicted a shift to 

increasing aridity (dryness) in the 

Southwest as early as 2021–2040. 

Recently published projections of 

potential reductions in natural flow on 

the Colorado River Basin by the mid21st century range from approximately 

43 percent by Hoerling and Eischeid 

(2007, p. 35) to approximately six 

percent by Christensen and Lettenmaier 

(2006, pp. 3727–3729). The U.S. Climate 

Change Science Program (CCSP), in a 

recent report on climate change, 

concluded for the Southwest that 

‘‘subtropical aridity is likely to intensify 

and persist due to future greenhouse 

warming’’ (CCSP 2008, p. 2). 

The anticipated effects from climate 

change in the Southwest can be 

separated into three general predictions. 

First, climate change is expected to 

shorten periods of snowpack 

accumulation, as well as lessen 

snowpack levels. With gradually 

increasing temperatures and reduced 

snowpack (due to higher spring 

temperatures and reduced winter-spring 

precipitation), annual runoff will be 

reduced (Smith et al. 2003, p. 226; 

Garfin 2005, p. 42), consequently 

reducing groundwater recharge. Second, 

snowmelt is expected to occur earlier in 

the calendar year, because increased 

minimum winter and spring 

temperatures could melt snowpacks 

sooner, causing peak water flows to 

occur much sooner than the historical 

spring and summer peak flows (Smith et 

al. 2003, p. 226; Stewart et al. 2004, pp. 

217–218, 224, 230; Garfin 2005, p. 41) 

and reducing flows later in the season. 

Third, the hydrologic cycle is expected 

to become more dynamic on average, 

with climate models predicting 

increases in the variability and intensity 

of rainfall events. This will modify 

disturbance regimes by changing the 

magnitude and frequency of floods. 

Climate change will likely cause an 

increase in river temperatures in drier 

climates. This will in turn result in 

periods of prolonged low flows and 

stream drying and an increased demand 

for water storage and conveyance 

systems (Rahel and Olden 2008, pp. 

521–522, 526). Warmer water 

temperatures across temperate regions 

are predicted to expand the distribution 

of existing aquatic nonnative species by 

providing more suitable habitat. These 

species are often tropical in origin and 

adaptable to warmer water 

temperatures. This conclusion is based 

upon studies that compared the thermal 

tolerances of 57 fish species with 

predictions made from climate models 

(Mohseni et al. 2003, p. 389). 

We are uncertain about the magnitude 

of the threat posed by climate change, 

because we do not currently understand 

all potential impacts of climate change 

on bald eagles or the human population. 

However, based on the best information 

available, we conclude that climate 

change is not a significant threat, 

because the extent to which the bald 

eagle will respond to climate change is 

unclear. We have to date not detected 

climate change-related impacts to the 

Sonoran Desert Area population of the 

bald eagle; moreover, bald eagles in the 

Sonoran Desert Area, and elsewhere 

within their range, have been shown to 

be highly adaptable (e.g., feed on a 

variety of prey, nest in many types of 

structures, breed in a variety of habitats 

throughout their range). This life-history 

trait contributes to the ability of the 

Sonoran Desert Area population of the 

bald eagle to continue to exist even 

under some of the possible effects from 

climate change. 

Human Disturbance 

Small planes and helicopters are the 

most common human activities in bald 

eagle breeding areas in Arizona (Driscoll 

et al. 2006, p. 18). From 1998 to 2005, 

low-flying aircraft were responsible for 

37.1 percent (n = 23,905) of all human 

activities and 25.3 percent (n = 1,273) of 

the significant responses (e.g., restless, 

flushed, and left the area) by a breeding 

pair. For the period from 1998 to 2005, 

significant responses to low-flying 

aircraft ranged from 10.6 percent to 44.1 

percent of all significant responses by a 

breeding pair. The potential impacts 

from an eagle responding to low-flying 

aircraft include the inadvertent cracking 

of an egg as a result of flushing an 

incubating adult or premature fledging. 

Driscoll et al. (2006, p. 18) concluded 

that, while no direct link of a nest 

failure to low-flying private aircraft has 

occurred, this activity will increase with 

the demand for tourism flights, 

especially in remote breeding areas. In 

addition to private aircraft, many 

Sonoran Desert Area breeding areas are 

located near military training routes 

used by the Department of Defense. The 

Salt River Pima-Maricopa Indian 

Community is also concerned with 

military helicopter flights disturbing 

nesting bald eagles. While high-speed 

aircraft may not disturb bald eagles 

when an appropriate buffer distance is 

maintained, noise disturbance and sonic 

booms can cause a reaction (Ellis et al. 

1991, p. 53; Grubb et al. 1997, pp. 216– 

217). 

Driscoll et al. (1999, p. 220) noted 

that, of 24 eggs (in 13 clutches) for 

which we knew the cause of mortality, 

11 involved human disturbance (over a 

7-year period). The ABENWP has 

recorded a three-fold increase in the 

average number of human activities that 

occur within 1 km (0.6 miles) of all 

monitored bald eagle breeding areas in 

the last 16 years (Driscoll et al. 2006, p. 

16). Anticipated human population 

growth, as described above, will lead to 

an increased demand in water-based 

recreation in areas currently supporting 

breeding areas. Monitoring and seasonal 

closures by the ABENWP around some 

breeding areas help to minimize these 

impacts. However, not all breeding areas 

are covered by these measures. In 

addition, disturbance from recreational 

activities may affect the ability of bald 

eagles to forage, as adults need foraging 

areas without constant human 

disturbance in order to capture prey. 

Recreation outside of nesting areas 

may limit foraging opportunities and 

affect adult, nestling, and juvenile 

survival, as well as egg production 

(Driscoll et al. 2006, p. 17). It is 

anticipated that increasing recreational 

pressures will continue to occur on the 

lower Gila River, San Carlos River, Salt 

River, Verde River, Tonto Creek, Alamo 

Lake, and Lake Pleasant. The 

‘‘Conservation Assessment and Strategy 

for Bald eagles in Arizona’’ identified 

‘human activity’ as a management 

challenge for 36 of 45 breeding areas (or 

80 percent) located within the Sonoran 

Desert Area at that time (Driscoll et al. 

2006, pp. 51–53). However, human 

activity within close proximity to nests 

does not in itself necessarily result in 

negative effects to the productivity of a 

bald eagle breeding area. 

As an example of the ability of the 

bald eagle to adapt to human activity, a 

5-year study in Florida of rural (< 5 

percent intensive human use within 

1,500 meters) and suburban (> 50 

percent intensive human use within 

1,500 meters) bald eagle nests did not 

detect a significant difference between 

the two groups in occupancy rates or 

productivity. These results suggest that 

bald eagles in their study area may have 

adapted to, or at least tolerated, 

increasing human populations and 

disturbance (Millsap et al 2004, p. 

1023). However, the authors caution 

that their results merely point out that 

some eagles can successfully coexist 

with intensive human activity, but this 

should not be interpreted to mean that 

all eagles can. Within the Sonoran 

Desert Area of Arizona, the bald eagle 

breeding areas located in closest 

proximity to the Phoenix metropolitan 

area on the lower Verde and Salt Rivers 

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are also some of the most productive 

(Allison et al. 2008, pp. 17–18). 

Therefore, we conclude that human 

disturbance is not a significant threat to 

the Sonoran Desert bald eagle 

population. 

Summary of Factor E 

We evaluated a number of other 

factors that could affect the continued 

existence of the Sonoran Desert Area 

population of the bald eagle: 

Demographic factors; declining prey 

base; contaminants, pollutants, and 

eggshell thinning; fishing line and 

tackle; climate change; and human 

disturbance. After analyzing the best 

available information regarding these 

potential threats and the data regarding 

how eagles have responded to these 

factors, we concluded that none of them 

poses a significant threat to the Sonoran 

Desert Area bald eagle at a population 

level. 

Three models have been completed 

that analyzed the future risk of 

extinction to the Sonoran Desert Area 

population of the bald eagle taking into 

consideration a number of demographic 

variables. The results of the model that 

best matched observed population 

trajectories—because it used an adjusted 

survival rate for juvenile and subadult 

eagles—suggest that the Sonoran Desert 

Area population of the bald eagle is not 

at a risk of extinction in the future. In 

addition, observed mortality rates, 

productivity, and survival rates for bald 

eagles within the Sonoran Desert Area 

are all within the range of observed 

values for other bald eagle populations 

throughout the United States. 

The availability of an adequate and 

accessible supply of prey is essential to 

the success of breeding bald eagles in 

the Sonoran Desert Area. The presence 

of reservoirs, dams, or regulated rivers 

does not appear to have had a negative 

impact on bald eagle reproduction, and 

may be providing a more stable food 

source for bald eagles than would 

otherwise be available in the Sonoran 

Desert ecosystem. Native fish 

populations have been declining in the 

Sonoran Desert Area of Arizona due to 

the introduction of nonnative fish and 

alterations to their habitat. Declining 

populations of native fish along portions 

of the Salt and Verde Rivers may be a 

factor contributing to a localized 

reduction in productivity for pairs of 

bald eagles nesting in these areas. 

However, bald eagles are capable of 

exploiting a wide range of prey species, 

and nonnative fishes make up a large 

portion of their diet within the Sonoran 

Desert Area. 

Several breeding areas within the 

Sonoran Desert Area have experienced 

high levels of mercury or 

organochlorides. The productivity of 

pairs at those breeding areas indicates 

that, while nest failure may occur when 

those levels are detected, young 

continue to be produced in subsequent 

years. Several bald eagles have died of 

lead poisoning while in Arizona, but 

only one of these eagles is known to 

have fledged from a nest in Arizona. 

The long distance traveled by migrating 

eagles could mean that the ingestion of 

lead is occurring outside of Arizona. 

The protocol developed by AGFD and 

the Service for identifying, 

documenting, and processing bald eagle 

carcasses will allow for the continued 

monitoring of mortality factors, 

including lead poisoning and other 

contaminants. Based on the best 

available information, the Service 

concludes that the effects of 

contaminants should continue to be 

monitored, but they are currently not a 

significant threat to the Sonoran Desert 

Area population of the bald eagle. 

Fishing line and tackle have been 

found in bald eagle nests, and have 

entangled bald eagles within the 

Sonoran Desert Area of Arizona. 

However, fishing line is ranked as the 

fifteenth most common cause of 

mortality, responsible for only 1.1 

percent of known mortalities. Our 

review of the best available information 

indicates that fishing line is not a 

significant threat to the Sonoran Desert 

Area population of the bald eagle. 

Bald eagles in the Sonoran Desert 

Area depend on aquatic ecosystems for 

survival, and those aquatic ecosystems 

are predicted to be at risk due to drying 

under climate change scenarios. 

Potential drought associated with 

changing climatic patterns may 

adversely affect streams, rivers, and 

reservoirs—not only reducing water 

characteristics and availability, but also 

altering food availability. These changes 

may in turn exacerbate existing threats 

to bald eagles and their habitat in the 

Sonoran Desert Area. However, to date 

no impacts to bald eagles from climate 

change have been recorded, and it is 

unclear whether the bald eagle will 

adapt to these changes or respond at a 

population level. 

Human disturbance to nesting and 

foraging bald eagles from small planes, 

helicopters, military aircraft, and 

recreational activities has occurred in 

the past, is occurring now, and will 

likely continue to occur within the 

Sonoran Desert Area. The activities of 

the ABENWP and seasonal closures of 

breeding areas have helped to mitigate 

this impact at the local level, and will 

continue to be implemented into the 

future. As stated above, there has not 

been any indication that human 

disturbance has led to the failure of bald 

eagle breeding attempts, or to 

population-level effects. 

After reviewing the best available 

commercial and scientific information, 

based on our analysis above, we 

conclude that demographic factors; a 

declining prey base; contaminants, 

pollutants, and eggshell thinning; 

fishing line and tackle; climate change; 

and human disturbance are not 

significantly contributing to the risk of 

extinction of the Sonoran Desert Area 

population of the bald eagle at the 

population level. 

Finding 

In making this finding, as directed by 

the court, we used the information 

contained in our 2010 administrative 

record which included information 

provided by the petitioners, as well as 

other information in our files, and 

otherwise available. The information we 

reviewed included information 

submitted by the public and the Tribes, 

and available published and 

unpublished scientific and commercial 

information. Additionally, we had 

information from Federal, State, and 

Tribal land managers, along with 

recognized experts in conservation and 

bald eagle biology. This 12-month 

finding reflects and incorporates 

information from our 2010 

administrative record that we received 

from the public and through 

consultation, literature research, and 

field visits. Based on the rationale 

detailed above, we find that bald eagle 

population in the Sonoran Desert Area 

is discrete from other bald eagle 

populations, but is not significant to the 

bald eagle as a whole, and therefore is 

not a valid DPS, pursuant to the DPS 

Policy (61 FR 4722). 

Next, we reviewed our 2010 

administrative record regarding the past, 

present, and future threats faced by the 

Sonoran Desert Area population of the 

bald eagle. This status review identified 

threats to the Sonoran Desert Area 

population of the bald eagle under 

Factors A and E. The primary threats to 

the Sonoran Desert Area population of 

the bald eagle—the activities that the 

population has responded to most 

significantly—are from the degradation 

and loss of riparian habitat and the loss 

of surface flows from groundwater 

pumping and surface water diversions 

(Factor A). In the Sonoran Desert Area, 

bald eagle breeding areas are located in 

close proximity to a variety of aquatic 

sites, including reservoirs, regulated 

river systems, and free-flowing rivers 

and creeks. The essential components of 

these sites for bald eagles are the 

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availability of trees for roosting, 

perching, hunting, and nesting, and 

access to prey, primarily fish. The 

decline of riparian habitat stems 

specifically from direct loss from 

development and indirect impacts from 

the loss of surface flows. 

With respect to each kind of threat, 

the best available information has 

confirmed a response to the threat, such 

as a decrease in breeding rates or 

survival rates. However, the potential 

for population-level impacts to bald 

eagles throughout their range— 

including in the Sonoran Desert Area— 

from the degradation or loss of riparian 

habitat and the loss of surface flows 

from groundwater pumping and surface 

water diversions has been reduced by 

the regulatory mechanisms in place 

within the United States and locally, the 

strong ability of bald eagles to adapt to 

changes in their environment, the 

widespread distribution of bald eagles 

along rivers within the Sonoran Desert 

Area, and the availability of reservoirs. 

Additional potential threats to the 

Sonoran Desert Area population of the 

bald eagle include demographic factors; 

declining prey base; contaminants, 

pollutants, and eggshell thinning; 

fishing line and tackle; climate change; 

and human disturbance. However, 

based on the best available information 

none of these poses a significant threat 

at a population level. 

We must also evaluate whether these 

combined potential threats present a 

significant threat to the Sonoran Desert 

Area bald eagle population. If these 

threats were acting, either 

independently or cumulatively, in such 

a manner as to likely cause a significant 

risk of extinction to the population, we 

would expect to see them expressed in 

terms of the demographic factors that 

we reported in our analysis. In fact, all 

of the rates (e.g., mortality, survival, 

productivity, and occupancy) associated 

with the demographic factors for the 

Sonoran Desert Area population of the 

bald eagle were within the range of 

values observed in other populations of 

the bald eagle in the United States. More 

importantly, simple counts of bald 

eagles breeding in Arizona each year 

indicated that the breeding segment 

increased at an average rate of 4.0 

percent per year from 1987 to 2003 

(Allison et al. 2008, p. 26). Therefore, 

although the threats described above 

vary in their scope and intensity, the 

Service considers the overall threat to 

the Sonoran Desert Area population of 

the bald eagle from these factors to be 

low. 

On the basis of the best scientific and 

commercial data available, we find that 

listing the Sonoran Desert Area 

population of the bald eagle as 

threatened or endangered is not 

warranted. We arrive at this 

determination because, despite the 

presence of these same threats for 

decades, the Sonoran Desert Area 

population of the bald eagle remains 

stable or increasing. In our analysis, we 

have indicated that some of the threats 

are likely to increase in the future. 

However, we do not have any 

information to suggest that these are 

significant threats or threats that could 

cause the Sonoran Desert Area 

population of the bald eagle to be in 

danger of extinction, or likely to become 

so in the foreseeable future. 

We encourage interested parties to 

continue to gather data that will assist 

with the conservation of the species. If 

you wish to provide information 

regarding the bald eagle, you may 

submit your information or materials to 

the Field Supervisor, Arizona Ecological 

Services Office (see ADDRESSES section 

above). The Service continues to 

strongly support the cooperative 

conservation of the Sonoran Desert Area 

bald eagle. 

References Cited 

A complete list of all references cited 

herein is available at http:// 

www.regulations.gov at Docket No. 

FWS–R2–ES–2008–0059, upon request, 

from the Southwest Regional Office of 

the U.S. Fish and Wildlife Service (see 

ADDRESSES section above). 

Author 

The primary authors of this notice are 

the staff of the Southwest Region of the 

U.S. Fish and Wildlife Service. 

Authority 

The authority for this section is 

section 4 of the Endangered Species Act 

of 1973, as amended (16 U.S.C. 1531 et 

seq.). 

Dated: April 17, 2012. 

Daniel M. Ashe, 

Director, Fish and Wildlife Service. 

[FR Doc. 2012–10016 Filed 4–30–12; 8:45 am] 

BILLING CODE 4310–55–P 

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