BlM/AK/OF-83/05 BlM-Alaska Open File Report 5 

June 1983 

Results of the 1.982 Bald Eagle 

Nest Survey in the Glennallen 

Resource Area 

by	 Laurence C. Byrne 

Julie S. Henderson 

Michael W. Small 

Bureau of Land Management 

Alaska 
OPEN FILE REPORTS 

The category of "Open File Report" is used by BUt-Alaska to identify 

the results of inventories or other investigations that are made 

available to the public outside the formal B~~-Alaska technical 

publication series. These reports include preliminary or incomplete 

data that are not published and distributed in quantity but that are 

available for public inspection at BLM offices in Alaska, the USDI 

Resources Library in Anchorage, and the various libraries of the 

University of Alaska. 

Copies of open file reports are also available for inspection at the 

USDI Natural Resources Library in Washington, D.C. and the BL~ Denver 

Service Center library. 

At the time this report was prepared Laurence C. Byrne and Julie S. 

Henderson were employed as seasonal wildlife biologists on the Glennallen 

Resource Area. Michael W. Small is a natural resource specialist with 

the Glennallen Resource Area of the Bureau of Land Management's Anchorage 

District. 
Study Area 

The study area (Figure 1) includes both the Denali block (4.5 

million acres) and the Tieke1 block (507,000 acres) of BL.~ administered 

land. Included within the Denali block are the Gu1kana Wildlife 

Habitat Area (WHA) (1.1 million acres) (Appendix 1) and the Delta WHA 

(72,000 acres) (Appendix 2). These two areas were inventoried for 

bald eagle nests in the summer of 1981. Descriptions of the- study 

areas can be found on the write-up of the 1981 BL~ survey. 

The 1982 survey was expanded to include suitable bald eagle 

habitat in the remainder of the Denali block (Appendix 3). This 

consisted of: the Upper Susitna River (both the east and west forks) 

above the Oshetna River; Valdez Creek; the Maclaren River; Clearwater 

Creek; the Nenana River (above Wells Creek); Brushkana Creek; Butte 

Creek; Wickersham Creek; the Oshetna River; Sanona Creek, and the 

upper reaches of the Tyone Creek~ The surveyed area is fairly. 

mountainous; elevations of the valley floors range from 2,500 feet to 

5,.000 feet above sea level (a.s.l.). At lower elevations, continuous 

stands of lowland spruce-hardwood forests are common. Towards the 

headwaters of the streams, suitable bald eagle habitat is found in 

upland spruce-hardwood stands that become less continuous and more 

isolated as elevation increases. 

The survey was also expanded to include the Tieke1 block (Appendix 

4), where it was limited to channels cut by streams running through 

the Chugach Mountains, which dominate ,the area. These streams were 

the Tonsina River, the Little- Tonsina River, the Tiekel River, Bernard 

Creek, and Dust Creek. Upland spruce-hardwood forests occur along 

most of the s~ctions of the rivers which were surveyed. White spruce 

(Picea glauca), black cottonwood (Populus trichocarpa), and balsam 

poplar (Populus ba1samnifera) were the common species. Elevations 

range from 1,400 feet to 2,700 feet. 

Methods 

The methods used for the 1982 survey were the same as those for 

the 1981 survey. A description of procedures and equipment used can 

be found in the 1981 BL~ Bald Eagle Nest Survey report. In 1982, 14.9 

hours of flight time (seven flights) were devoted to the nest survey. 

The surveys in the Gu1kana River and the Delta River WHA' s (4.4 hours 

(~NO flights) and 1.6 hours (one flight), respectively) were limited 

to checking the status (active, inactive, not found) ~f nests located 

in the 1981 survey. New nests were not searched for, but if encountered, 

they were recorded. Six and one-half hours (three flights) were 

devoted to surveying the remainder of the Denali block. Two and 

three-tenths hours (one flight) were needed to survey the Tiekel 

block. All but one flight were conducted in an l8-day period from 7 

June to 25 June. Sanona Creek, Tyone Creek, and the Oshet:na River 

1 
- - - - - - - - - - - - - -

- - - - -

- - - - - - - - - - - - - - - -

- - - - - - - - - - - -

-------~<----------

( 

. 

... /J co •• "'41 ., ~~

~'J/lUJ:e 1. 

DerlaH Block 

Study area shcMng the IlensU Block 

ttrld TI eke I Block of 81H orln/nJstered Ittrld. :til, 

• 
were surveyed on 13 AugUSt for presence of nests only. 

In addition, three nest trees were measured along the lower 

Gulkana River from Sourdough to the Richardson Highway bridge (Henderson, 

Byrne, Ziegler, 23 June). The diameter at breast height (dbh) and 

height of the nest trees and distance to water were measured; habitat 

description, nest visibility and accessibility, and observations of 

active nests were recorded. The upper Gulkana River from Paxson Lake 

to Sourdough was floated (Henderson, Byrne, Recreation Crew, 1-8 

July). Observations of active nests were recorded. 

No ground survey of nests in the expanded areas was conducted 

because of their inaccessibility. 

Result:.s 

Gulkana WHA and Delt:.a WHA: 

During t:.he 1981 BLM Bald Eagle Survey, 49 nest:.s were found in t:.he 

Gulkana and Delt:.a Wildlife Habit:.at Areas. When these areas were 

resurveyed in 1982, 38 of the 49 nests were relocated. The single 

ground nest was essentially gone by autumn 1981 and seven trees nests 

probably blew down sometime during the past year. Three of the nests 

not relocat:.ed may still exist. Two nest locations in the lakes region 

may have been mismapped, and one nest in a poplar tree may have been 

present but not visible because of the screening effect of the poplar 

leaves. 

In addition. five new nests were found. ra~s~ng the total nests 

to 43 (Gulkana WHA-39, Delta IfHA-4). All calculations include only 

the nests seen in 1982. 

Nest Activity 

Nests were determined to be active if an adult eagle was present 

on the nest. or if eggs or young were seen in the nest during the 

aerial survey. Since eagles may initiate nesting later than the 

survey date (Bent 1937 in Snow 1973), defend inactive nests (Ro1ands 

and Hodges 1976). or simply perch on an inactive nest. activity status 

recorded for some nests may be wrong. For example, no eagle was seen 

on Paxson Lake nest #5 on 2 June, 1982, the official survey date. One 

week lat:er, on an incidental flight. an adult: eagle was seen on the 

nest, but to be consistent, the nest was still considered inactive. 

In addition, one nest (Paxson Lake #4) known to be active in mid-May 

but abandoned by the survey date was also considered inactive. 

3 
--------------------

, , . . 

.......
 

Table 1 Change in use of thirty-eight nests present in both 1981 and 1982. 

(Percent activity is shown in parentheses) 

-----~---------~lta-­

w"HA WHA

Paxon Gulka:na West and Lakes Total Delta 

Lake tA.ainstem Middle Fork Area WHA River 

Gu1ka:na 

~~~pre~t~--------------------­

1981 and 1982 5 10 9 10 34 4 

B# nests activein- - - - - - -.- - - - - - - - - - - - -­

- 1981 

(%=B/A) 3(60%) 6(60%) 5(56%) 5(50%) 19(56%) 1(25%) 

c Tnestsaetive in --- - - - - - - - - - - - - - - - - -­

- 1982· 

(%=(;/A) 1 (20%) 7(70%) 5 (56%) 5 (50%) 18 (53%) 1 (25%) 

D#n~~civein--------------------­

- 1981 and 1982 

(%-D/A) 1(20%) 6(60%) 4(44%) 4(44%) 15(44%) 1(25%) 

E--------r;--------------------- iF nests active in 81
 

inactive in t 82


(E=B-D) 2 0 1 1 4 0 

F#~s~~t~e~-------------------­

- I 81 active in 182 

(F=C-D) 0 1 1 1 3 0 

nr~~o~~---------------------­

nests
 

(G=D/B) 33% 100% 80% 80% 79% 100%
 

PUf:5. considered inactive. may have been active. If so. t:.."rl.s figure 1M:lU1d be 67%. 

4
 
In both 1981 and 1982, 49% of the nests in the Gulkana and Delta 

WHAs were active. This percentage indicates an overall level of 

activity; it does not mean that the same nests were active in 1981 and 

1982, as eleven nests were not relocated, five new nests were found, 

and the active status of seven nests changed from 1981 to 1982. 

Thirty-eight nests were present both years; four in the Delta WHA 

and 34 in the Gulkana w1ffA. The single active nest in the Delta TIHA in 

1981 was again active in 1982, indicating 100% reuse of active nests 

in this area. 

Of the 34 nests in the Gulkana WHA, 19 were active in 1981. 

Fifteen of these 19 active nests were again active in 1982, indicating 

a high reuse (i9%) of nests. Only four active nests became inactive, 

and three inactive nests became active. These changes in activity 

status were spread across the Gulkana WHA (Table 1), and were not 

concentrated in any single area. 

The high percentage of nest reuse, and the same overall level of 

activity in the two WHAs suggest that the nesting situation is stable 

for the one-year period. No widespread use of alternative nest sites 

is apparent. However, nesting activity does not indicate nest success. 

Byrne et al (1982) compared activity status of nests in motorized 

and non-motorized sections of the mainstem Gulkana River. Activity of 

nests (83%) remains the same in 1982 as it was in 1981 for the nonmotorized section. In the section used by both rafters and fishermen 

in motorboats, one nest inactive in 1981 was active in 1982 and another 

inactive nest was found. Therefore, nest activity in this section 

increased from 20% to 33%, still much lower than in the undisturbed 

area. High nest density (.SO/mile) suggests that the area is good 

eagle habitat. There are several possible explanations for the large 

number of inactive nests. Several eagle pairs may have nested there 

in the past, but have been displaced from the area by increasing human 

disturbance. A second possibility is that a single eagle pair nested 

in the area, but built new nests in different sites as a response to 

human activity. Variable food supply and weather conditions are two 

factors which may also help explain the situation. 

Nest Distribution and Density 

No new nests were found on the Delta River. One nest or nest 

tree had blown down, and the ground nest no longer exists. The loss 

of two nests reduces nest density in this area from .12/mile to .08/mile. 

Active nest density remains at .02 active nests/mile, a low for the 

two WHAs. Nest densities for the Gulkana and Delta WHAs are found in 

Table 2. 
- -- - - - - -- -- -- -- - - -- - -- -- - - - - -- -- -- - - - -

- - -- - - - - - - - - - - - -- - - -- - - - - - - - - - - - - - - - - - -

<. f •• 

Table Nest density along streams in Bald Eagle nesting survey area 1982. 

Area 

Miles Habitat 

St.rrVeyed Nests/mile 

Active nest/ 

miles 

Gulkana.-mainstem 

Paxson Lake to Sourdough 45 .24 .16 

Qillc:ana - West Fork 95 .08 .04 

Gulkana - Middle Fork 30 .13 .03 

Delta 49.08 . 02 

Susitna 65 . 09 . 05 

Nenana 

C1eaxwater 

Tonsina 

Lawer Gulkana. 

Sourdough to Gulkana. bridge 

Oshetna* 

S~*

Tyone* 

28 

19 

7 

34 

9 

18 

15 

.09 

.il 

.14 

.09 

.11 

.11 

.13 

.05 

.11 

.14 

.03 

Total 414(390**) .15 . 07 

Lake Area 

Mile2Habitat 

351 

Nests/mile2 

.03 

Active nests/mile2 

.02 

*Active/inactive status of nests was not detemined
 

** Mileage of streams St.rrVeyed on 1Nhich status of nescs was determined.
 

6 
In t:heGulkana 1;JHA. deusit.y ',rar.ie.s with area surveyed. One nest. 

in t.'he Ma.i.ns.t:em below the confluence with the West Fork, blew down, 

and one deteriorat:ed nest in t:he same area was found. Nest density 

remains at ~24 nest:slmile. and act:ive nest density increased from 

.B/mile t:o .16/mile. 

Three neazs on the West Fork blew down, reducing nest density 

fram .ll/mile t:o •as/mile. Active nest density decreased from .OS/mile 

to .04/mile because one of the down nests was active in 1981. On tile 

Middle Fork. the one active and three inact:ive nests were che same as 

in 1981. 

In che Lakes area, two nests were determined down and three were 

not relocated. One nest was found on Fish Lake, but overall nest 

density decreased f1:am •04 nests/ sq. mile to •03/sq. mile, and act:ive 

nest density remained at: .02/sq/mile. 

The survey was expanded 1:0 include the Susitna Rive1: d1:ainage. A 

16.9 mile sect:ion of the Susitna River is che western boundary of the 

Gulkana WHA, and two nest:s were found in t:his section. Calculations 

on density are included with the ot:her Susitna River nests in the next 

section of, this report:. 

Informat:ion 1:eco1:ded f01: nest crees included tree species, height, 

and distance to water and. elevation. Since the area sU1:'Veyed is 

essent.ially the same as in 1981, the only changes in this information 

result f1:om finding five nests and not relocating eleven nests. It is 

likely the average nest. location for the Gulkana and Delta WHAs is 

similar to the one described for 1981 (By1:ne et al 1982). New. 

information has been incorporated into calculations for the enti1:e 

st.udy area. including the expanded survey, and can be found under the 

section entitled "Total Study Area." 

ExPanded Study Area 

Eight.een bald eagle nest.s are located outside of the Gulkana and 

Delta WHA&. Six of these nests are on non-BL~-administ.ered land just 

outside the WHA boundary. They are included in this summary to increase 

the sample size. Management recommendat.ions will not include these 

nest.s. Two of the six nest.s were active (33% active) in 1982. This 

is the same as the 1981 figure for these nests, however, the same 

nests were not necessarily active in bot.h years. The nest. on Horseshoe 

Lake was active in 1981 but not in 1982. The nest on Susitna Lake was 

inactive in 1981 and active in 1982. Gulkana-14, on the lower Gulkana 

River, was active in both years. 
For these six nests, the average height of the nest tree was 53.3 

feet. The average distance from the nest tree to water was 124 feet. 

Elevation averaged 1967 feet asl. All nests were in white spruce 

trees. 

Only one nest (Tonsina-l) was located in the Tiekel Block. This 

nest was active in 1982. It is likely that another nest (or nests) 

exists in the area, but was not located during our survey. Other 

nests have been documented to exist in the area in the past. In May 

1981, a downed cottonwood tree with a bald eagle nest in its crown was 

observed on the bank of the Tiekel River near milepost 52 of the 

Richardson Highway. This nest, the Tonsina nest, and an additional 

nest along the Little Tonsina River were all preViously documented and 

mapped (Joint State/Federal Fish and Wildlife AdVisory Team, 1976). 

An adult eagle was sighted on the Little Tonsina River near the location 

plotted as a nest site in 1976. No nest was observed. It is assumed 

that this nest is down. Large cottonwood trees exist along much of 

the upper Tiekel River. It is likely that a nest (or nests) exists 

along this river, but was not visible because of the leaves shielding 

it from view. 

Eleven nests were observed in the Denali block, outside of the 

WHAs. The active/inactive status of five of these nests (Oshetna 1, 

Sanona r-l and 2, Tyone r-l and 2) could not be determined because of 

the late timing of the survey (13 Au~ust 1982). Mature golden eagles 

were sitting in two of these nests. It is not known if golden eagles 

nested at these sites or were merely perched there. Both nests were 

located in the top of spruce trees (species undetermined) and appeared 

similar in shape and material to bald eagle nests. Mature bald eagles 

were observed near another two nests. No immature eagles of either 

species were observed near any of these nests. 

The active/inactive status of the remaining six nests was 

determined. Four of these nests were located along the Susitna River, 

two of which were active (50% active). Two other nests were found 

along the Susitna River within the Gulkana WHA and one of these was 

active. For the entire stretch of the Susitna River which was surveyed, 

50% (3 of 6) of the nests were active. 

There was also an active nest on Clearwater Creek and an inactive 

nest on the Nenana River. 

For the entire expanded study area, the status of 13 of 18 nests 

was determined. Of these 13 nests, six were active (46% active). 

This compares with 49% active nests for the combined Gulkana and Delta 

WHAs in 1982. 

The average height of all nest trees was 44.1 feet. The average
 

distance from nest tree to water was 75.8 feet. The average elevation
 
Figure 1. 

24
 

-

22


20
 

18
 

16
 

iF 

14
 

nest:s U
 

10
 

8
 

6
 

4
 

2
 

Number of act:ive and :ina.ct:ive nest:s in trees of different: 

height: classes. 

Bll=tiveNest:s 

Act:ive 

I 

20 30 40 50 60 70
 

nest:-tree height
 

-9 
at which nests were found was 2,375 feet asl. Five of the nests were 

built in white spruce trees, cwo in black spruce, four in spruce trees 

of undetermined species, and one in a cottonwood. 

Densities of nests along streams within the expanded study area 

are presented in Table 2. Densities are in general agreement with 

those found for streams within the Gulkana and Delta w~s, except 

along the mainstem of the Gulkana River which has the highest density 

within the study area. The high density of active nests along 

Clearwater Creek and the Tonsina River can be attributed to the one 

active nest found along the short section surveyed along each stream. 

Only the Susitna River had more than one documented active nest. All 

three active nests along the Susitna occurred within a 29.5 mile 

stretch of the river. The shortest distance becween active nests was 

eight miles (Susitna 6 to Susitna 4). 

Total Studv Area 

Data for the entire study area was combined to calculate average 

nest tree heights, distance of nests to water, and nest tree species. 

Results were separated for active and inactive nests; therefore, 

calculations do not include the five nests surveyed 13 August 1982, 

because act~vity status was unknown. 

The majority of nests (84%) were in white spruce trees, with 

another 5% of nests in spruce trees of undetermined species (white or 

black). Only 11% of the nests were in cottonwood trees. There was 

little or no difference in nest activity status becween tree species. 

Nest tree heights ranged from 30 to 65 feet, with average tree 

height being 46.6 feet. Most active nests (59%) o~curred in trees 

be~Neen 41 and 50 feet; inactive nests occurred more often in slightly 

shorter trees (31 to 40 feet-38%, 41 to SO feet-28%). This information 

is shown in Figure 1. When in spruce trees, a nest was usually in the 

broken or dead top of the tree. Therefore, nest tree height approximates 

nest height above ground. 

Only 12% of nest trees were leaning at an angle greater than 10 

degrees. Nest trees were often the largest and/or stoutest trees in 

the stand. Few trees were dead below nest level. 

Most nest trees (66%) were within 100 feet of water, though 25% 

of the nest trees were greater than 200 feet from water. Only 4% of 

the nest trees were further than 300 feet from water. No apparent 

relationship exists between activity of the nests and proximity to 

water. 

10 
Elevations of eagle habitat surveyed ranged from 1,400 feet 

a.s.l. (Tonsina River) to 2,800 feet a.s.l. (Delta River, Maclaren 

River, Sanona Creek, Clearwater Creek. Tyone Creek). Eagle nests were 

found between elevations of 1.500 feet and 2,800 feet. Areas surveyed 

which appeared to be reasonable eagle habitat such as Brushkana Creek. 

Butte Creek, Dust Creek, Bernard Creek, and Monahan Creek, are at the 

upper extremes of these elevations ranging between 2,600--3,000 a.s.l. 

Elevations higher than 2,800 feet in this study area may suggest 

marginal eagle habitat. 

Average elevations for active and inactive nests, by area, are 

shown in Table 3. The highest elevation of an active eagle nest was 

2,700 feet; this nest was also the only active nest in the Delta WHA. 

This area has the highest average elevation for eagle nests, and the 

expanded study area has the lowest average elevation of eagle nests. 

Table 3 Average elevations above sea level of eagle nest trees 

Active Inactive Total 

feet IF feet iF feet IF 

Gulkana WHA 2271 20 2339 19 2304 31 

Delta WHA 2700 1 2717 3 2712 4 

Expanded area 2154 6 2121 7 2136 13 

Total Study area 2261 27 2326 29 2295 56* 

*doesn't include 5 nests of unknown activity status 

Recommendations 

The bald eagle population in the WHAs appears to be stable with 

respect to the situation in 1981. Forty-nine percent of the nests 

were active in both years. This is comparable to the 46% active nests 

in the study area outside the WHAs. 

The area along the Gulkana River from the West Fork down to 

Sourdough showed substantially less nesting activity (20% active nests 

in 1981, 33% in 1982) than the upper Gulkana (83% active in both 

years). The lower stretch of the river is highly productive, as 

evidenced by the large number of fishermen attracted to the king 
salmon run each year. Even with the heavy use by fishermen. the 

establishment of fish camps and the associated disturbance of motorized 

boats. there were rwo active nests in 1981. This situation should be 

further monitored with future surTeys to determine if nesting activity 

is indeed increasing or if the increase in activity is just a minor 

fluctuation in the long-term average. 

Color-banding mature eagles at nest sites would aid in monitoring 

bird displacement and nest fidelity. A banding program would help 

determine if only older birds. conditioned to high levels of disturbance, 

are nesting along this stretch of the river. If that is the case, 

nesting activity will decrease as older birds die out and younger 

birds are displaced from the area. 

Several points became apparent while conducting this survey. It 

is recommended that these points be addressed in the future to make 

the information gathered in the survey more uniform. complete, and 

reliable. 

1. The survey was conducted tuo late (mid-June) to pick up some 

nests built in poplar or cottonwood trees. This was probably the case 

for a nest in a poplar tree on Fish Lake (Fish Lake-2). This nest was 

active in 1981, but was not relocated in 1982. It is likely that bald 

eagles nest along the Iiekel River in cottonwoods. That a nest was 

not found along that river could be due to shielding by deciduous 

leaves at the time of the survey. Flights before leaf-out (mid-May) 

would help locate these nests. 

2. The method of determining the active/inactive status of a 

nest was based on a single flight. The presence of a mature eagle on 

the nest was taken to indicate an active nest. Reproductive activity 

(e.g. incubation), eggs, or young were not necessarily observed. 

Another flight later in t~e season (late June or early July) would 

prOVide more accurate information about whether a nest was used to 

produce young. ~umber of young and success of the nest could be 

determined by a late surley. 

3. The WHAs were initially surveyed in 1981. In 1982, only 

known nest locations were resurveyed to determine nest status; the 

areas were not surveyed for new or preViously overlooked nests. It is 

apparent from the 1982 survey that winters can take a heavy toll on 

nests. Eleven of the nests in the WHAs were not relocated in the 1982 

survey. It is important to look for new nests, as they indicate the 

attractiveness and productivity of an area to bald eagles. At least 

once every five years the entire study area should be resurveyed for 

new nests. 

12 
Byr.ne, L. c., D. W. Daum, M.. W. Small, andJ. S. Henderson 1982. 

Results of the 1981 BLM Bald. Eagle (HaJ iaeetus leuc:::ocePhalus 

alaskanus) Nest Suxvey COnducted in the Gulkana River ana Delta 

River Wildlife Habitat Areas.