U.S. Fish & Wildlife Service

Post-delisting Monitoring Plan for the

Bald Eagle (Haliaeetus leucocephalus) in

the Contiguous 48 States
Cover Photo: Bald eagle adult and two chicks. Photo by Brad Tedrick, Illinois Department of

Natural Resources.

 2
U.S. Fish & Wildlife Service

Post-delisting Monitoring Plan for the

Bald Eagle

March 2009

Recommended Citation

U.S. Fish and Wildlife Service. 2009. Post-delisting Monitoring Plan for the Bald Eagle (Haliaeetus

leucocephalus) in the Contiguous 48 States. U.S. Fish and Wildlife Service, Divisions of Endangered Species

and Migratory Birds and State Programs, Midwest Regional Office, Twin Cities, Minnesota. 75 pp.

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Table of Contents 

Acknowledgements ....................................................................................................................... 6

Background ................................................................................................................................... 6

Purpose and Goal.......................................................................................................................... 9

Implementation ............................................................................................................................. 9

Methods........................................................................................................................................ 12

Protocols....................................................................................................................................... 15

Data Quality ................................................................................................................................ 16

Habitat ......................................................................................................................................... 16

Contaminants .............................................................................................................................. 17

Ongoing and Potential Sources of Mortality............................................................................ 18

Response Trigger ........................................................................................................................ 18

Reporting ..................................................................................................................................... 18

References.................................................................................................................................... 20

Appendix 1................................................................................................................................... 22

Tables ........................................................................................................................................... 36

Figures.......................................................................................................................................... 45

Appendix 2................................................................................................................................... 55

Appendix 3................................................................................................................................... 62

Appendix 4................................................................................................................................... 70

Appendix 5................................................................................................................................... 74
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Summary 

The Post-delisting Monitoring Plan (Plan) will monitor the status of the bald eagle by 

collecting data on occupied nests over a 20-year period with sampling events held once 

every 5 years starting in early 2009. The Plan will continue the nest check monitoring 

activities conducted by the States over the past years and add census of area sample plots. 

The area sample plots will be selected from eagle habitat across the contiguous 48 States 

based on known nesting density. The set of known occupied nests (list frame) will be 

combined with the numbers of newly identified occupied nests from the area plot samples 

(area frame) to provide a dual frame estimate (Appendix 1). Statistically combining the 

results of these two data sets will provide a single estimate for the bald eagle population 

of the contiguous 48 States that more closely represents the actual nesting population of 

bald eagles than either the traditional nest check for occupancy or area plot sampling 

alone, based on our pilot studies in Maine, Minnesota, Florida, Washington and Missouri 

(Appendix 1). Reduction in future nest check monitoring (list frame) by the States will 

be compensated by sampling the list frame during the area plot surveys. In addition, dual 

observer sampling protocols are recommended to reduce bias (Appendix 2). Some 

States, particularly those with sparse numbers of nesting pairs, are currently collecting 

data in a highly accurate manner and may not need to employ the dual frame 

methodology. Data from these States will be included as a complete census. 

The Plan recommends that the State agencies continue the occupied nest survey data 

collection and submission and assist with the area surveys while the U.S. Fish and 

Wildlife Service (Service) coordinates the area survey, manages the database, provides 

expertise including dual frame sampling design and data analysis, and initially funds the 

area sampling. This Plan is not intended to replace specific plans to manage eagles or 

monitor them in a different manner for specific management purposes. 

The sample design is based on an 80 percent chance of detecting a 25 percent or greater 

change in occupied bald eagle nests over any period, measured at five-year intervals. We 

believe this is a goal that will both ensure recovery and be cost-effective. Were this 

degree of decline to occur with no further increase, the bald eagle population would still 

be at a level recognized as recovered (from 9,789 occupied nests when the bald eagle was 

delisted in 2007 to 7,342 occupied nests, a 25 percent reduction) based on a population 

estimate of 6,471 when the initial proposal to delist was published in 2000. If such 

declines are detected, the Service’s Bald Eagle Monitoring Team in conjunction with the 

States will investigate causes of these declines, including consideration of natural 

population cycles, weather, productivity, contaminants, other mortality factors, habitat 

changes or any other significant evidence. The result of the investigation will be to 

determine if the population of bald eagles in the contiguous 48 States warrants expanded 

monitoring, additional research, and/or resumption of Federal protection under the 

Endangered Species Act (ESA). At the end of the 20 year monitoring program, we will 

conduct a final review. It is the intention of the Service to work with all our partners 

toward maintaining continued species population expansion and management. 
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Acknowledgements 

This monitoring plan was written by the U.S. Fish and Wildlife Service Bald Eagle 

Monitoring Team: Jody Millar, National Coordinator (Region 3), Suzanne Audet 

(Region 1), Greg Beatty (Region 2), Allan Mueller, Candace Martino, Alfredo Begazo 

(Region 4), Craig Koppie (Region 5), Dan Mulhern (Region 6), Phil Schempf (Region 7), 

and Mary Klee (Region 9); Mark Otto, Migratory Birds program, and John Sauer, US 

Geological Survey-Biological Resources. The States of Maine, Minnesota, Florida, 

Washington, and Missouri provided critical support in participating in the pilot program. 

Background 

Between 1952 and 1957 Charles Broley, an avid eagle watcher, reported that about 80 

percent of the bald eagle (Haliaeetus leucocephalus) nests in Florida he had been 

watching failed to produce any young. By 1958, nesting adult eagles were so scarce in 

his study area that he only found 10 nesting pairs where he had found 47 the previous 

year, and had found 125 nesting pairs 15 years earlier (Carson 1962). This monitoring 

information was ultimately linked to a deadly insecticide in widespread use at that time: 

DDT (Carson 1962). 

Subsequent bald eagle surveys conducted in the 1960s by the National Audubon Society 

and others documented poor nesting success and low numbers of nesting pairs, prompting 

the Secretary of the Interior to publish a Federal Register notice (32 FR 4001) on March 

11, 1967 listing bald eagles south of 40o

 N. latitude as endangered under the Endangered 

Species Preservation Act of 1966 (Pub. L. No. 89-699, 80 Stat. 926). Bald eagles north 

of this line were not included because northern populations were not considered 

endangered at that time. 

In the 1970s, bald eagle surveys conducted by the Service, other cooperating agencies, 

and conservation organizations revealed that the bald eagle population was declining 

throughout the contiguous 48 States. On December 31, 1972, DDT was banned from use 

in the United States by the Environmental Protection Agency. The following year, the 

Endangered Species Act of 1973 (16 U.S.C. 1531-1544) (ESA) was passed. In 1978, the 

bald eagle was listed throughout the contiguous 48 States as endangered except in 

Michigan, Minnesota, Wisconsin, Washington, and Oregon, where it was listed as 

threatened (43 FR 6233, February 14, 1978). 

Listing under the ESA and banning of DDT and other harmful organochlorine chemicals 

resulted in significant increases in the breeding population of bald eagles throughout the 

contiguous 48 States. On February 7, 1990, the Service published an advance notice of a 

proposed rule to reclassify the bald eagle from endangered to threatened in 43 States 

where it was classified endangered and to retain threatened status for the remaining five 

States (55 FR 4209). On July 12, 1994, the Service published the proposed rule for this 

reclassification (59 FR 35584), and the final rule was published on July 12, 1995 (60 FR 
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36000). After reclassification, bald eagles continued to improve to the point where the 

Service believed the species no longer meets the definition of a threatened species. On 

July 6, 1999, the Service published a proposed rule (64 FR 36454) to delist the bald eagle 

in the contiguous 48 States, and requested public comments. The comment period on the 

proposal to delist was reopened on February 16, 2006 (71 FR 8238). The final rule on 

delisting and the Notice of Availability for the draft monitoring plan were published 

simultaneously in the Federal Register (72 FR 37346) on July 9, 2007. That July notice 

opened a public comment period on the draft post-delisting monitoring plan. After the 

comment period closed on October 9, 2007, the Service reviewed each comment received 

and edited the Plan appropriately. 

On March 6, 2008, the U.S. District Court for the District of Arizona ordered bald eagles 

in the Sonoran Desert of central Arizona to again be protected as threatened under the 

ESA, pending further review by the Service. To comply with the court order, on May 1, 

2008, the Service published a final rule in the Federal Register (73 FR 23966) listing the 

potential Sonoran Desert bald eagle distinct population segment in central Arizona as 

threatened. On May 20, 2008, the Service published a Federal Register notice (73 FR 

29096) initiating a status review of bald eagles in the Sonoran Desert area of central 

Arizona and northwestern Mexico. Under the court order, the Service will issue a 12-

month petition finding on whether listing the Sonoran Desert bald eagle under the ESA is 

warranted, and if listing is warranted, then whether those bald eagles should be listed as 

threatened or endangered. For the purposes of this monitoring plan, our approach to 

include these eagles into our population estimate will not be altered by its listing status. 

In the years since Charles Broley’s discovery of declining eagle numbers in Florida, the 

States, Tribes, Service, and our non-governmental partners have engaged in the difficult 

and costly task of monitoring nesting bald eagles. In the ensuing 25 years since listing, 

many States have monitored nesting bald eagles for their entire State annually. With the 

recovery of the bald eagle and removal from the Federal List of Threatened and 

Endangered Species, many States have since reduced their monitoring efforts. 

Post-Delisting Monitoring Requirement of the Endangered Species Act

Post-delisting monitoring is a requirement of the ESA. Section 4(g)(1) requires the 

Service to... 

 

implement a system in cooperation with the States to monitor effectively for not 

less than five years the status of all species which have recovered to the point at 

which the measures provided pursuant to this Act are not longer necessary. 

The Plan described herein exceeds the minimum requirement set forth by the ESA by 

effectively monitoring the status of the bald eagle over a 20-year period using five 

sampling events. 
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History of Plan Development and Pilot Studies

A draft monitoring plan was provided in the proposed rule to delist bald eagles on July 6, 

1999 (64 FR 36454). Slightly more than ten percent of all comments we received on that 

proposal were concerned with post-delisting monitoring and the draft monitoring plan. 

Since then, the monitoring plan has been revised in such a way that it is responsive to the 

comments we received. 

In September 2000, a bald eagle monitoring workshop was held at the Service’s Patuxent 

Wildlife Research Center in Maryland, attended primarily by State biologists involved 

with bald eagle monitoring. As a result of that workshop, the Service in cooperation with 

the U.S. Geological Survey’s Biological Resources Division (USGS-BRD), proposed a 

pilot study. The pilot study, funded by the USGS for 2004 and 2005, incorporated 

methods traditionally used by some States to monitor occupied bald eagle nests while 

adding an area sample plot census. 

The first pilot study was conducted in cooperation with the Maine Department of Inland 

Fisheries and Wildlife in spring 2004. In addition to Maine’s yearly aerial survey of bald 

eagle nests (list survey), forty-one 10 kilometer (km) x 10 km area plots were surveyed 

from the air (area survey) using a dual observer method. Estimates from the area survey, 

from Maine’s list of bald eagle occupied nests, and a combination of those data were 

compared and analyzed. Those results were presented at a second workshop held at the 

Patuxent Wildlife Research Center in October 2004. The purpose of this workshop was 

to review results from the first pilot study and to discuss approaches and possible changes 

for a broader pilot study to be conducted in winter/spring 2005. Biologists from State 

natural resource agencies were invited to this workshop, but emphasis was placed on 

representatives from the States proposed for pilot studies in 2005: Florida, Minnesota, 

and Washington. 

As a result of that workshop, a second pilot study was implemented in three States 

(Florida, Minnesota, and Washington) during the 2005 nesting season. The 2004 and the 

2005 pilot studies detected 18 to 40 percent more occupied nests with greater precision 

using the dual frame approach than calculated for either area or list frame sampling alone 

(Appendix 1, p.22). Thus, the dual frame approach to sampling was selected as superior 

for the bald eagle post-delisting monitoring plan. 

To implement this monitoring plan, we propose to cooperate with and provide technical 

assistance to our State, Tribal, Federal, and non-governmental partners in all aspects of 

planning and implementing a dual frame approach to bald eagle monitoring. This plan 

does not monitor causal factors such as habitat modification or disturbance as defined 

under the Bald and Golden Eagle Protection Act. For additional information on 

protections for bald eagles under the Bald and Golden Eagle Protection Act (BGEPA), 

please refer to the Service's National Bald Eagle Management Guidelines (72 FR 31156) 

and regulatory definition of the term "disturb" (72 FR 31132) that were published in the 

Federal Register on June 5, 2007. Existing take authorizations for bald eagles issued 
9

under the ESA became covered under the BEGPA via a final rule published in the 

Federal Register on May 20, 2008 (73 FR 29075). 

Additionally, this Plan does not replace specific plans to monitor bald eagles more 

regularly or in a different manner for specific management purposes. We encourage 

partners with existing plans that meet or exceed this Plan's monitoring standards to work 

with us to continue using their own monitoring and conservation efforts, especially where 

continuation of those plans will ensure consistency and comparability with existing data 

sets. 

Purpose and Goal 

The purpose of post-delisting monitoring is to determine if at any time the population of 

bald eagles in the contiguous 48 States warrants expanded monitoring, additional 

research, and/or resumption of Federal protection under the ESA. The population of bald 

eagles in the contiguous 48 States will be estimated by monitoring changes in the number 

of occupied bald eagle nests in the contiguous 48 States. The goal of the bald eagle postdelisting monitoring plan is to detect a 25 percent or greater change in occupied bald 

eagle nests over any period, measured at five-year intervals based on an 80 percent 

chance of detecting such a change. We believe this is a goal that both ensures recovery 

and is cost-effective. If a 25 percent decline is measured, it means a reduction to a level 

still recognized as recovered (from 9,789 occupied nests in 2007 to 7,342 occupied nests, 

a 25 percent reduction) based on a population estimate of 6,471 when the initial proposal 

to delist was published in 2000, and assuming no further population increase preceding 

the decline. If such declines are detected, the Service in conjunction with the States will 

investigate causes of those declines. At the end of the 20-year monitoring program, we 

will coordinate with States and our other partners to conduct a final review and provide 

recommendations to insure a properly managed population of the recovered bald eagle. 

Implementation 

Bald eagle monitoring will require a well coordinated national effort, involving the 

States, Tribes, Federal agencies, and other cooperators. The following describes the roles 

and responsibilities of the parties involved in bald eagle monitoring under this Plan.

Service Bald Eagle Monitoring Team

The Service’s national bald eagle monitoring team (Team) comprised of a national 

coordinator, regional coordinators from each of the Service’s seven Regions, and a 

biometrician (a biological statistician) has been formed to develop and implement the 

Plan. The Midwest Region of the Service is the lead Region for this effort (Appendix 4). 

This Team will work closely with the States and all other interested parties, particularly 

during each 5th-year monitoring effort, to ensure that Plan implementation is wellcoordinated and efficient. States will be directly involved in collecting, reviewing, and 

analyzing survey data, as well as identifying significant issues and developing 

recommendations to address these issues. 
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The role of the Service’s national coordinator is to coordinate within the Service and with 

States, Tribes, other Federal agencies, and non-governmental organizations. Together 

with the Team members, the coordinator recommended draft and final Plans to the 

Service’s Directorate. The Team will communicate with State resource agencies and 

cooperators; coordinate the planning, implementation, and analysis of the surveys and 

summarize the monitoring results in cooperation with States and other cooperators; and 

prepare interim and final reports on the monitoring results. The team is tasked with 

making recommendations based on survey results, seeking partnerships to implement the 

Plan, advocating for resources to carry out the monitoring program, and developing 

partnerships for any needed studies. 

 

The role of the Service biometrician is to develop and maintain a national database on the 

States’ known bald eagle nest list data (spatial and non-spatial); design the surveys based 

on State boundaries and Bird Conservation Regions as a means of stratifying high, low, 

and trace nesting density; coordinate and maintain a national database of the survey data 

from the various States; and conduct the data analysis, interpretation, and summary for 

the national surveys. 

The Service will fund the area frame surveys for the initial baseline survey in 2009, 

including the use of aircraft and pilots from the Service’s Migratory Birds program to 

complete the surveys. We will continue to work with the States, Tribes, and our other 

partners to secure funding for future surveys. 

Coordination with States

Section 4(g)(1) of the ESA states that “The Secretary shall implement a system in 

cooperation with the States (emphasis added) to monitor effectively for not less than five 

years the status of all species which have recovered to the point at which the measures 

provided pursuant to this Act are no longer necessary...” The Service worked with the 

States to develop this Plan. 

As described in the Background, this Plan is the product of comments from the initial 

proposal to delist the bald eagle, two workshops, and two seasons of pilot studies 

involving four States. This Plan was framed based on the results of those efforts. Early 

in the Plan development process, Service Team members contacted the States within their 

respective regions to determine a coordinator for each State with whom we could 

coordinate our efforts. States were asked to summarize their bald eagle monitoring 

protocol and to provide their most recent survey data. The Service Team also solicited 

suggestions regarding Plan content, methods, and format from the State biologists. Once 

a draft plan was developed, the Non-game Technical Committees of the Pacific, Central, 

Mississippi, and Atlantic Flyway Councils were asked to provide peer review. The Nongame Technical Committees of the various flyway councils are composed primarily of 

State biologists. Service Team members presented updates and answered questions on 

the draft Bald Eagle Post-delisting Monitoring Plan at the flyway councils’ biannual 
11

meeting in March 2007. States were formally requested to provide review and comments 

during the public review period. In addition to the technical committee peer review 

comments from the flyway councils, 12 States provided comments on the draft Plan. 

The Team’s national and regional coordinators will work closely with the State 

coordinators and other cooperators to provide technical assistance on implementing the 

Plan and submitting the data after each monitoring period. In coordination with the 

States, the Service will propose adjustments to the sampling design, if necessary. This 

effort will also require the Service biometrician to work closely with the State 

coordinators and the Team to select sample areas and maximize sampling efficiency. For 

those years that fall between the monitoring years outlined in this Plan, the Service will 

have an ongoing request for occupied nest monitoring data that can be entered into a 

secure, web-based database (Appendix 3). Data on productivity and any information 

regarding major habitat changes, contaminants, or mortality events collected by States or 

other partners may also be submitted to the Team at any time. 

For the baseline monitoring/first year of sampling in 2009, the States will be asked to: 

 Update their nest lists and enter this data on the secure web site. 

 Provide experienced bald eagle observers for the aerial part of the survey and 

participate in training; 

 Provide input on refining stratum boundaries, definitions of bald eagle habitat 

specific to the State, and identification of breeding season dates; and 

 Reconcile list nests found in the area samples and enter that data into the 

secure web site. 

Coordination with Tribes

The Service values the cooperation and participation of the Tribes in our bald eagle 

recovery efforts, including post-delisting monitoring. Bald eagles are important to the 

Tribes for cultural, religious, and ceremonial purposes, giving the Tribes a vested interest 

in the continued conservation of the species. While the geographic boundaries of the 

States will be the basis of the national monitoring effort, information on nest occupancy 

on tribal lands has been and will continue to be important information. We encourage the 

Tribes to maintain updated lists of nests on their lands and share that information with the 

States and the Service. Prior to initiation of the nest surveys, the Service will coordinate 

with Tribes regarding any randomly selected area plots that may fall on tribal lands. 

Coordination with Other Partners

Bald eagle monitoring in most States has been carried out by a combination of Federal 

agencies, Tribes, private organizations, and individuals. While the Service, in 

cooperation with the States, is responsible for post-delisting monitoring of bald eagles, 

continued participation and cooperation of all our partners is important for monitoring 

success. We anticipate that the combined efforts of all of our partners working together 

will provide the necessary resources to implement this Plan. 
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Other Monitoring Efforts 

While the dual frame methodology is the formal strategy being recommended to monitor 

the breeding population of bald eagles, there are other local and national efforts that will 

continue to assist in evaluating the status of the bald eagle population. Many States have 

annual flight surveys to count nesting bald eagles. Some States will conduct a second 

flight to assess productivity. Wintering bald eagle surveys have been conducted since 

1979 and the National Bald Eagle Winter Survey has become institutionalized in many 

States across the country (Steenhof et al. 2002). This effort provides an opportunity to 

identify and manage for important eagle wintering areas, and provides information on 

wintering distribution, abundance, and age class. Biologists at important bird migration 

points have been tracking migrating bald eagles for many years. Service National 

Wildlife Refuges and other land managers track productivity as well as nesting and 

migrating bald eagles. Continuing these efforts post-delisting and providing that 

information to the Team members will improve our ability to evaluate the status of the 

bald eagle. 

Methods 

Sampling Design: The Dual Frame Method 

These methods are described in more detail in Appendix 1, Contiguous 48 States Bald 

Eagle Breeding Pair Survey Design. A generalized description of the methodology 

follows. 

The Service will work with States, Tribes, Federal agencies, and other partners to conduct 

a survey of occupied bald eagle nests that incorporates information from two sampling 

strategies. The first strategy uses the list of all currently known occupied bald eagle nest 

locations. This is called the list frame and is the method employed for the last 25 to 30 

years by the States. The second strategy uses aerial surveys to count occupied bald eagle 

nest locations from randomly selected plots. This is called the area frame (Haines and 

Pollock 1998). A frame is a set of all possible elements from which we can sample. Data 

gathered in these two sampling frames allows aggregation of numbers from occupied 

nests found in the list and occupied nests found in the area frames, resulting in an 

estimate of the total number of occupied nests that is more accurate than the use of either 

frame alone based on results from the pilot studies (Appendix 1). 

 List Frame 

The list frame for this Plan is a summary of all currently known occupied bald eagle nests 

for the contiguous 48 States. This includes the current State occupied nest lists and will 

include all future updates to those lists. The list will be updated by States and partners 

conducting bald eagle nesting surveys in the manner that those surveys were conducted 

while the bald eagle was still listed under the ESA. Each State will enter updates to the 

list into a secure, web-based database. The updates will include confirmation of activity 
13

at known nest sites and the addition of new occupied nests found either through the nest 

surveys, or by nest locations found during the area frame survey that were previously 

unknown. Historically, States conduct bald eagle nest surveys at varying levels of effort 

and at varying time intervals. Thus, the list frame will be composed of data collected in 

different years and of varying intensity. Should confidence in the list frame erode over 

time due to reduced survey effort, the list may need to be sampled concurrent with the 

area frame to provide an estimate of nests that are in the list frame. 

 Area Frame 

The area frame is composed of randomly selected plots within which bald eagle habitat is 

carefully surveyed for all occupied bald eagle nests. The plots are 10 km x 10 km each 

(or equivalent area), selected from a grid matrix that has been overlaid on a habitat 

stratum. The strata are used to increase sampling efficiency, and are based on State 

boundaries and Bird Conservation Regions (BCRs). The BCRs group regions with 

similar environmental features (Sauer et al. 2003). To accommodate State-specific needs, 

we divided BCRs into States, and use these State-BCR units as our initial strata 

(Appendix 1, Figure 1). The State-BCR strata are further divided into High, Low, and 

Trace categories based on bald eagle habitat quality and nesting density (Appendix 1, 

Figure 2). Appendix 2 outlines the protocol for collecting area frame data for this Plan. 

Observations of nest occupancy collected in this area-based sample will contain both new 

nests and nests that also occur in the list frame. 

Dual Frame 

The dual frame method of analysis combines sample information from both the list frame 

and the area frame to arrive at a more precise estimate of occupied nest density across the 

entire study area (Haines and Pollock 1998). To conduct the analysis, occupied nests 

identified in the area frame sampling are separated into the two categories: the overlap 

(nests in the plots that also occur in the list) and nonoverlap (nests that are newly found in 

the plots). The nonoverlap nests are identified, and are used to estimate the total number 

of nests not in the list. The sum of the estimates from the area frame and the list frame 

are used to determine a total number of occupied eagle nests within the study area. 

Monitoring Study Area

The goal of this Plan is to detect changes in the number of occupied bald eagle nests in 

the contiguous 48 States. The study area is the entire contiguous 48 States because one 

population was identified as the listed entity at the time of removal from the Federal List 

of Threatened and Endangered Species. Sampling at this scale will be more costeffective than sampling at a regional or smaller scale. 

A GIS-based map has been developed depicting bald eagle nesting density in the 

contiguous 48 States (see Appendix 1, Figure 3), which is the study area. The map is 

based on the most recent nesting data collected at different times in different ways from 

each State and compiled into one list for the contiguous 48 States (list frame). 
14

Frequency and Duration of Sampling

If we used a narrow interpretation of the ESA’s requirement for monitoring a minimum 

of five years after delisting, this would result in monitoring for one breeding cycle. The 

bald eagle’s distinctive white head and tail are not fully visible until four to five years of 

age when eagles are considered to have reached sexual maturity. In some areas of the 

country, birds in sub-adult plumage have been known to form pair bonds, defend 

territories, and construct nests. In other regions with dense populations and competition 

for nest sites, eagles may not breed until six or seven years old (Buehler 2000). Thus, 

though the exact breeding cycle varies, the majority of bald eagles reach maturity at 5.5 

years of age (Buehler 2000). In order to assess several generations of bald eagles after 

delisting, this Plan recommends monitoring bald eagle nesting populations at five-year 

intervals (which would follow the development cycle to maturity for one generation), for 

four generations or a total of 20 years. 

Many States monitor bald eagle nests on an annual basis because the surveys provide 

valuable resource data. Comments we have received from a number of States, however, 

indicates that their future bald eagle monitoring will be greatly reduced due to its 

recovery and the need to allocate funding to other areas. Thus, five-year survey intervals 

will provide more data for states where surveys are not otherwise planned. It may also 

provide a cost savings for other States if they can use these data at five-year intervals to 

satisfy their needs. 

Sampling the List Frame 

The Plan recommends States maintain their lists of known nest sites. It is expected that 

this will be done with varying degrees of effort. Ideally, the number of occupied nests in 

the list would be determined through a periodic census of all nests on the list. In States 

where lists are not maintained, known nest sites can be sampled as part of the area 

survey. 

Sampling the Area Frame 

The area frame must be sampled to obtain unbiased estimates of the total number of 

occupied nests. To do this, the Service’s biometrician will determine area frame plot 

numbers for each stratum in coordination with the States. Some plots initially selected 

for the area sample may have characteristics that make them unreasonable to sample. For 

example, the plot may be too far from an airport to be cost effective or allow for safe 

reserves of fuel. Plots near urban areas could contain too many obstructions such as 

transmission lines or cell towers to permit safe survey conditions. Therefore, we will 

initially select an additional 10 percent of plots to sample to ensure alternate plots are 

available if different plots are necessary. For example, if 10 plots will be sufficient to 

meet the stated goals for precision and accuracy, we will plan to sample 11 plots, 

assuming that logistical or safety issues may preclude sampling at one plot. Should all 
15

plots be feasible, sampling will cease when the minimum number of plots first selected 

has been sampled. 

Protocols 

The area frames will be sampled using protocols consistent with those developed during 

the pilot studies. A detailed discussion of standard operating procedures is included as 

Appendix 2. A double observer protocol will be implemented for the area frame 

sampling whenever possible to estimate the proportion of nests missed during that area 

sampling event (Nichols et al. 2000). Protocols for double observer sampling are also 

presented in Appendix 2. Aircraft observers should be familiar with the terrain and 

nesting habitats of eagles in their area. The front seat observer should be the primary 

data recorder. All occupied nests and the number of visible young should be recorded. 

The aircraft should be flown at 200 to 700 feet above ground level (agl) at about 100 mph 

or 87 knots. Only the parts of plots that are composed of potential eagle habitat will be 

flown. Flight paths will be defined on maps prior to conducting the surveys. We note 

that protocols for assessing occupancy status of a nest may differ regionally, and timing 

of surveys will also differ regionally. Consequently, protocols for sampling must be 

reviewed regionally for consistency as part of survey implementation. 

Reproductive Terminology 

Standard terminology for describing the status of bald eagle nests and territories is 

essential, especially if a meaningful comparison is to be made of the data collected by 

different workers over many years and throughout the nation. The following definitions 

are derived from Postapulsky (1974), Fraser (1978), Steenhof and Kochert (1982), and 

Steenhof (1987). They are entirely separate from, and should not be substituted for, 

definitions in other bald eagle documents developed by the Service. 

 

Active nest (breeding): A nest where eggs have been laid. Activity patterns are 

diagnostic of breeding eagles (or those with an “active” nest). This category excludes 

non-nesting territorial pairs or eagles that may go through the early motions of nest 

building and mating, but without laying eggs. From egg-laying to hatching, incubation 

typically lasts 35 days (Stalmaster 1987). 

Alternate nest: One of several nest structures within a breeding area of one pair of eagles. 

Alternate nests may be found on adjacent trees, snags, man-made towers, or on the same 

or adjacent cliffs. Depending on the size of the breeding territory, some alternate nests 

can be up to a few miles away. 

Bald eagle nesting habitat: For this study, bald eagle nesting habitat will need to be 

defined for each region to assure sampling efficiency. In general, bald eagle nesting 

habitat will include a description of typical nesting structure for the region and proximity 

to a food source, usually a larger sized water body. The pilot States generally defined 

bald eagle nesting habitat as supercanopy or sturdy-structured trees within one mile of 

water bodies greater than 35 acres and rivers greater than 330 feet in width and all coastal 
16

waters with suitable nesting substructures nearby. However, local or regional habitat 

parameters will have to be modified with input from local biologists to fit local 

conditions, including in much of the arid Southwest. 

Breeding area (nesting/breeding territories): An area that contains or that was 

previously known to contain one or more nests within the territorial range of a mated pair 

of eagles. 

Nest: A structure, composed largely of sticks, built by bald eagles for breeding. 

Unoccupied breeding area/territory/nest: A nest or group of alternate nests at which 

none of the activity patterns diagnostic of an occupied nest were observed in a given 

breeding season. Breeding areas must be previously determined to be occupied before 

they can be recognized and classified as unoccupied. 

Occupied nest: Any nest where at least one of the following activity patterns was 

observed during the breeding season: 

 a recently repaired nest with fresh sticks or fresh boughs on top; 

 one adult sitting low in the nest, apparently incubating; 

 one or two adults present on or near the nest; 

 one adult and one bird in immature plumage at or near a nest, if mating behavior 

(display flights, nest repair, coition) was observed; 

 eggs were laid (detection of eggs or eggshell fragments); 

 any field sign that indicate eggs were laid or nestlings hatched; or 

 young were raised 

The total number of occupied nests is the index of abundance for this survey. Efforts will 

be made to survey during the period when adults are most likely to be incubating and the 

identification of occupancy is most often confirmed with the presence of one or more 

adults. Observers will make note of nests that are found but where bald eagles are not 

present. Distinctions between repaired and not repaired empty nests will be made in 

addition to any uncertainties such as questioning whether the empty nest is that of an 

osprey. In case of doubt, the default determination will be negative. 

Data Quality 

The survey data sets used in the Bald Eagle Post-delisting Monitoring Plan will adhere to 

the Service’s data quality standards in naming variables and in choosing values those 

variables can take (www.fws.gov/stand). The metadata for our spatial data will be 

written according to the Federal Government Data Committee standards 

http://www.fgdc.gov/metadata/geospatial-metadata-standards. 

Habitat 

The Service will not monitor changes in bald eagle habitat directly. However, the Team, 

in conjunction with the States and other partners, will accept and review data indicating 
17

significant changes in bald eagle habitat in the contiguous 48 States. Should a 25 percent 

decline in the bald eagle population occur, the Service will consider habitat data when 

determining potential causal factors for the decline. 

 

Contaminants 

The Service worked with the USGS-BRD to develop a searchable database/library 

dedicated to contaminants investigations of bald eagle, osprey (Pandion haliaetus), and 

peregrine falcons (Falco peregrinus). The objective was to create a readily available 

source of information to consider should the bald eagle (or peregrine) population decline. 

Osprey contaminants data are relevant to bald eagles as they occupy a similar niche. 

The USGS identified, acquired, and assigned keywords for published and unpublished 

literature about contaminants in bald eagles, osprey, and peregrine falcons. The USGS’s 

Richard R. Olendorff Memorial Library in Boise, Idaho currently maintains several 

hundred references relevant to this topic as part of the Raptor Information System. New 

and existing references were assigned contaminant-related keywords, established by the 

Service’s contaminants biologists. These keywords are listed on the contaminants 

database page at the following website: http://ris.wr.usgs.gov/Contaminants.asp .

Citations for all new references were incorporated into the existing Raptor Information 

System database and are served from the existing website (http://ris.wr.usgs.gov/). Many 

of the citations include links to the full text of articles that are being served on the World 

Wide Web. We will also seek resources from the National Biological Information 

Infrastructure (NBII) to serve the PDF files and abstracts as well as the citations from a 

separate web site. Keeping this database relevant will require periodic updating. A 

Service environmental contaminants biologist will coordinate this effort (see Appendix 4, 

Region 5 contacts). 

References from the contaminants database can be retrieved by entering the first keyword 

in the keyword search box using the autocomplete function. Enter additional keywords 

from the keyword popup list, then type in FWSEC as the final keyword in the keyword 

box. Not entering FWSEC will bring up references about other species as well as 

abstracts and popular articles about the subject species. 

By creating this database, biologists in the position of recommending regulatory actions 

based on post-delisting monitoring trends will have a clear overview of the most recent 

findings of contaminant effects on these three species. Deleterious effects resulting from 

contaminant exposure was a major reason the bald eagle and peregrine falcon were listed 

under the ESA. Data demonstrating reduction in contaminant exposure supported the 

proposal to delist the bald eagle and peregrine falcon. Should additional studies be 

needed during post-delisting monitoring, the database will clarify what has been studied 

and what has not. 
18

Ongoing and Potential Sources of Mortality 

In species with a long life span and a relatively low reproductive rate like the bald eagle, 

adult mortality can be a very important factor in determining the stability of a population 

(Stalmaster 1987). Bald eagles (and many other raptors) are killed as a result of trauma 

from collisions with power lines, vehicles, and other obstacles; electrocution; disease; 

poisoning; shooting; and other factors. 

As part of the Plan, bald eagle mortality will be tracked to alert the Team to new and 

potentially significant sources of mortality. We will request information on bald eagle 

deaths from sources that are known to encounter dead eagles most frequently: State 

wildlife conservation agencies; Service law enforcement officers; wildlife rehabilitators; 

the National Wildlife Health Center in Madison, Wisconsin; and the National Fish and 

Wildlife Forensic Laboratory in Ashland, Oregon. If an unusually large number of 

mortalities occur, the Service and its partners will consider the information in regards to 

specific causes and/or locations for investigation of patterns and possible corrective 

action, if necessary. 

Response Trigger 

The Service has established the following Plan goal as the response trigger for additional 

investigation: 

A 25 percent or greater decline in occupied bald eagle nests between any two periods 

measured at 5-year intervals detected with a power of 80 percent and an error rate of 

10 percent. 

If such declines are detected, the Service’s Bald Eagle Monitoring Team will coordinate 

with the States to investigate causes of these declines, including consideration of natural 

population cycles, weather, productivity, contaminants, mortality factors, habitat changes, 

data from other monitoring efforts, or any other significant evidence. At the end of the 

20-year monitoring program, we will coordinate with States and our partners to conduct a 

final review and provide recommendations to insure a properly managed bald eagle 

population. Any relisting decision by the Service will be made by evaluating the status of 

the bald eagle relative to the ESA’s five listing factors (ESA § 4(a)(1)). 

 

Reporting 

The Service will issue a report detailing the results of the first breeding population 

survey, which will serve as our baseline for future comparison. This report will be 

available to the public in printed form and on the internet at 

http://www.fws.gov/migratorybirds/BaldEagle.htm within one year of survey completion. 

The report will include a description of the geographic areas surveyed, the survey 
19

protocol, and an estimate of the breeding population of bald eagles in the contiguous 48 

States. 

Every five years, the Service intends to issue a report following completion of the 

updated continental breeding population sampling. This report will contain information 

similar to the baseline report, including an updated breeding population estimate and 

comparison with previous data, and will be available to the public. Reports will also 

suggest ways to improve sampling protocols or other aspects of the Plan design, if 

necessary, and will provide updates to the Plan. 

Each report will include comments on the need for any investigative action and the 

relationship between the survey results and the response trigger. This Plan is designed to 

detect substantial declines in occupied nests with reasonable certainty and precision. If 

the response trigger is met or exceeded, the Service will consult with the States and other 

partners and make recommendations for future actions. If necessary, an evaluation of the 

threats to bald eagles will be made using the five factors required under the ESA to list a 

species on the Federal List of Threatened and Endangered Species. 

The Service intends to also provide a summary report on bald eagle mortality every five 

years. Bald eagle mortality reports will describe the number and causes of reported eagle 

deaths during the five-year period, cumulative deaths reported since the completion of 

baseline monitoring, and the geographic distribution of the reported deaths. Emphasis 

will be on concentrations of multiple deaths. In this way, specific causes and/or locations 

of high eagle mortality may be identified for investigation of patterns and possible 

corrective action, if necessary. 

At the end of the 20-year monitoring period, the Service will review all available 

information to determine if continuation of monitoring is appropriate. The decision to 

continue or end the monitoring program will be explained in the final monitoring report, 

which will be made available to the public as described above. 
20

References 

Buehler, D.A. 2000. Bald eagle Haliaeetus leucocephalus. No. 506. In A. Poole and F. 

 Gill [eds.]. The Birds of North America. The Birds of North America, 

 Inc., Philadelphia, Pennsylvania. 40 pp. 

Carson, R.L. 1962. Silent spring. Houghton Mifflin Co., New York, New York. 368 

pp. 

Fraser, J.D. 1978. Bald eagle reproductive surveys: accuracy, precision, and timing. M.S. 

Thesis, Univ. Minnesota. St. Paul, Minnesota. 82 pp. 

Grier, J.W. and J. E. Guinn. 2003. Bald eagle habitats and responses to human 

disturbance in Minnesota: Final report. Unpublished report. Final report to the 

Minnesota Department of Natural Resources, Natural Heritage and Nongame Wildlife 

Program, Division of Ecological Sciences. St. Paul, Minnesota. 44 pp. 

http://files.dnr.state.mn.us/eco/nongame/projects/consgrant_reports/2003/2003_grier_

guinn.pdf. 

Haines, D.E. and K.H. Pollock. 1998. Estimating the number of active and successful 

bald eagle nests: an application of the dual frame method. Environmental and 

Ecological Statistics 5, 245-256. 

Nichols, J. D. J. E. Hines, J. R. Sauer, F. W. Fallon, J. E. Fallon, and H. J. Heglund. 

2000. A double-observer approach for estimating detection probability and 

abundance from point counts. Auk 117(2):393–408. 

Postapulsky, S. 1974. Raptor reproductive success: some problems with methods, 

criteria, and terminology. Pages 21-31 in F.N. Hammerstrom, Jr., B.E. Harrell, 

and R.R. Olendorff, eds. Management of raptors. Raptor Res. Found., Vermillion, 

S.D. 

Sauer J.R., J.E. Fallon, and R. Johnson. 2003. Use of North American Breeding Bird 

Survey data to estimate population change for bird conservation regions. Journal 

of Wildlife Management. 67:372–389. 

Stalmaster, M.V. 1987. The bald eagle. Universe Books. New York, New York. 

Steenhof, K.L. and M.N Kochert. 1982. An evaluation of methods used to assess raptor 

nesting success. Journal of Wildlife Management. 46: 885-893 

Steenhof, K. L. 1987. Assessing raptor reproductive success and productivity. Pages 

157-170 in B.G. Pendleton, B.A. Milsap, K.W. Cline, D.M. Bird eds. Raptor 

Techniques Manual. National Wildlife Federation, Institute for Wildlife Research, 

Scientific and Technical Series. No. 10, Washington, D.C. 
21

Steenhof, K., L. Bond, K. Bates, and L. Leppert. 2002. Trends in Mid-Winter Counts of 

Bald Eagles Across the Contiguous United States, 1986-2000. Bird Populations 

6:21-32. 
22

Appendix 1 

Contiguous 48 States Bald Eagle Breeding Pair Survey Design 

by Mark C. Otto and John R. Sauer 

Introduction

Bald eagle biologists have focused on site-specific monitoring of eagle nest sites both to 

monitor population change and to catalog areas for management of the species (Bartish 

1994). These site-specific efforts form a critical resource for eagle monitoring, and the 

Plan seeks to maintain these lists of eagle nest sites and to assess their occupancy status. 

However, particularly in areas where eagles are increasing, sampling these lists is not an 

adequate monitoring program, as many possibly occupied nests exist that are not in the 

lists. Consequently, while the delisting criteria are based on the existing lists, and they 

form a critical component of the monitoring program, additional sampling is 

recommended in conjunction with the list sampling to obtain unbiased estimates of 

occupied eagle nests. This dual-frame approach provides estimates of occupied eagle 

nest abundances that are not limited to the list of nests, and provides a flexible strategy 

for estimating abundance that is not limited to regions where the lists are maintained. 

Pilot studies were conducted to assess the feasibility of the dual-frame sampling design. 

Generally, eagle pairs choose one nest of a possible number of nests in their territories to 

occupy and use for brood-rearing in a given season. Many States collect information on 

territories along with information on the nests. Because information on territories is not 

collected consistently across all States and because we cannot assign territories to new 

nests found on the area survey, we use occupied nests as our sampling unit. We assume 

that determining the number of occupied nests is equivalent to determining number of 

territories. This imposes a dependence among local nests in occupancy, as only a single 

nest in a territory will be occupied. Practically, this lack of independence does not affect 

the estimation when we sample nests instead of territories. 

Geographic information about suitable bald eagle breeding habitat and existing nests can 

be used to develop an efficient sample design for the species. We recommend that the 

sample design: (1) stratify by regions (physiographic strata within States) to permit more 

intensive samples in regions with a higher density of bald eagle nests; (2) use a dualframe design to sample known nest sites but also conduct an area-based sample to 

estimate the total number of nests; (3) use habitat information within regions to further 

focus sampling efforts; and (4) account for nests not observed by estimating detection 

probabilities using double observer survey methods (Thompson 2004). 

Dual-frame sampling uses a sample from the list of known nests, in combination with 

additional sampling, to estimate the total number of occupied nests. For the additional 

sampling, the study area is divided into plots, and a sample of these plots is randomly 

selected and censused for occupied eagle nests. This set of plots is known as a sample 

frame, and the selected plots are a random sample from this frame. In accordance with 
23

statistical sampling theory (Lohr 1999), results from the sample plots allow us to 

calculate an estimate for the entire study area. The additional information from the 

sample from the list of nests, however, can be incorporated into the estimation. If nests 

that are on the list but are also known to be in the sample plots are identified and removed 

from the sample (a process known as unduplication), the remaining occupied nests 

observed in the plots can be used to estimate the total number of occupied nests not in the 

list. The occupied nests in the list and the occupied nests seen only on the plots can be 

added to provide an estimate of the total number of occupied nests. 

Additional effort is required during the area surveys to ensure that we account for 

occupied nests that are in the sampled area but are not seen during sampling. Use of a 

protocol involving two independent observers (double-observer sampling, Nichols et al. 

2000) permits estimation of the number of nests that are not observed. For more details 

on the double-observer survey method, refer to Appendix 2. 

To assess the feasibility of using a dual-frame sample design for bald eagle post-delisting 

monitoring, the Biological Resources Division of the U.S. Geological Survey (USGS) 

and the Service conducted pilot surveys over three years (2004–2006) in five States 

(Maine, Florida, Minnesota, Washington, and Missouri). Based on the results of these 

pilot studies, the overall sampling approach described here was developed. The pilot data 

were also used to predict the effort needed in a national delisting monitoring program. 

In this appendix, we discuss the pilot study results, the national design, and the effects of 

list coverage of the nest list on the cost-variance functions. The proposed design expands 

on the approach used in the pilot surveys to a national monitoring program for bald 

eagles. The discussion includes: (1) stratification and how it can be simplified; (2) list 

frame (all known nests from State nest lists in the contiguous 48 States) and how they can 

be clustered within plots to reduce flying time; (3) area frame (all 10 km x 10 km plots 

covering the contiguous 48 States); and (4) estimation of detection probability using 

double observer techniques with the area survey. 

Pilot Studies

Pilot studies were conducted in Maine in 2004, and Florida, Minnesota, and Washington 

in 2005. Additionally, biologists in Missouri volunteered to test the methods in 2006. 

The pilot studies were designed to test the effectiveness of the Haines and Pollock (1998) 

dual-frame design in a variety of geographic areas. The States involved in the pilot 

studies differed both in eagle abundance and in the completeness of their list frames, 

providing a variety of situations for evaluating the dual-frame approach. The eagle nest 

surveys for the pilot studies were collaborations among USGS, Service, and State 

biologists experienced in bald eagle surveys. The State biologists were consulted on 

design issues, conducted surveys of their list frames, and were observers for the area 

frame components of the surveys. 

For the list frame, State biologists censused or sampled the known nests from the ground, 

helicopter, or plane as had been done in previous surveys. The number of occupied nests 
24

was determined from the product of the number of nests in the list frame and the 

proportion of occupied nests estimated during the survey. If the list was censused (all 

nests checked), the variance was zero; if the list was sampled, the variances were 

determined according to the methods described by Thompson (1992, p. 35). 

To implement the dual-frame protocol, an aerial survey of 10 km x 10 km plots was 

conducted over the same strata as the list frame survey. To select plots: (1) each State 

was divided into a grid of 10 km x 10 km plots; (2) the plots were assigned to strata based 

on the predominant habitat type in each plot; (3) nest densities and their standard 

deviations for each stratum were obtained from the previous list frame; and (4) optimal 

allocations for the area frame were determined according to survey sample design theory 

(Lohr 1999, p. 104). Consequently, higher density, more variable, and less costly strata 

were sampled more intensively. Random samples of plots were drawn in proportion to 

the optimal allocation in (4). 

All eagle habitat (as defined by the State biologists) in each sample plot was examined 

during the aerial survey. A double-observer protocol was developed and implemented to 

estimate the number of nests missed during the survey. Observers in the front and rear 

right side seats of the aircraft made independent observations of bald eagles and eagle 

nests. The observations were reconciled immediately after the aircraft had passed the 

nest. The “capture history” (i.e. seen-seen, seen-not seen, etc.) of each observation was 

recorded (see Appendix 2, Standard Operating Procedures). Detection probabilities for 

individual observers and both observers together were obtained using the software 

program DOBSERV (Nichols et al. 2000, http://www.mbr-pwrc.usgs.gov/software.html). 

Including observer detection in the sample allocation specifies that lower detection 

probability and more variable detection probability strata should be sampled more 

intensively. 

The dual-frame estimate was obtained from combining the list frame with the area frame 

surveys by unduplication. Unduplication removes all the nest observations that were on 

both the list and the area frames and leaves only the number of new nests. After the 

unduplication, list and area estimates become independent from each other because they 

have no common observations. The list and area totals can then be added to estimate the 

total number of nests. List and area variances can also be summed to estimate a total 

variance. 

Pilot Study Results 

Results indicate that the dual-frame approach with detectability estimation is useful in 

providing both (1) an estimate of the number of occupied nests that are not included in 

the list of nests and (2) an estimate of the detection rate of nests when sampling plots. 

The variances of the dual-frame estimates were smaller than both the mean squared error 

of the list total and the sample variance of the area survey. Dual-frame estimates of the 

total number of nests were 421 in Maine in 2004, 1,481 in Florida (using the 2003 nest 

list), 1,327 in Minnesota and 1,939 in Washington in 2005, and 123 for Missouri in 2006. 
25

Detection rates varied among States and due to differences in survey techniques, but 

generally were > 95 percent for both observers combined. 

The dual-frame sampling design can be applied throughout the contiguous United States 

in a manner similar to that conducted at the State level during the pilot studies. Using the 

dual-frame method to estimate population size throughout the contiguous U.S. will 

require close coordination with the States. Cooperation is needed to continually update 

the recently compiled nest list. Assistance from State biologists will be needed to ensure 

that bald eagle habitat is properly defined for each area and to confirm or modify the 

stratification. Experienced bald eagle observers will be needed to conduct the surveys. If 

experienced State pilots will be used for surveying, coordination and effort will be 

needed to set up the recording hardware and software and implement the double observer 

protocol. Finally, biologists familiar with the nest lists will be especially helpful in 

surveying nests on the list and in reconciling the observations in the area survey with 

those in the list. 

Goals of Sampling

The goal of post-delisting monitoring is to estimate changes in the number of occupied 

bald eagle nests in the contiguous 48 States. Because bald eagle populations have been 

increasing over most of their range, changes in rate of increase may be an important first 

indicator, and can be estimated by comparing the result from any two sample periods. 

This survey methodology is designed to detect a 25 percent relative population decline in 

the total number of occupied nests in the contiguous 48 States between any two sampling 

periods 80 percent of the time with a 10 percent chance of getting a significant decline 

just by chance. Statistical methods and pilot data described here provide a rigorous 

framework for predicting the number of areas that need to be sampled to meet this goal. 

Stratification

Bald eagle distribution and nesting density varies widely both within and among States. 

The Plan uses physiographic regions developed for bird conservation (Bird Conservation 

Regions, or BCRs; U.S. North American Bird Conservation Initiative Monitoring 

Subcommittee 2007) as strata for developing eagle survey plots throughout the 

contiguous United States. The BCRs group regions with similar habitats and other 

environmental features, and allow for a more consistent regional grouping of habitats 

than State boundaries. 

To accommodate State-specific needs, we divided BCRs into States (e.g., we considered 

DE, MD Coastal Plain as a separate stratum from VA Coastal Plain), and used these 

State-BCR units as initial strata (Figure 1). Washington, Oregon, Florida and Maine have 

tailored their State strata based on their biologists’ knowledge. We then aggregated these 

State-BCR units to larger strata using a clustering procedure that assessed similarity in 

the State-BCR units from information on eagle abundance (Table 1). For each StateBCR, the eagle nest list data were overlain on a 10 km x 10 km grid (corresponding to the 

proposed plot size) and used to estimate mean and variance of eagle nests in Table 2. 
26

After each combining, the overall standard error could be assessed, and large increases in 

overall standard error indicate a lack of value in the grouping. In this analysis, we chose 

to stop combining when 18 State-BCRs remained as separate strata, and we combined the 

aggregated units into a low-abundance stratum. We further separated the 18 contiguous 

lowest density strata into a “trace” stratum, a region containing only 14 nests in the 

stratum (Figure 2). We view these aggregate strata as reasonable regions for 

implementing an initial survey design. Aggregating the similar strata will improve the 

estimation by avoiding imprecisely estimating numbers of nests in many small strata. 

Variation in plot densities in the aggregated strata is still higher than we would expect for 

count data. This suggests that further stratification would be useful. State biologists, 

particularly those in States containing the 18 primary strata are encouraged to refine these 

strata using their knowledge of eagle populations and habitat use by the species. Also, if 

amount of habitat or shoreline are highly correlated with density of occupied nests, we 

should weight the sample selection by the correlated variables. Finally, we can obtain 

sub-regional or other small area occupied nest estimates (e.g., estimates in portions of 

aggregated strata) by post-stratification (Lohr 1999, p. 114) or small-area estimation 

(Lohr 1999, p. 397). 

List Frame

State biologists have provided lists of nests with their locations, last known status, and 

year of the observation. The list frame can be sampled or censused to estimate the 

number of known nests that are occupied. Sampling from the list frame is efficient 

because locations are known and nests can be observed by flying directly from one nest 

to the next. Figure 3 illustrates the distribution of nests collated from State lists. 

Because sampling the list is a major cost associated with an eagle monitoring program, 

we explored an approach to grouping the list nests for sampling. Efficiency can be 

gained by grouping the nests from the lists into “clusters,” then sampling the clusters of 

nests in conjunction with the area component of the survey. Clustering increases the 

variance relative to a random sample, but this should be compensated by the reduced cost 

of sampling (Lohr 1999, pp 154). 

To implement this approach, we suggest that the list sampling be directly connected to 

the area sampling, by treating the area sample units (the plots) as clusters. List frame 

nests within a plot can be defined as a cluster. During the area sample, if a plot is 

selected for the survey, all list nests in that plot will also be sampled as the cluster. 

Sampling the list where we sample the area allows us best to assess the coverage of the 

list and correctly assess nests as occupied or unoccupied. For the rest of this appendix, 

sampling of the list frame will be done on clusters of list nests within a plot. Plots with 

list nests will be the list frame sampling unit. 
27

Area Frame

Within strata, we suggest that the sample unit for area sampling be the 10 km x 10 km 

plots used in the pilot studies. For development of a sampling frame for the contiguous 

48 States, we used ArcGIS with a Lambert Equal-Area Projection to generate 10 km x 10 

km plots. The plots were then categorized by strata. Non-US and water portions of plots 

on the coasts or Mexican and Canadian borders were removed. Plots that overlapped two 

or more strata were assigned to the stratum that had the majority area. Figure 4 is an 

example of the plot grid from the pilot study in Missouri. Filled blocks represent the 

selected sample plots; the diamonds indicate location of selected sample list nests. 

The 10 km x 10 km grid spanning the contiguous United States was overlain on a map of 

the list nest locations, associating each nest with a plot, and means and variances of 

number of nests per plot were calculated for each of the strata. These data form the 

fundamental information for allocation of samples. 

Estimation and Detectability

For estimation and survey design, we follow Haines and Pollock’s (1998) methods and 

add additional components for estimating detection probability. We estimate the total 

number of occupied nests, NLi , by adding the estimated nests in the list, YLi

ˆ , and the 

estimated number of occupied nests in the area frame that were not in the list frame, . 

We use the subscript N instead of A because the nests are new. The stratum estimates are 

added up to get the national total, 

 LI AI

i

Ni

I

i

Li YYY ˆˆˆ

The L I list or AL I area strata can be different. The list strata effectiveness is determined 

by the differences in the percent occupied and the area strata effectiveness by the 

differences in the density of the new nests. The latter is determined by unknown 

variation in the list coverage along with the occupied nest density itself. 

The estimate for occupied nests in the list frame is the sample proportion of occupied 

nests, Li y , expanded by the number of nests in the stratum, Li LiLi yNY ˆ ˆ  . 

 

The estimate for new occupied nests expands the density of the new nests seen, Ni y , by 

the stratum size, , and the detection probability, , 

i

NiAi

Ni

p

yN Y ˆ

ˆ 

The A stands for the area frame. The higher the density of occupied nests, the larger the 

stratum area, and the lower the detection probability, the larger the stratum total. 
28

The variances from the list and area frames are independent, so they can be added to get 

the variance of the total1, 

       LI AI

i

Ni

I

i

Li YVarYVarYVar ˆ ˆ ˆ

If the list is censused, the variance associated with its estimate is 0. If it is sampled, the 

stratum variances for the list frame only depend on the number of occupied nests, NLi , 

and the variability of the estimate,    1/1  2

LiLiLi  nyynS LiLi  , and the sample size, nLi , 

    Fixed Part

n

SN YVar

Li

LiLi

Li _ ˆ 2



So the variance decreases as the number of occupied nests and the sample size increases. 

Components of the formula not needed for this analysis are indicted by the term “Fixed 

Part,”   2 Fixed _  SNPart LiLi . They represent the parts of the variance that are not 

affected by the sample size. 

Estimation of the stratum area frame variances is complicated by the detection 

probability. 

     

    Fixed Part

np

pVarnyN

np

SN

YVar

Aii

pNiA i

Aii

NiAi

Ni _ ˆ 1

1 ˆ

ˆ

ˆ 4

22

2

2

 

  . 

The variance decreases as the area ( NAi ) density of new nests ( Ni y ) the variance of the 

density of new nests ( 2 S Ni ) and variance of the detection probability    pVar i ˆ decrease 

and as the sample size ( nAi ) and the detection probability itself ( pi ˆ ) increases. Again, 

the “Fixed_Part” 

   

2

2 2

2

2

ˆ

1 ˆ

ˆ _

i

NiiA

i

NiAi

p

ypN

p

SN Fixed Part  

is a part of the variance that is not affected by the sample size. Note that the variance of 

the new nest density will drop as fewer new nests are found, i.e., if the list is more 

complete, the variability of the new nests drops. The parts of the variance that change 

with sample size are used in estimating the required sample size. 

Survey Design

To design a survey, we calculate the variances we require given our sampling goals and 

look at alternative designs to attain those goals by comparing the sample sizes and 

resulting costs needed. The effect size (in terms of relative change), power, significance 

level, and variability of the data determine the variance needed from the survey. We use 

 

1

 We use variances when we derive the sample sizes we need because the variances of 

independent parts of the survey can be added. The standard errors are the square roots of 

the variance. We use them in the tables and graphs because they are more understandable 

in that they are used to construct confidence intervals. They are on the same scale as the 

data. 
29

these components to define the least expensive allocation of samples that meets our 

variance requirements. We would like to minimize both the costs and the variance, 

       Y AiLi AiLi min ,nnVar ,nnCost ˆ 

The variance, Y Varˆ , is the variance of the total in the previous section. The variance and 

cost are written as functions of the list and area sample sizes nLi and nAi , as both 

parameters depend on sample size. 

Costs also vary by stratum. We approximate the cost of sampling a stratum with a linear 

function, 

  , ( ) 0 AiAiLi

L

i

AiLi   Li  ncnccnnCost , 

where the total cost is the sum of 0 c , the fixed cost for both the list and area frames, Li c , 

the cost of adding another nest or nest cluster to the list sample and Ai c is the cost of 

adding another area sample. 

The Lagrangian Multiplier, , represents the trade off between cost and variance. When 

we change the sample sizes we decrease the variance because we are taking a larger 

sample and also paying the cost of it. Among all the strata there is some consistent 

tradeoff between reducing the variance and increasing the cost,  . The solution to the 

minimization of the cost-variance function, requires more sampling in the strata that for 

the best price will get the best reduction in variance. The sample is said to be optimally 

allocated among the strata. 

Since we solve the multiplier for the sample size, the stratum nest densities and their 

variances are input, forming the “data” used in the equations. We use the estimates 

derived from the nest list and pilot studies (Table 2). Likewise, we also use the nest list 

data to construct cost functions for sampling. These calculations yield optimal sampling 

procedures, given the pilot data that are input. Following most sampling texts, we 

suggest choosing sample sizes 10 percent more than the minimum recommended from 

the optimal allocation. 

We compare four designs: 

1. List-only, 

2. Area-only, 

3. Dual-frame, and 

4. Combined dual-frame. 

1. List-only. The current information comes from the State nest list. A “List-only” 

design would involve sampling only from these nest lists without any attempt to estimate 

the number of nests missing from the list. The estimates can be derived by just using the 

terms in the total and variance equations that have to do with the list. The list estimate is 
30

always biased, as occupied nests always exist that are not on the list. Magnitude of the 

bias can be expressed as the list coverage, which is the number of nests on the State nest 

lists as a percentage of the total nests. We include this bias when comparing the sample 

designs by making the estimate of variability the mean squared error, 

  2 bias mse YVar ˆ

l  . 

2. Area-only. The area-only design ignores the State nest lists and estimates the number 

of occupied nests using just the nests found on a random sample of the plots. The area 

estimate uses only the terms for the area survey in the total and variance equations. All 

the nests in the plots are used, not just the new nests. This estimate is unbiased. 

3. Dual-frame. The dual-frame design includes both the list and the new nests in the area 

survey. The total and variance equations are shown above. 

4. Combined dual-frame. Finally, we include a special case of the dual-frame called the 

combined dual-frame where the list nests are sampled immediately after sample plots. 

This could save on flight time. The equations are the same as for the dual-frame, but the 

size of the list frame sample is the number plots in the area sample times the portion of 

area plots that also are known to contain list nests plus an extra sample of list cluster 

plots. We use different cost functions because of the differences in sampling. 

Cost Functions for Sampling List-Plot Clusters

The cost functions for sampling the list are determined by simulation, drawing samples 

and calculating the shortest distance needed to travel among all the sample clusters plus 

the distances to travel within each cluster. Samples of different sizes are drawn, the 

distance for the minimum spanning tree is summed for each sample, and a regression is 

done with flight miles against sample size. A number of samples of different sizes were 

estimated for each stratum using the contiguous 48 State nest list. Cost functions are 

derived by a linear regression allowing equations for each stratum to be different. The 

totals of the distances traveled among given locations are determined from their minimal 

spanning trees (Paradis 2004, the mst function). Minimal spanning trees do not account 

for flights starting and returning to one or more airports for each flight. 

The distances traveled during the pilot surveys can be converted to costs by assuming the 

planes flew 100 miles per hour and the cost of the plane was a rate of $317 per hour (the 

Service rate in 2007). Because the conversion factor varies with flight fuel and other 

costs that will probably increase before implementation, we use flight miles as our 

measure. Actual costs can be applied post hoc using relevant costs. The relative rates do 

not change. Only flight miles are accounted for in this analysis. Other costs can be 

added on to those found here to make more realistic estimates. As cost estimates per list 

cluster or plot are revised, the analysis should be revised. Figure 5 shows the number of 

miles needed to fly samples of a given number of list-plot clusters. There is a separate 

line for each stratum. Some lines do not extend as far as others because of their varying 

number of clusters. This is especially true for the trace stratum which only has 12 nests 

in 12 clusters; trace clusters are far apart, hence the line is very steep. The slope affects 
31

the proportion of the stratum that is sampled; the steeper the slope, the more expensive 

the sampling cost and the less it is likely to be sampled. The intercept affects the initial 

cost of sampling the stratum. Since all strata are sampled to some extent, the initial cost 

applies to a sample of any size. The other strata have lower, more similar slopes. 

Cost Functions for Sampling Plots

The cost functions for the plots in the area frame are similarly determined, see Figure 6. 

At a range of sample sizes, the minimum distances among the simulated sample plots are 

added to the within-plot costs for each plot. The within plot costs are determined from 

the length of the shoreline within each plot. We set a minimum value of 33 miles to scan 

a plot with little or no habitat. We also set an upper bound, assuming that complete 

coverage by dividing the plot into transects would be more efficient at some point; the 

upper bound is never reached. 

The linear cost functions are determined as in the list-plot cluster analysis, but here the 

samples are plots over the whole stratum. The plots occur more regularly than the list 

nests or plot clusters, so the differences in the stratum cost functions are due to the 

amount of shoreline in the plots and the size and shape of the stratum. For these cost 

functions, the cost of sampling the trace stratum is more expensive than sampling the low 

stratum. Costs of the other strata again are lower and generally similar among strata. 

The cost functions for the combined dual-frame design are not shown but are slightly 

higher than those shown in Figure 6. 

Proportion of Occupied Nest and List Coverage Simulations

Since we did not have consistent information from all States on the proportion of 

occupied nests or on list coverages in the High-density strata, we simulated values of 

occupied nests for each stratum between 0.35 and 0.7, and list coverages from 0.4 to 0.9. 

For the Low and Trace strata we assumed a much higher proportion of coverage (0.7 to 

0.98). We used these values in 100,000 simulations, in which proportions of occupied 

nests and list coverages were simulated for each stratum and the optimal sample 

allocation and cost-variance calculations were calculated. The ranges of values provided 

as results are based on the simulations. 

Optimal Stratum Allocation

As mentioned above, the optimal allocation of sampling effort to strata is independent of 

the overall sample size. Consequently, the allocations presented below represent the 

relative amount of effort to be allocated to each stratum. The percentages vary because 

of simulations due to unknown proportions of occupied nests and list coverage. In 

general, sample sizes increase for strata that are larger, more densely populated, more 

variable, with a lower detection probability, with a more variable detection estimate, and 

are less expensive to sample (Table 3). What is striking is the variation allocated to the 

list frame, 23 to 80 percent. If we knew list coverage to be high we would sample more 

of the list. 
32

The allocations for the area frame are shown in the second column of Table 3. Notice 

that trace and low strata are sampled lightly both in relation to proportional sampling and 

to the large size of those strata. Although large in area, the strata are very lightly sampled 

because they are not densely populated and are costly to sample. Almost two-thirds of 

the cost of the survey is due to sampling the Low and Trace strata. (14,000 miles are 

needed to sample the High-density strata while 26,000 miles are needed to sample the 

Low and Trace strata.) This highlights the need to sample the low and the trace strata 

efficiently. During the implementation of the survey, we suggest that the necessity of an 

area sample in the Low and Trace strata be evaluated. It is unlikely that such a sample 

will provide much useful information on eagle populations due to the low abundances of 

nests. In the Low stratum, targeting potential habitat (amount of habitat or shoreline near 

a given plot) could improve the sampling and estimation. Non-aerial sampling and 

citizen-science based approaches could greatly enhance the efficiency of the survey, 

especially in the Low stratum, and we recommend that these approaches be explored.

Survey Sample Design Comparison

With optimally allocated samples for each design, we can compare the three primary 

alternative designs (list-only samples, dual-frame samples, and combined sampling 

(sampling list clusters after the plots)) in two ways: (1) In terms of cost: what standard 

error (SE) can we obtain for a given total cost for each of the sampling designs, and (2) In 

terms of precision: what do we have to spend for each design if we require a given 

overall standard error. Figure 7 answers the first question. The list-only survey is the 

horizontal line on top. We use the mean squared error (MSE), which reflects both bias 

and variance. The MSE includes the square of the bias between the list estimate and the 

actual number of nests. The bias term dominates at the 60 percent list coverage we 

observed in the pilot studies. No amount of sampling will overcome it - even if all the 

strata are censused. Dual-frame sampling is more cost effective than area-only sampling 

in a survey of over 20,000 flight miles (Figure 7). There is not much difference between 

the dual-frame and the combined dual-frame sampling in terms of the standard error 

obtained for a given cost. 

Table 4 answers the second question: given certain precision requirements (setting 

differing levels of effect size (relative change), power, and significance level) for the 

estimates, what cost is needed to obtain such a requirement? The first case is the stated 

monitoring goals: a 25 percent relative change (effect size) detected 80 percent of the 

time (power) at a significance level of 10 percent (significance level). These 

specifications determine a required standard error. The cost is shown in the following 

columns for the list-only frame (list), plot or area-only frame (plot), dual-frame, and 

combined-dual-frame. The list-only flight miles are constant but the estimate obtained 

will always be biased with no way to determine the bias. The dual-frame estimates are an 

improvement over the area-only frame, with the combined dual-frame design being 

slightly more efficient. In practice, the economies associated with the combined 

sampling may be greater. 
33

These costs represent minimum costs. They do not take into account search time for 

nests, flights to and from airports, weather days and per diem for pilots and observers, 

differences in flight rates among regions, equipment and preparation costs. Survey 

planners should add additional funding to accommodate these incidental costs. 

Table 5 shows example sample sizes by State for the proposed survey goals. These will 

change as we work with the States to refine the stratification and sampling methods 

especially in the Low and Trace strata. Figure 8 shows an example sample selection 

including area samples in all strata. 

Effects of List Coverage

The dual-frame design provides a way to assess the coverage of the list. The area frame 

is used to estimate the number of new (i.e., not in the list) nests, and hence to estimate the 

list coverage. The variance of the new nests is the major contribution to the variance of 

the total. The list coverage (that is, the proportion of actual nests that are in the list) 

affects the relative efficiency of the designs. 

Figure 9 shows how the standard error changes for given list coverage when the survey 

requirements are the stated survey goals. The dual-frame is better than an area (plotbased) survey only, as list coverage is over 40 percent. The difference improves as the 

list coverage improves. The list approaches the dual-frame standard errors as the 

coverage approaches 100 percent. Note that an evaluation based only on the list coverage 

is problematic without area-based sampling to assess the coverage. That is the value of 

dual-frame sampling. It allows an assessment of the list coverage, and permits estimation 

of actual numbers of occupied nests. 

The optimal allocation treats the same strata in the list and area frames as different strata, 

i.e., the Central Florida stratum has a sample of list plots and a sample of area plots. 

These are treated as if they are in different strata. It then allocates sampling effort to 

each. Because the variability of the list-frame is so much less than the area frame, most 

of the sampling effort is allocated to the area-frame. Figure 10 shows the proportion of 

flight miles allocated to the list as the list coverage improves. We use cost because it is 

the common denominator between the two frames. The cost allocated to the list increases 

as the list coverage improved but the costs only vary noticeably when list coverage is 

greater than 90 percent. As the cost of the plot frame increases or the plot standard 

deviations improve relative to the list frame, more effort (as cost) is allocated to the list 

more quickly (red and green lines). The large allocation to the area frame indicates the 

importance of reducing the variability in the plot sample. 

Misclassification of Occupied Nests

We use the definition of occupied nests from this Post-delisting Monitoring Plan for the 

Bald Eagle (p.15–16). Nests in repair were able to be distinguished by each of the State 

crews in the pilot study. Fly backs or other methods can be used to verify the nest 
34

condition. If an empty nest condition cannot be assessed, the nest is classified as 

unoccupied. This provides a conservative estimate of occupied nests. 

In those cases where the list survey is conducted separately from the area survey, at least 

two independent observations of occupancy can be obtained. Occupancy should be 

recorded separately for each visit. The area survey should be run early in the breeding 

season when the pairs are most tightly bound to the nest. A Lincoln-Peterson estimate 

can assess the number of nests where occupancy is missed on both visits. If the status of 

the nest is determined outside the surveys, that better assessment of the status may be 

used for that observation, but only observations from the list and area surveys should be 

used in Lincoln-Peterson estimate and in the survey total variance calculations. 

Conclusions 

The goal of the post-delisting monitoring survey is to estimate the change in occupied 

bald eagle nests in the contiguous 48 States. To achieve this goal, we use the procedures 

outlined above for deciding on strata, clustering nests from the contiguous 48 State nest 

list, optimally allocating samples to strata for both the list and plot surveys, and randomly 

selecting samples according to that optimal allocation. We estimate sample sizes to 

obtain estimates with a given power and precision or within given costs. We use the 

dual-frame procedure with a double observer technique in the plot survey to sample more 

efficiently, resulting in the reduction of less than half the flight miles. We combine 

sampling list clusters with the area plots survey to better assess coverage of the list. 

Finally, we use independent estimates of occupancy to assess the number occupied of 

nests missed in both the list and area samples. 
35

References 

Bartish, TM. 1994. Design Considerations for Trust Species Monitoring: Bald Eagles 

and Their Habitat in the Great Lakes Region. U.S. Geological Survey, Biomonitoring 

of Environmental Status and Trends Program Pilot Project Report, December 1994. 

45 pp. 

Grier, J.W. and J.E. Guinn. 2003. Bald Eagle Habitats and Responses to Human 

Disturbance in Minnesota: Final Report. Unpublished Report. Final report to the 

Minnesota Department of Natural Resources, Natural Heritage and Nongame Wildlife 

Program, Division of Ecological Sciences. St. Paul, Minnesota. 44 pp. 

http://files.dnr.state.mn.us/eco/nongame/projects/consgrant_reports/2003/2003_grier_

guinn.pdf. 

Haines, D. E., and K. H. Pollock. 1998. Estimating the number of active and successful 

bald eagle nests: an application of the dual-frame method. Environmental and 

Ecological Statistics 5:245-256. 

Nichols, J. D. J. E. Hines, J. R. Sauer, F. W. Fallon, J. E. Fallon, and H. J. Heglund. 

2000. A double-observer approach for estimating detection probability and 

abundance from point counts. Auk 117(2):393–408. 

Lohr, S.L., 1999. Sampling: Design and Analysis. Brooks/Cole Publishing Co., 

Washington, DC. 494 pp. 

Paradis E., Claude J. & Strimmer K. 2004. APE: analyses of phylogenetics and evolution 

in R language. Bioinformatics 20: 289–290. PDF, cran.rproject.org/web/packages/ape/ape.pdf 

Sauer, J. R., W. A. Link, J. D. Nichols, and J. A. Royle. 2005. Using the North 

American Breeding Bird Survey as a tool for conservation: A critique of Bart et al. 

(2004). Journal of Wildlife Management 69(4):1321–1326. 

Thompson, S. K. 1992. Sampling. John Wiley & Sons, Inc., New York, New York. 

343 pp. 

Thompson, W. L. 2004. Sampling Rare or Elusive Species. Island Press., Washington, 

DC. 429 pp. 

U.S. North American Bird Conservation Initiative Monitoring Subcommittee. 2007 

Opportunities for Improving Avian Monitoring. U.S. North American Bird 

Conservation Initiative Report. 50. pp. Division of Migratory Bird Management, 

U.S. Fish and Wildlife Service, Arlington, VA; www.nabci-us.org. 
36

Tables 

Table 1. Aggregating or merging sequence of adjacent strata. Stratum 1 and 2 are the two 

strata to be combined. “Edge” is the name the combination strata are given. “SE” is the 

standard error of the survey total of the combination. The start is the individual State 

BCRs. Note the SE does not noticeably change until after Edge.156.
37
38

Table 2. Summary statistics of State-BCRs with the number of nests, plot, density per 10 km x 

10 km, and standard error of the density. Density is determined from nest list nests. The 

larger, higher density strata will be sampled much more intensely. It is also encouraging 

that portions of BCRs in different States have similar plot densities. This suggests that 

the BCR stratification is effective.

State Bird Conservation Region Nests Plots Density SE 

Wisconsin Boreal Hardwood Transition 1635 481 3.40 4.730 

Washington Northern Pacific Rainforest 2002 612 3.27 5.635 

Virginia Southeastern Coastal Plain 473 189 2.50 4.203 

Virginia New England/Mid-Atlantic Coast 159 75 2.12 3.251 

Maryland New England/Mid-Atlantic Coast 363 200 1.82 2.624 

Iowa Prairie Hardwood Transition 129 73 1.77 2.880 

Michigan Boreal Hardwood Transition 1654 1007 1.64 2.806 

Illinois Mississippi Alluvial Valley 6 4 1.50 1.732 

Florida Peninsular Florida 1513 1105 1.37 2.799 

Kentucky Mississippi Alluvial Valley 13 11 1.18 0.982 

Minnesota Boreal Hardwood Transition 1084 937 1.16 2.165 

Maine Atlantic Northern Forest 1055 919 1.15 2.909 

Pennsylvania New England/Mid-Atlantic Coast 2 2 1.00 0.000 

Oregon Northern Pacific Rainforest 657 851 0.77 2.364 

Louisiana Mississippi Alluvial Valley 315 410 0.77 2.333 

Tennessee Mississippi Alluvial Valley 16 21 0.76 1.513 

Michigan Eastern Tallgrass Prairie 31 46 0.67 2.023 

Minnesota Prairie Hardwood Transition 273 497 0.55 1.216 

Oregon Great Basin 529 1156 0.46 2.818 

Wisconsin Prairie Hardwood Transition 446 998 0.45 1.363 

Illinois Prairie Hardwood Transition 13 32 0.41 1.012 

Washington Northern Rockies 93 242 0.38 0.996 

South Carolina Southeastern Coastal Plain 206 543 0.38 1.040 

Montana Northern Rockies 503 1596 0.32 1.012 

Florida Southeastern Coastal Plain 167 584 0.29 0.794 

New Jersey New England/Mid-Atlantic Coast 42 147 0.29 0.672 

South Dakota Eastern Tallgrass Prairie 9 33 0.27 0.944 

Nevada Sierra Nevada 2 8 0.25 0.463 

Illinois Central Hardwoods 42 183 0.23 0.622 

Michigan Prairie Hardwood Transition 139 611 0.23 1.119 

Iowa Eastern Tallgrass Prairie 245 1082 0.23 0.955 

Connecticut Atlantic Northern Forest 2 9 0.22 0.441 

Minnesota Eastern Tallgrass Prairie 22 111 0.20 0.989 

Ohio Eastern Tallgrass Prairie 94 527 0.18 0.742 

Pennsylvania Lower Great Lakes/ St. Lawrence Plain 15 89 0.17 0.482 

California Great Basin 62 400 0.16 0.471 

Virginia Piedmont 65 421 0.15 0.815 
39

State Bird Conservation Region Nests Plots Density SE 

Nebraska Eastern Tallgrass Prairie 34 221 0.15 0.480 

Missouri Mississippi Alluvial Valley 15 102 0.15 0.534 

Nebraska Prairie Potholes 23 159 0.14 0.488 

New Hampshire New England/Mid-Atlantic Coast 6 42 0.14 0.417 

Ohio Lower Great Lakes/ St. Lawrence Plain 32 230 0.14 0.416 

Indiana Central Hardwoods 49 355 0.14 0.391 

Iowa Prairie Potholes 42 308 0.14 0.758 

Montana Badlands And Prairies 186 1395 0.13 0.681 

Arkansas Mississippi Alluvial Valley 52 395 0.13 0.573 

Kentucky Southeastern Coastal Plain 5 39 0.13 0.522 

Maryland Piedmont 9 71 0.13 0.412 

South Carolina Piedmont 34 273 0.12 0.492 

Minnesota Prairie Potholes 81 699 0.12 0.472 

Idaho Northern Rockies 122 1059 0.12 0.458 

Georgia Southeastern Coastal Plain 109 949 0.11 0.491 

Georgia Piedmont 48 424 0.11 0.452 

Colorado Northern Rockies 10 92 0.11 0.346 

Pennsylvania Piedmont 13 121 0.11 0.337 

Louisiana Gulf Coastal Prairie 39 367 0.11 0.545 

California Sierra Nevada 55 520 0.11 0.459 

Oklahoma West Gulf Coastal Plain/Ouachitas 29 295 0.10 0.445 

Arkansas West Gulf Coastal Plain/Ouachitas 63 650 0.10 0.435 

Texas West Gulf Coastal Plain/Ouachitas 67 712 0.09 0.676 

Missouri Central Hardwoods 79 871 0.09 0.345 

Kentucky Central Hardwoods 62 699 0.09 0.536 

North Carolina Southeastern Coastal Plain 63 714 0.09 0.308 

Alabama Appalachian Mountains 32 374 0.09 0.363 

Washington Great Basin 86 1006 0.09 0.410 

Mississippi Mississippi Alluvial Valley 17 201 0.08 0.397 

Oklahoma Eastern Tallgrass Prairie 13 154 0.08 0.322 

Massachusetts New England/Mid-Atlantic Coast 16 201 0.08 0.366 

New Jersey Appalachian Mountains 3 38 0.08 0.273 

California Northern Pacific Rainforest 38 485 0.08 0.355 

South Dakota Central Mixed Grass Prairie 1 13 0.08 0.277 

Wyoming Northern Rockies 127 1651 0.08 0.410 

New Jersey Piedmont 3 40 0.08 0.267 

Tennessee Central Hardwoods 30 403 0.07 0.330 

Alabama Piedmont 4 55 0.07 0.262 

Utah Northern Rockies 2 28 0.07 0.378 

Oregon Northern Rockies 38 541 0.07 0.378 

Connecticut New England/Mid-Atlantic Coast 8 118 0.07 0.252 

Wisconsin Eastern Tallgrass Prairie 1 16 0.06 0.250 

Nebraska Central Mixed Grass Prairie 73 1220 0.06 0.247 
40

State Bird Conservation Region Nests Plots Density SE 

New Hampshire Atlantic Northern Forest 11 200 0.06 0.287 

Illinois Eastern Tallgrass Prairie 66 1238 0.05 0.288 

Alabama Southeastern Coastal Plain 43 845 0.05 0.250 

Ohio Central Hardwoods 1 20 0.05 0.224 

Tennessee Appalachian Mountains 19 412 0.05 0.221 

Idaho Great Basin 50 1100 0.05 0.269 

Missouri Eastern Tallgrass Prairie 35 825 0.04 0.264 

Wyoming Badlands And Prairies 27 646 0.04 0.249 

Oklahoma Central Hardwoods 3 75 0.04 0.197 

North Carolina Piedmont 17 458 0.04 0.231 

Alabama Central Hardwoods 3 82 0.04 0.189 

Ohio Appalachian Mountains 11 310 0.04 0.202 

Massachusetts Atlantic Northern Forest 2 58 0.03 0.184 

South Dakota Prairie Potholes 28 880 0.03 0.205 

Louisiana West Gulf Coastal Plain/Ouachitas 15 474 0.03 0.175 

Oklahoma Oaks And Prairies 13 418 0.03 0.199 

North Dakota Badlands And Prairies 17 549 0.03 0.265 

Arizona Sierra Madre Occidental 30 972 0.03 0.179 

Colorado Southern Rockies/Colorado Plateau 45 1473 0.03 0.184 

Kansas Eastern Tallgrass Prairie 20 662 0.03 0.180 

Arkansas Central Hardwoods 10 332 0.03 0.256 

Indiana Eastern Tallgrass Prairie 13 448 0.03 0.168 

Montana Prairie Potholes 24 869 0.03 0.248 

California Coastal California 46 1773 0.03 0.263 

Mississippi Southeastern Coastal Plain 27 1047 0.03 0.219 

Nebraska Shortgrass Prairie 9 350 0.03 0.159 

Louisiana Southeastern Coastal Plain 2 78 0.03 0.159 

Colorado Shortgrass Prairie 28 1129 0.02 0.167 

Rhode Island New England/Mid-Atlantic Coast 1 42 0.02 0.154 

North Dakota Prairie Potholes 31 1316 0.02 0.256 

Maryland Appalachian Mountains 1 46 0.02 0.147 

Pennsylvania Appalachian Mountains 20 966 0.02 0.142 

South Dakota Badlands And Prairies 21 1037 0.02 0.148 

Nebraska Badlands And Prairies 1 52 0.02 0.139 

Georgia Appalachian Mountains 3 162 0.02 0.135 

Delaware New England/Mid-Atlantic Coast 1 57 0.02 0.132 

Kentucky Appalachian Mountains 5 302 0.02 0.190 

Virginia Appalachian Mountains 6 401 0.01 0.122 

Arizona Sonoran And Mojave Deserts 15 1060 0.01 0.159 

Tennessee Southeastern Coastal Plain 3 251 0.01 0.109 

Texas Gulf Coastal Prairie 5 521 0.01 0.158 

Vermont Atlantic Northern Forest 2 211 0.01 0.097 

Wyoming Shortgrass Prairie 1 126 0.01 0.089 
41

State Bird Conservation Region Nests Plots Density SE 

Indiana Prairie Hardwood Transition 1 133 0.01 0.087 

New Mexico Sierra Madre Occidental 2 285 0.01 0.084 

Utah Southern Rockies/Colorado Plateau 9 1320 0.01 0.113 

Oklahoma Central Mixed Grass Prairie 4 757 0.01 0.073 

Utah Great Basin 3 851 0.00 0.059 

New Mexico Shortgrass Prairie 2 677 0.00 0.054 

New York Appalachian Mountains 1 379 0.00 0.051 

Kansas Central Mixed Grass Prairie 2 1102 0.00 0.043 

Texas Oaks And Prairies 2 1521 0.00 0.036 

New Mexico Chihuahuan Desert 1 878 0.00 0.034 

Nevada Great Basin 2 2466 0.00 0.028 

New Mexico Southern Rockies/Colorado Plateau 1 1326 0.00 0.027 

West Virginia Appalachian Mountains 0 628 0.00 0.000 

Delaware Piedmont 0 1 0.00 0.000 

Arizona Chihuahuan Desert 0 12 0.00 0.000 

Texas Chihuahuan Desert 0 1044 0.00 0.000 

Utah Sonoran And Mojave Deserts 0 4 0.00 0.000 

Connecticut Appalachian Mountains 0 11 0.00 0.000 

Texas Shortgrass Prairie 0 1047 0.00 0.000 

Arizona Southern Rockies/Colorado Plateau 0 937 0.00 0.000 

Vermont Lower Great Lakes/ St. Lawrence Plain 0 45 0.00 0.000 

California Sonoran And Mojave Deserts 0 1056 0.00 0.000 

Texas Tamaulipan Brushlands 0 719 0.00 0.000 

Texas Edwards Plateau 0 588 0.00 0.000 

New York New England/Mid-Atlantic Coast 0 84 0.00 0.000 

Mississippi Gulf Coastal Prairie 0 3 0.00 0.000 

Wyoming Southern Rockies/Colorado Plateau 0 108 0.00 0.000 

Massachusetts Appalachian Mountains 0 7 0.00 0.000 

Nevada Sonoran And Mojave Deserts 0 389 0.00 0.000 

Nevada Southern Rockies/Colorado Plateau 0 3 0.00 0.000 

Maine New England/Mid-Atlantic Coast 0 30 0.00 0.000 

New York Atlantic Northern Forest 0 294 0.00 0.000 

Kansas Shortgrass Prairie 0 372 0.00 0.000 

Kansas Oaks And Prairies 0 3 0.00 0.000 

Kansas Central Hardwoods 0 1 0.00 0.000 

Texas Central Mixed Grass Prairie 0 888 0.00 0.000 

North Carolina Appalachian Mountains 0 213 0.00 0.000 

Ohio Prairie Hardwood Transition 0 1 0.00 0.000 

Oklahoma Shortgrass Prairie 0 113 0.00 0.000 

Idaho Southern Rockies/Colorado Plateau 0 6 0.00 0.000 

South Carolina Appalachian Mountains 0 19 0.00 0.000 

South Dakota Shortgrass Prairie 0 23 0.00 0.000 

New York Lower Great Lakes/ St. Lawrence Plain 0 581 0.00 0.000 
42

Table 3. The range of percent of the total sample allocated to both the list and area frame. 

The percentages are those within each frame. The first line indicates the allocation of the 

flight miles (cost) to each frame. The percentages are reversed for the area frame to 

emphasize that resources are the complements of each other. The variation in list 

coverage causes a large variation in allocation to each frame. Improved list coverage 

results in increased allocation to the list frame.

Stratum BCR Name List Area 

FL Peninsular Florida 2.5- 8.8 7.8-2.1 

IA Prairie Hardwood Transition 0.2- 0.6 0.8-0.2 

IL Prairie Hardwood Transition 0.0- 0.1 0.1-0.0 

LA Mississippi Alluvial Valley 0.5- 1.9 3.0-0.8 

Low 5.2-18.5 16.1-1.8 

MD New England/Mid-Atlantic Coast 0.6- 2.3 1.7-0.4 

ME Atlantic Northern Forest 1.8- 6.4 7.5-0.9 

MI Boreal Hardwood Transition 2.1- 7.6 7.1-1.8 

MN Boreal Hardwood Transition 1.8- 6.4 5.2-1.3 

MN Prairie Hardwood Transition 0.9- 3.2 2.1-0.5 

MT Northern Rockies 0.9- 3.1 3.5-0.9 

OR Great Basin 0.4- 1.3 4.8-1.3 

OR Northern Pacific Rainforest 0.8- 2.8 3.5-0.9 

SC Southeastern Coastal Plain 0.6- 2.3 2.1-0.6 

Trace 0.0- 0.0 0.3-0.1 

VA New England/Mid-Atlantic Coast 0.3- 1.2 0.8-0.2 

VA Southeastern Coastal Plain 0.5- 1.7 2.4-0.6 

WA Northern Pacific Rainforest 1.0- 3.7 5.3-1.4 

WI Boreal Hardwood Transition 1.4- 4.9 5.6-1.4 

WI Prairie Hardwood Transition 1.0- 3.6 4.2-1.1 

Percent allocation to each frame 23-80 77-20 

. 
43

Table 4. Flight miles (thousands) needed to obtain a sample with given precision 

requirements for an estimate of the total for the four survey options (DF is dual-frame). 

The standard errors are those needed to obtain the required effect size, power, and 

significance level requirements. The list-only survey is not continued beyond the first 

survey requirements because even censusing the list does not reduce the bias due to 

incomplete coverage. Thus, a list-only survey cannot meet any of the survey 

requirements. 

Precision Power Sig-Lvl SE List Plot DF Comb-DF 

0.25 0.8 0.10 1,133 16 186 40 39 

0.25 0.8 0.05 1,006 230 46 45 

0.25 0.8 0.01 825 327 59 58 

0.25 0.9 0.10 963 249 48 48 

0.25 0.9 0.05 869 298 55 54 

0.25 0.9 0.01 731 402 70 69 

0.15 0.8 0.10 680 453 78 77 

0.15 0.8 0.05 604 550 94 93 

0.15 0.8 0.01 495 745 129 127 

0.15 0.9 0.10 578 589 101 99 

0.15 0.9 0.05 522 689 119 117 

0.15 0.9 0.01 438 883 158 155 

0.1 0.8 0.10 453 843 149 147 

0.1 0.8 0.05 402 989 181 178 

0.1 0.8 0.01 330 1,252 251 247 

0.1 0.9 0.10 385 1,044 195 191 

0.1 0.9 0.05 348 1,180 230 226 

0.1 0.9 0.01 292 1,419 305 300 
44

Table 5. The list and area columns show the mean and (range) of the sample sizes for 

each stratum for the proposed survey goal. Results are based on simulated list coverages 

and percent occupied nests because we did not have information for each stratum. Note 

that part of the list sample will be from the area plots that have list nests. List nests in the 

area plots become part of the list sample. 

Stratum BCR Name List Area 

FL Peninsular Florida 14 ( 8-24) 18 (2-61) 

IA Prairie Hardwood Transition 1 ( 1- 2) 2 (1- 7) 

IL Prairie Hardwood Transition 1 ( 1- 1) 1 (1- 2) 

LA Mississippi Alluvial Valley 3 ( 2- 6) 7 (1-26) 

Low 28 (16-49) 29 (2-94) 

MD New England/Mid-Atlantic Coast 4 ( 2- 6) 4 (1-14) 

ME Atlantic Northern Forest 10 ( 6-17) 17 (2-62) 

MI Boreal Hardwood Transition 12 ( 7-20) 16 (2-53) 

MN Boreal Hardwood Transition 10 ( 6-17) 12 (2-42) 

MN Prairie Hardwood Transition 5 ( 3- 9) 5 (1-18) 

MT Northern Rockies 5 ( 3- 9) 8 (1-29) 

OR Great Basin 2 ( 2- 4) 11 (2-41) 

OR Northern Pacific Rainforest 5 ( 3- 8) 8 (1-29) 

SC Southeastern Coastal Plain 4 ( 2- 6) 5 (1-19) 

Trace 1 ( 1- 1) 1 (1- 3) 

VA New England/Mid-Atlantic Coast 2 ( 1- 4) 2 (1- 7) 

VA Southeastern Coastal Plain 3 ( 2- 5) 6 (1-20) 

WA Northern Pacific Rainforest 6 ( 4-10) 12 (2-43) 

WI Boreal Hardwood Transition 8 ( 5-13) 12 (2-43) 

WI Prairie Hardwood Transition 6 ( 4-10) 10 (2-37) 
45

Figures 

Figure 1: State boundaries and Bird Conservation Regions (BCRs) in the 

contiguousUnited States 
46

Figure 2: Strata after aggregating adjacent strata with similar nest densities. The 

aggregate strata are: Trace with only 14 nests in the stratum (light green); Low (the result 

of aggregating the similar low density strata, yellow); Washington and Oregon Northern 

Pacific Rainforest; Washington, Idaho, and Montana Northern Rockies; North and 

Central Florida (South Florida is part of the Low stratum even though it is not adjacent to 

it); Iowa, Illinois and Wisconsin Prairie Hardwood Transition; Minnesota, Wisconsin, 

and Michigan Boreal Hardwood Transition; Mississippi Alluvial Valley in Louisiana; 

South Carolina Southeastern Coastal Plain; Delaware; Virginia and Maryland New 

England/Mid-Atlantic Coast; Virginia Southeastern Coastal Plain; and two Maine strata. 
47

Figure 3: Distribution of bald eagle nests as determined from 2004-2006 State lists. 
48

Figure 4: Missouri area frame consisting of 10 km square plots. Shaded squares are the 

sample plots selected. Diamonds are the list nests selected. 
49

Figure 5: Number of miles needed to fly samples of a given number of list-plot clusters. 

Each line represents an aggregate stratum. Low and Trace are aggregate strata with low 

densities of bald eagles. 
50

Figure 6: Number of miles needed to fly samples of a given number of plots. Each line 

represents an aggregate stratum. Low and Trace are aggregate strata with low densities 

of bald eagles. 
51

Figure 7: The standard error for a given flight miles for each sample design. The listonly design standard error is a mean square error that includes the bias squared. This bias 

is the major source of error and cannot be reduced by any amount of sampling, not even a 

census of the nest list. 
52

Figure 8: An example sample selection with sample sizes for the proposted survey 

requirements. The red samples are the list plot clusters, the blue are the area plots, and 

the green are the area plots also with the list nests. The sample sizes are not fixed for 

each State, only for the 20 strata. More information on the proportion of occupied nests, 

list coverage in each stratum and efficient ways to sample the Low and Trace strata will 

modify the allocation to better target sampling. 
53

Figure 9: Standard errors for a given list coverage for each of the survey design options. 

These were calculated given the survey requirements are the stated survey goals. Note 

that when the list coverage is 40 percent the dual-frame design is equivalent to the plotonly design. The list-only design converges with the dual-frame as the list coverage 

approaches 100 percent. Unfortunately with the list-only design, there is no measure of 

actual measure of list coverage. 
54

Figure 10: Proportion of the flight miles allocated to the list frame vs. the area frame 

given different list coverages. As the cost of the area frame increases and/or the 

variability decreases, more is allocated to list-frame as the two quicker rising curves 

show. 
55

Appendix 2 

 Bald Eagle Post-delisting Monitoring Standard Operating Procedures 

Based on the Maine Bald Eagle Pilot Project 

by John R. Sauer and Mark C. Otto 

Introduction

There are three potential types of aerial survey plots for the bald eagle post-delisting 

monitoring survey: list, area, and combined plots. 

List plots will be sampled if the State has not recently updated its nest list. In such cases, 

the status of all known nests will need to be observed and recorded for selected list plots. 

Potential bald eagle habitat in area plots will be scanned for any nests and on- or off-thenest bald eagles. The dual observer protocol described below is used for area plots to 

assess observer detection. 

Combined plots are area plots that also contain known list nests. These plots will first be 

flown as area plots (i.e. scan habitat for any nests using dual observer protocol), and then 

subsequently flown as list plots (i.e. return flight through plot to record status of all 

known nests). To avoid the potential for observers to search for known nests during the 

area plot portion of the survey, pilots and observers should not know which area plots are 

actually combined plots until after the area plot portion of the survey is complete (i.e. 

they complete the area plot survey and then turn over the map to reveal known nest 

locations). 

Area plot sampling requires that observers conduct independent counting in silence. 

Communication among observers waits until after an observation has been passed by the 

plane to identify what observers actually saw: the bird or nest. For each observation, 

information on who saw it and who did not see it should be recorded. If one of the 

counters is only participating in some of the data collection, they should be recorded as 

“not counting” for observations that occurred when they were not counting. 

This Standard Operating Procedure (SOP) is written assuming the rear seat observer is on 

the right side of the plane. Sitting behind the pilot is acceptable if needed, but it is 

preferable that the rear-seat observer be on the right side of the plane and count in tandem 

with the front-seat observer. In either case, the plane should be oriented, so the observers 

in tandem (front-back seat) are on the shoreward side or the side with better eagle habitat. 

Orienting the plane this way will facilitate counting in critical eagle habitat but should 

only be done when it does not require undue maneuvering or a safety hazard. To maintain 

independence of counts, the pilot should not orient the plane to make it easier for the rear 

observer to see eagles that the pilot has seen. If necessary, a screen should be added to 

prevent observers from seeing each other during counting. Also, front seat observers 

should not point out sightings as they occur so as to keep the observation independent. 

The observers sitting in tandem will implement the double observer counting procedure. 
56

Observations will not be noted by either observer until it is clear that the other observer 

has “missed” the observation. For the front-seat observer, this position should be when 

their view of the observation becomes obscured, which we define as an angle of 135 

degrees behind the observer. For the back-seat observer, this position will be after the 

observation passes 90 degrees (opposite their position). At this point, the observation 

will be described by the observer who made the observation, and it will be noted who 

among the crew (front-seat observer, rear-seat observer, pilot) saw the observation (of a 

single, pair, nest, juvenile). Note any discrepancies in the identifications of sightings. If 

needed, the aircraft can bank to verify the observation and collect additional information. 

For accurate GPS observations it is useful to circle before taking locations. 

If possible, the pilot will also be included as a third participant in the observations, 

although in interior transects the pilot will collect independent data (see below). 

Maps of area plots and list plots should be studied before the survey flights to plan 

potential flight routes. This will minimize potential confusion and maximize observation 

time during the survey. 

Information to be Collected

Information to be collected includes: nest, adult or immature eagle observations; which 

observers were looking, seeing, or missed the sighting; activity of individual birds 

(flying, perching, on nest incubating or not incubating); and nest status, (see sample data 

sheet, p. 61). A “capture history” format will be used to record whether each of the three 

observers actually saw an observation. The field will have three, single-character values 

that reflect the status of the observation for each of the three observers: pilot, front-seat 

observer, and rear-seat observer respectively. Status from an observer will be indicated 

as a “0” for not seen, a “1” for seen, and an “x” for not observing. For example, the entry 

"x01" would be entered when the pilot was not observing, the front observer did not see 

the observation, but it was seen by the rear observer. Observations by the pilot that were 

recorded on the left side of the aircraft would be coded “1xx.” Observations made by the 

dual observers when the pilot was not attempting to observe on the right side of the place 

would be either “x10,” “x01,” or “x11,” where x01 represents pilot not observing, not 

seen by front observer, but seen by rear-seat observer. 
57

Information to be collected has been coded into the data entry program (Table 1). Eagle 

ages and nest condition are to be entered as separate species codes: adult, immature, and 

unknown for off the nest, and empty, incubating, occupied (but not incubating), eggs, or 

eaglets for a nest sighting. Location off the nest can be flying, perching, or on nest, and 

the location on the nest identifies the nest tree type to more easily find the nest again. 

The locations can be tailored to the survey area. Examples are pine, spruce, conifer, 

deciduous, ground, or not applicable (na). In Florida, we added cell phone tower and 

stadium lights. Information may be included in the comment field such as approximate 

height of nest (5 m increments), nest contents (fresh material, egg shell fragments), or 

whether the nest was seen while cruising or during a secondary search. Eagles on nests 

should be recorded with the nest record, but eagles observed separately from the nests 

should be recorded separately. Any ambiguity in recording eagles at nests should be 

discussed in the comments field of the record. 

Table 1. Variables and acceptable values for the data entry files. 

 Year 2004 Location fly

Month 4-5 (off nest) perch 

Day 1-31 na 

Pilot Consistent 

FObserver initials Location pine 

RObserver (on nest) spruce 

Plot Number conifer 

CapHist 001 deciduous 

 010 ground 

 011 na 

 01x 

 0x1 

 100 

 101 

 10x 

 110 

 111 

The Record and Transcribe programs automatically record time and location 

(latitude and longitude) from the GPS used. The time and location are recorded both in 

the track files describing the flight path and in the observation files described above for 

each observation. The flight path information is important in reconciling area 

observations with known nests and to determine how effectively the plots were searched. 

If another method of recording the transcribing is used, these should also be part of the 

data collected. Instructions on using Record and Transcribe are in BPManual.pdf 

special instructions for these surveys are included in FileInstructions.txt. 
58

Survey Notes

Observers and pilots should make a text file of notes about weather, general observations, 

problems in the protocol, and ideas how to improve the survey. Unusual seating 

positions (pilot not in the left front seat, etc.) and who is recording the data should also be 

noted. Observations for each day can be made in the same file. The file should include 

the time zone used to record the times and the datum the GPS is recording the locations. 

Recording Procedures

The front-right observer will reconcile and record observations for all three observers 

during the flight. Jack Hodges program, or a predetermined alternative, will be used to 

record and transcribe the sightings. At the beginning of the flight, give the date and 

weather. When entering and leaving each plot, say “beginning” or “ending list or area 

plot” and give the plot identification number. For contiguous plots say “leaving [list or 

area] [number] and entering [list or area] [number]” every time the plot changes (or in 

Combined plots, when the search changes from searching the habitat to checking status of 

known nests). The codes recorded will be as follows in Table 2: 

Table 2: Codes for Jack Hodges program to record sightings

Code 

ADULT 

IMMATURE 

UNKNOWN 

REPAIRED 

UNREPAIRED 

EMPTY 

DESTROYED 

NOTFOUND 

INCUBATING 

OCCUPIED 

EGGS 

EAGLET 

BEGAREA 

ENDAREA 

BEGLIST 

ENDLIST 

GPS 

COMMENT 

The first three codes are for sightings off the nest: ADULT, IMMATURE, UNKNOWN. 

The next nine are nest condition codes. REPAIRED is a nest with fresh sticks or boughs 

on top (sign of an occupied nest), UNREPAIRED if not. If the nest condition cannot be 

determined, use EMPTY. INCUBATING, OCCUPIED, EGGS, EAGLET all are codes 

of an occupied nest. Put number of adults, eggs or fledglings, nest contents not described 

by the codes, experienced observer knew location of nest, etc. in the comment field. 

BEG[LIST or AREA] and END[LIST or AREA] are recorded when entering and 

leaving each plot. The number field should have the plot number without leading zeros. 
59

That no observations were seen in a plot can be noted in the comments of an END[LIST 

or AREA] record. This will confirm that no records were missed. From the plot codes, 

ferrying and time within plots can be determined. GPS is used to record the location of a 

nest or other geographic feature. CapHist and Location are not used in GPS records. The 

comment field is used to record what location is recorded. The COMMENT record is 

used to make a note, such as fog over the coastal part of a plot. The location may or may 

not be important to the note. 

Header variables are Year, Month, Day, Pilot, FObserver, RObserver, and Plot. These 

are variables that stay constant for the number of observations and are treated differently 

than the Code, CapHist, Location, Comment variables. In the resulting dataset, the fields 

should be separated by commas. Any comments should follow after the fields. Commas 

should not be used in the comments; use slashes or semicolons instead. Acceptable 

values of the header variables are shown in Table 1 in the format used by the 

Transcribe program. 

The time will be set to the local time zone at the start of the survey, for example Eastern 

Daylight Time and noted in the survey notes. GIS locations must be recorded. Locations 

of flying eagles will be recorded after the counts have been reconciled understanding that 

they will be farther down the track from the sighting. Locations of nests should be taken 

over the nest to reconcile sightings with known nest locations. When transcribing, 

remember to save the new header variable values every time the header variables 

change. The new values will not be recorded unless you do. 

A checklist for the observers to use in the plane is included at the end of this appendix. It 

is on a separate sheet and may be laminated. 

Flight Procedures 

Seating Positions: Pilot, front-seat observer, rear-seat observer. 

Altitude and speed: Fly at 200-700 feet above ground level at around 100 miles per 

hour. Make adjustments to give the best visibility to the tandem observers when possible. 

 

Timing and sequence: Time of day should not matter unless the sun is too low and 

affects visibility. Observers should not continue when overly fatigued. Surveys should 

be run before the trees leaf out. 
60

Defining flight paths within area plots: The surveys should only include the parts of 

plots that occur within the defined survey area (i.e. within the contiguous 48 states, 

excluding areas within large bodies of water, etc.). Because eagles nest within 1 mile of 

water (i.e., coastlines, islands, inland ponds and lakes of >35 acres, and rivers >330 feet 

in width or similar definition appropriate for the geographic area), searching should be 

constrained to these locations. Flight paths should be defined on maps prior to surveys, 

preferably in consultation with an experienced eagle survey biologist. Transects will be 

flown along shorelines and interior habitats along shorelines. 

Defining flight paths within list plots: Observers should note identifying features and 

locations of known nests on maps prior to the flights. This will improve the success of 

nest searches. Record nests that are not found and ones that are destroyed. 

Defining flight paths for combined plots: Known nests in the area plots will not be 

known to the observers prior to the flight. The combined plots will be treated as area 

plots during the pre-flight planning. Then, after the plot habitat is flown, the front-seat 

observer will turn to the next map. If there are known nests, the map will contain the 

locations. The plot will then be treated as a list plot and the status of known nests will be 

obtained. If the status of the nests was obtained during the preceding area survey, then 

the nest does not need to be checked again. A non-observer will need to insert the known 

nest maps after the area plot maps for the combined plots in the order that they will be 

flown. It is important to the double observer protocol that the observers scan the habitat 

during the area plot part of the survey and not look for particular known nests. 

Shoreline transects: Surveys should be conducted first along edges of water bodies in 

plots with the right side of the plane (containing front-and and rear-seat observers) on the 

landward side of the aircraft. The pilot navigates and can act as a third observer for land 

sightings, or can observe additional land areas (e.g. islands) in the area. The plane should 

be oriented to facilitate consistent viewing regions for both observers, without tight turns 

or banking. Single observations by the pilot can be recorded separately from the tandem 

observers and entered as “1xx,” unless the pilot is counting the same field of view as the 

other front-seat observer. Areas surveyed on the shoreline pass will be one-quarter mile 

inland from edge of water, and the plane should be located close to shore. 

Interior transects: If it appears that the shoreline transect did not cover adjacent eagle 

habitat, the aircraft should turn and fly a transect with the aircraft approximately one-half 

mile inland from the shoreline after the shoreline transect is completed. The front and 

rear-seat observer will conduct the double-observer procedure in the one-quarter milewide strip that extends from the edge of the shoreline to the aircraft. The pilot will 

survey the area on the shore-ward side of the aircraft, from the midline of the aircraft 

(one-half mile from shore) to one mile from the shoreline. 

 

Islands should be surveyed by shoreline transects and if necessary (e.g., if island is >1/2 

mile wide) by interior transects. 
61

Observations: Known nests may be observed outside the plots and recorded, as may 

new nests within list plots. Information on the locations and status of these nests can be 

used to update the nest list of the next sample period but will not be used in the statistical 

estimation. These should be marked as “out of sample” in the comments. Nest searching 

in conjunction with eagle observations can be conducted, but should be limited to a single 

additional pass. During these searches, the double observer counting protocol should be 

maintained (i.e., independent counting until nest is passed). 
62

 

Eagle and Nest Observation Checklist

1. Begin plot #___ 

 2a. If an eagle off the nest 

a. Age: adult, immature, or unknown 

b. Capture history: [x, 0, 1] codes for left-front, right-front, then right-rear 

c. Distance: estimate distance in meters of a line parallel to the aircraft track 

d. Behavior: flying, perched 

e. Location: if perched on tree or ground 

 2b. If a nest 

a. Nest condition: empty, incubating, occupied, eggs, eaglets 

b. Capture history: [x, 0, 1] codes for left-front, right-front, then right-rear 

c. Behavior: on nest or perched 

e. Nest tree: pine, spruce, (generic) conifer, or deciduous 

3. Comment on nest contents including number of eagles, uncertainty about 

species’ nest, whether observed while cruising or on a secondary nest search, 

observer knowing nest location. Indicate observation off the sample plots or 

new nests in list plots 

4. End plot #___ 
63

Appendix 3 

Bald Eagle Nestlist Website 

by Mark Otto 

The Service is developing a website for the States to update their bald eagle nest list data 

and download copies of their data and other coverages needed for the bald eagle postdelisting survey. The survey team will use the nest lists to sample from and to determine 

the overall survey design. The main purpose of the website is to make it easy for the 

States to incorporate their nest list data into a national database, to insure consistency and 

integrity of the data collected from many sources, and to allow the States access to their 

own data and information they would need for the survey. The website and database 

would be the single, secure site for this data. Initially, the site will be hidden and 

protected from unauthorized users. A test version of the site was developed in July 2008. 

The site will have several secondary uses. Our Service Migratory Birds and Ecological 

Services programs may access it in the future to assist evaluations of applications for bald 

eagle permits under the Bald and Golden Eagle Protection Act. Knowing the proximity 

of bald and golden eagle nests to potential sources of disturbance will facilitate informed 

permitting decisions. Permit issuers may also be a source of information on new nests. 

Additionally, the Service’s Law Enforcement program will have access to the website in 

order to use the database information to trace any possible links to depredation on nests. 

State biologists would input data using an input form for single or small numbers of new 

nests. They could also edit past data and upload a text file or other database table. 

Uploaded data will be scanned for viruses and checked for validity. The user will 

immediately be informed of any problems with the import, so that the data can be 

corrected and imported again without undue frustration. 

The data would keep information on the locations and the status of the nests over time. 

There would be two main tables: one to record information on the nest locations, and 

another to track the sightings/status of the nest within and among breeding seasons. 

We would use the most current information to develop the survey design. Historical 

records would be used for research purposes. Since currently abandoned or destroyed 

nests would remain in the database, we would need to be diligent about recording nest 

status. 

The nest list table would include Nest ID, State, State ID, Site (e.g. Georgetown dump), 

Position (Latitude, Longitude in decimal degrees), Datum (1927, 1983, ...), Status, 

Observer, Tree or site description (spruce, cell phone tower, ground nest, ...), Position in 

structure, Comment. The sighting table would include Nest ID, year and date, status 

(adult, destroyed, deteriorated, eaglet, eggs, empty, immature, incubating, not found, 

occupied, repaired, unknown, unrepaired), territory ID if that is recorded, how the 

observation was reported, comment, and owner of the record. 

Future features might include: (1) an interactive map of nests similar to the Alaska 

website which allows information on selected nests to be displayed. 
64

(2) Displaying and printing maps of selected 10 km2

 plots with aerial photos or 

topography identifying bald eagle habitat, with or without list nests. (3) A public part of 

the website with information showing survey results and a nest map with imprecise or 

fuzzed nest locations. 

The users of the website would be the administrators, developers, bald eagle management 

team, State coordinators, State biologists, Service Migratory Birds, Ecological Services, 

and Law Enforcement programs, USGS and possibly outside researchers. All would 

access the website and database with a username and password. 

 Administrators (1 to 5 people): They would be able to add, modify permissions, 

and remove users. They could commit data to the database, edit data in the 

database, modify some web pages and code, and run audits. 

 Developers (1 to 5 people): They would create, test, and maintain the website, 

database and code. They would have the same permissions as administrators. 

(one or two people) 

 FWS Bald Eagle Management Team (10 to 15 people): They would be able to 

add, remove, and track (list) State coordinators and State biologists. We would 

need to keep good contact information for the Team and post that on the site for 

biologists and State coordinators to get help. 

 State Coordinators (50 to 100 people): They would be able to add, remove, and 

track (list) biologists within their State. We would need to keep good contact 

information for the Coordinators and post that on the site for biologists to get 

help. 
65

 State Biologists (50 to 150 people): They would be able to add, edit, and 

download information from their State. They will be able to download coverages 

and other information about the survey. 

 FWS Migratory Birds and Ecological Services (about 100 people): They 

would be able to define an area and get the nests possibly affected by a proposed 

disturbance activity. 

 FWS Law Enforcement (1 to 10 people): They will need to be able to trace 

activity by user, view when nest list records were accessed and by whom. 

For each survey period each of the States in the contiguous 48 States will be requested to 

update their list of nests to the extent that data is available. This will include adding any 

new nests that have been reported and identifying old nests that were destroyed. This 

data is already collected by many of the States. If no data is available, no changes to the 

nest list need to be made. To receive consistent information from the States, the website 

provides two ways to make changes to their nest lists: edit the nest data by nests and 

annual observations by each observation or upload the changes in a comma delimited text 

file. The biologists for each state will only be able to view and edit their own data. 
66

Bald eagle database users will log on with user name and password. The website is 

designed to avoid unintentional traffic as much as possible. 
67

The nests and annual observation on those nests can also be viewed and edited. 

Respondents may also upload or e-mail the nest list changes in a comma delimited file 

with the information described below. 
68

The database contains two main tables: one for nest location and information and another 

table for the annual observations. Some States may make multiple sightings within each 

breeding season. Only the summary records for a season will be recorded: one for the 

occupancy status, and possibly one for the productivity status if the State collects it. The 

productivity status can stand in for the occupancy if there is not an occupancy record for 

that year because a productive nest is by definition occupied. The columns for the nest 

table are: 

Column Description 

NestID Unique index among all the States. This we generate to keep track of 

nests over all States 

State Two letter state abbreviation, using the standard FIPS codes 

StateID Text or number index that the State uses for their nests. Should be 

unique within the State. This allows the State to identify nests as they do 

in their own record system. 

Lng Longitude in decimal degrees. We need the locations of the nests to 

assign nests to plots, our list cluster sampling unit. We also need the 

location to reconcile the nest with the area observations. If the do not 

have accurate locations the burden is greater on the States to assign the 

lists to plots and reconcile the area and list observations. We will display 

to five decimal places but it depends on the accuracy of the data received. 

The values will be negative to keep the values within the required -180 to 

+180 range. We do not use the recommended variable name long

because Microsoft Access confuses this with the data type long. 

Lat Latitude in decimal degrees to 5 decimal places. 

LocAcc Location accuracy: choose the number of meters where less than 10 

percent of the locations will be off by more than that distance. Usual 

GPS accuracy is 200m. Just guess at the distance. Note: National Map 

Accuracy Guidelines, rockyweb.cr.usgs.gov/nmpstds/nmas.html, use less 

than a 10 percent error or 1/30" in a 1:20,000 map or within 16.93 

meters. (Optional but we need to need to assign the nests to the correct 

10 km2

 plot, otherwise the State will need to assign the nests to plots) 

Location Description of the tree (these are not used for vegetation classification), 

site description, anything to identify the site for reconciliation. 

(Optional) 

Access Public, Tribal, Federal, State, Local managed, Private, indicate if it is 

accessible to the public. A citizen observer could legally observe the nest 

for the survey. (Optional) 

Owner ID of the person responsible for the data (Login name in the website) 

DatEntered Date the data was entered. (Entered automatically when uploaded.) 

Comment Miscellaneous but useful information (Optional). Information about 

territories may be added here. 

We keep multiple annual observations on the same nest, so we can construct the list 

frame using the annual observation information. For States that collect multiple 
69

observations in a breeding season, we can estimate the chances of missing an occupied 

nest by only visiting the nest one time. The columns for the annual observation table are: 

Column Description 

NestID Unique index among all the States (Assigned by the database) 

State Two letter state abbreviation, using the FIPS codes 

StateID Text or number index that the State uses. Should be unique within the 

state 

Status Nest status (see below) 

NEg Number of eggs or eaglets, NULL or not used if Status other than egg or 

eaglet (Optional) 

Source Public call in, State biologist, Confirmed (Optional) 

Owner ID of the person responsible for the data (Login name in the website, 

user does not enter) 

DatEntered Date the data was entered. (Entered automatically when uploaded.) 

Comment Miscellaneous but useful information (Optional) 

Nest status in the Status column of the annual observation table takes on the following 

values: 

Code Description 

destroyed Nest destroyed or gone 

eaglet 1 or more eaglet in nest 

egg 1 or more eggs in nest 

empty Empty nest, repair status unknown 

immature Immature on nest 

incubating Eagle or pair on nest displaying incubating

notfound Not found on previously known location 

occupied Occupied but not incubating 

repaired Repaired nest 

unknown Location known but status unknown 

unrepaired Unrepaired nest 

The main information we need to know to set up the list frame sampling is what the 

status of a current nest is. The important codes are nest destroyed and not found. Nests 

with other status codes make up the list frame to sample from. After a nest list is 

sampled or censused during one of the five year sampling periods starting in 2009, we 

only need to know whether a nest is occupied or not. The incubating, empty (if not able 

to ascertain repair status), repaired, and unrepaired, and unknown refine the occupied 

determination. Unknown status nests are considered unoccupied to be conservative but 

give added information on secondary analyses. If we help measure productivity from a 

sample or census of nests, we need the eggs, fledgling, and eaglet categories. We will 

use productivity data that that States are interested in collecting. Keeping and analyzing 

the productivity data is an opportunity to provide additional information to the States 
70

(and to the Service). We put it in our database to make it easy to process surveys for a 

number of States. 

The State nest lists can be updated by making the changes to the web forms above or 

uploading a table of the updates. The nest table is only updated if the data is different 

from the current information. The file would have the following information. The State, 

Owner, and DatTim (date the information was entered) will be entered automatically, 

using your username, the State that username is associated with, and the computer date 

and time. 

The location accuracy, nest access, source, and nest and annual observation table 

comments are optional fields. Almost always there are oddities about some observations 

that are not easily recorded on standard forms, but can save hours of detective work if 

they are known. It also provides a way to find out what fields should later be added to 

the formal input. We were not going to collect territory information because we cannot 

assign territories for new nests or use the information in our estimation. We will also add 

the State FIPS code, owner ID, and the data and time the owner entered the information. 

These will be tracked and added automatically using their logon information and the 

current time. We will work with the States to convert their data to a file that they can 

upload to our database. 
71

Appendix 4 

Regional Bald Eagle Monitoring Coordinators 

*For current contact information, go to http://www.fws.gov/midwest/Endangered

Fish and Wildlife Service Regions 

Region 1: Regional Coordinator – Suzanne Audet 

Suzanne Audet 

Upper Columbia Fish & Wildlife Office 

11103 E. Montgomery Drive 

Spokane, Washington 99206 

Tel: (509) 893-8002 

Fax: (509) 891-6748 

Suzanne_Audet@FWS.gov

States - CA, ID, NV, OR, WA, HI, Guam, American Samoa, Commonwealth of the 

Northern Marianas 

Region 2: Regional Coordinator – Greg Beatty 

Greg Beatty 

Arizona Ecological Services Field Office 

2321 West Royal Palm Road, Suite 103 

Phoenix, Arizona 85021 

Tel: (602) 242-0210 x 247 

Fax: (602) 242-2513

Greg_Beatty@FWS.gov

States - AZ, NM, OK, TX 

Region 3: National Coordinator – Jody Millar 

Jody Millar 

Rock Island Ecological Field Office 

1511 47th Ave. 

Moline, Illinois 61265 

Tel: (309) 757-5800 x 202 

Fax: (309) 757-5807 

Jody_Millar@FWS.gov

States - L, IN, IA, MI, MN, MO, OH, WI 

Region 4: Regional Coordinator – Candace Martino (Jacksonville) and Al 

Begazo (South Florida) 

Candace Martino 

Jacksonville Field Office 

7915 Baymeadows Way, Suite 200 

Jacksonville, Florida 32256-7517 Tel: 904 731-3142 

Fax: 904 731-3045 

Candace_Martino@FWS.gov 
72

Alfredo Begazo 

South Florida Ecological Services Office 

1339 20th Street 

Vero Beach, Florida 32960 

Tel: (772) 562-3909 

Fax: (772) 562-4288 

Alfredo_Begazo@FWS.gov

States - AL, AR, FL, GA, KY, LA, MS, NC, SC, TN, PR,VI 

Region 5: Regional Coordinator – Craig Koppie 

Craig Koppie 

Chesapeake Bay Field Office177 Admiral Cochrane Drive 

Annapolis, Maryland 21401 

Tel: (410) 573-4534 

Fax: (410) 269-0832 

Craig_Koppie@FWS.gov

Steve Mierzykowski, Environmental Contaminants Coordinator, Bald Eagle 

Monitoring Literature Database 

U.S. Fish & Wildlife Service 

1168 Main Street 

Old Town, Maine 04468 

Tel: (207) 827-5938 ext. 17 

Fax: (207) 827-6099 

Steve_Mierzykowski@fws.gov 

States - CT, DE, ME, MD, MA, NH, NJ, NY, PA, RI, VT, VA, WV, and Washington, 

D.C. 

Region 6: Regional Coordinator – Dan Mulhern 

Dan Mulhern 

Kansas Ecological Services Field Office 

2609 Anderson Avenue 

Manhattan, Kansas 66502 

Tel: (785) 539-3474 ext 109 

Fax: 785 539-8567 

Dan_Mulhern@FWS.gov

States - CO, KS, MT, ND, NE, SD, UT, WY 
73

Region 7: Regional Coordinator – Phil Schempf 

Phil Schempf 

Migratory Bird Management-Raptors 

3000 Vintage Blvd., Suite 240 

Juneau, Alaska 99801 

Tel: (907) 586-7331 or 7243 

Fax: (907) 586-7378 

Phil_Schempf@FWS.gov

State – AK 

Region 8: Regional Coordinator - Elizabeth Willy 

Elizabeth Willy 

USFWS-Klamath Falls Field Office 

1936 California Ave 

Klamath Falls, OR 97601 

Tel: (541) 885-2525 

Fax: (541) 885-7837 

Elizabeth_Willy@fws.gov 

 

States - CA, NV 

Region 9: Washington, DC Endangered Species 

Mary Klee 

USFWS, 4401 N. Fairfax Drive 

Mail stop 420 ARLSQ 

Arlington, Virginia 22203 

Tel: (703) 358-2171 

Fax: (703) 358-1735 

Mary_Klee@FWS.gov
73
74

Appendix 5 

Glossary 

Word Definition 

Allocation How much of the sample is portioned to each stratum. 

Bias The difference between the true value and the estimate. An 

estimator is biased if as you increase the sample size the estimates 

do not approach the true value. 

Cluster A convenient division of the sample into primary and secondary units, so the 

sample is chosen from the primary units then all or a sample is taken from the 

secondary units of the primary units selected. This usually increases the 

variance but makes the sample more cost effective. For example, schools are 

chosen as clusters because it is difficult to get permission to sample each 

school. Then, students only within the selected schools are sampled. 

Confidence intervals Interval that we hope the true value of the estimate falls within a given percent 

of the time. 

Detection probability The probability that an observer or observers will see the object they are 

counting. 

Estimate The value of a parameter from a statistical model determined from data. The 

formula is the estimator. 

Frame A list of all possible elements in the population. The list of all known nests or 

the list of all plots in the contiguous 48 States. We choose the sample from the 

frame. 

Independence Where one event does not give any information on the chance of another event 

occurring. For example, having more list nests does not indicate that there 

will also be more (or less) new nests found. 

Lagrange multiplier Method of optimizing a function when there are constraints, e.g., minimizing 

the variance given that only so much can be spent sampling, or minimizing the 

cost given that we obtain a precise enough estimate. 

Mean Characteristic of a population that is the sum over the number of observations; 

average. 

Normalize Make so that all the values sum to 1. It may also mean to make the values sum 

to zero and scale the values so the standard deviation sums to 1. 

Optimal The best of all possible choices. Usually choosing the parameter so the value 

of the function is maximized or minimized. 

Population The aggregate from which the sample is chosen. The target population is what 

we want to sample: active bald eagle nests. The sampled population is what 

is actually sampled: may be the active nests in our State nest lists. 

Power The chance of detecting a significant difference when a significant difference 

exists. Increasing the sample size usually increases the power. 

Precision How much estimates of the same sample size will vary. Technically it is the 
75

Word Definition 

1/Variance. As the variance of the estimate decreases, the precision increases. 

Proportional Allocation Allocating the sample among strata in proportion to the size the stratum. 

Sample The part of the population that is randomly selected and used to represent and 

measure the population. 

Significance level The percentage you will accept saying there is a true difference when it only 

occurred by chance. At a 5 percent significance level, you will get an estimate 

from a sample that is significant, not because there is a difference, but just by 

chance. The smaller you make the significance level, the greater sample size 

you are going to need to detect a significant difference. 

Standard error The standard error is the standard deviation of the estimate, not the population 

value. As the sample increases the standard error will decrease but the 

estimate of the standard error will just fluctuate less but remain around the 

same level. 

Stratum Partition of the population so that the units within each stratum are as similar 

as possible. You may stratify where sub-estimates are required. We divide 

the contiguous 48 States into strata where the density of nests differs greatly. 

Variance Measure of the scatter of the population around its mean value. The standard 

deviation is the square root of the variance. The standard error is the standard 

deviation divided by the square root of the sample size.