Nesting and Productivity of
Bald Eagles in Southeast
Alaska-1966
Fred C. Robards and James G. King
U.S. Fish and Wildlife Service, Juneau, AK
Southeast Alaska supports a dense population of Bald Eagles (Haliaeetus leucocephalus).
At the time of this writing, there is little information on the past or present status of these
birds. Bounty hunting, logging and reduction in salmon stocks may have altered the
population level from pristine times. Future development of the area may cause changes
in the population. Thus, in 1966, a study was set up to determine the present breeding
population and productivity of Bald Eagles on Admiralty Island.
Southeast Alaska consists of steep, glacier ridden, fjord cut, mainland coast fringed with
innumerable offshore mountain islands, islets and rocks. Most of the lower elevations of
this land are covered with climax rain forest of Sitka spruce (Picea sitchensis) and
western hemlock (Tsuga heterophylla). Several large river valleys have extensive
growths of cottonwood (Populus trichocarpa), a successional species. The climate is
mild and moist with annual precipitation averaging about 99 inches but varying locally
due to the effects of the high mountains. The average January temperature is 30 degrees F
and the July average is 59 degrees F. Thousands of streams and rivers provide spawning
habitat for millions of salmon and other fish. The area contains an estimated 13,000 miles
of salt water shoreline.
Admiralty Island lies in the northern portion of Southeast Alaska, is about 100 miles long
and up to 30 miles wide. Its mountains rise to an elevation of 4,000 feet. The island is
separated from the mainland by 4 to 16 miles of salt water and separated from the Pacific
Ocean by another range of islands. The spruce and hemlock forest overhangs the entire
beach line and less than 10% has been logged. The Admiralty Island study area contains
6.5% of the total coastline of Southeast Alaska.
The Chilkat Valley lies 66 miles north of Admiralty Island on the mainland and contains
extensive growths of cottonwood. The Chilkat River system provides spawning habitat
for numerous salmon runs.
Although Southeast Alaska has not been badly marred by the hand of man, it is not an
untouched ecosystem. Between 1785 and 1910 sea otters were exterminated from
Southeast Alaska. Salmon fishing began about 1878 and after about 1942 salmon stocks
began a decline and were reduced from former abundance. A small amount of logging
was done in connection with the mining, fur and salmon industries. Since 1940 the
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logging industry has been steadily increasing.
Table 1. Bald Eagle bounty data 1917 to 1952.
Period
Appropriation Bounty
Per Eagle
1917-1918
$7,500
$.50
1919-1920
5,000
.50
1921-1922
2,500
.50
1923-1914
18,000
1.00
1925-1926
20,000
1.00
1927-1928
12,500
1.00
1929-1930
10,000
1.00
1931-1932
8,000
1.00
1933-1934
10,500
1.00
1935-1936
12,000
1.00
1937-1938
15,000
1.00
1939-1940
10,000
1.00
1941-1942
none
1.00
1943-1944
none
1945-1946
1,528*
1.00
1947-1948
no bounty
1949-1950
15,000**
2.00
1951-1952
17,000
2.00
1953
no bounty***
Totals
$164,528
Eagles
Bountied
5,229
4,239
4,528
20,497
7,312
27,843
8,196
4,999
7,490
3,009
12,793
7,970
1,872
1,528
6,450
4,318
Funds
Expended
$ 2,614.50
2,119.50
2,263.50
20,497.00
7,312.00
27,843.00
8,196.00
4,999.00
7,490.00
3,009.00
12,793.00
7,970.00
1,872.00
128,273
$133,042.50
1,528.00
12,900.00
9,363.00
*Bounty Act of 1917 repealed. $1,528.00 appropriated to pay 1941-1941 claims
**Bounty Act of 1949 enacted. Bounty raised to $2.00 per eagle.
*** Bounty Act of 1949 repealed.
The Territorial Legislature established a $.50 bounty on eagles in 1917 in hopes of
protecting salmon. In 1923 the bounty was increased to $1.00. After 1941 the Legislature
failed to appropriate bounty money and the system was discarded in 1946. A new Bounty
Act was passed in 1949 paying $2.00 per eagle and remained in effect until nullified by
Federal protection in 1952.
Most of the records dealing with the eagle bounty system have been destroyed thus it is
no longer possible to know how many eagles were killed in any given year. The annual
reports of the Alaska territorial treasurer do show how many eagles were bountied for
each two year legislative period. These records show 128,273 eagles were killed and
presented for bounty from 1917 to 1952. Bald Eagle data for the treasurer's reports are
included in Table 1.
Of course, not all eagles bountied were taken from Southeast Alaska. Some of the
treasurer's reports do break down the number of bounties by judicial Division indicating
that about 80% of those bountied were from Southeast Alaska. Table 2 summarizes eagle
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bounties paid by area.
In recent years pesticides have been used in a few isolated areas of Southeast Alaska, but
we can assume this region is largely free from this menace.
Table 2. Bald Eagles Bountied in Judicial Divisions.
Period of
Record
1917-18
Southeast
1st Judicial
Division
3,958
Northwest
2nd Judicial
Division
0
South/Southwest
3rd Judicial
Division
1,270
Interior
4th Judicial
Division
1
1921-22
1923-24
1925-26
1939-40
1941-42
Totals
2,023
11,475
7,008
5,551
1,110
31,125
0
2
1
3
0
6
240
3,195
299
2,408
762
8,174
1
0
3
8
0
13
Objectives:
The overall objectives of this study were to determine the status and productivity of Bald
Eagles on relatively undisturbed areas in Southeast Alaska.
We intended to develop survey methods that could be used in other parts of Alaska and
also that could be repeated from time to time to determine any change in status or
productivity at some time in the future.
Methods:
Admiralty Island was selected as the primary study area as it represents a large relatively
undisturbed block of Bald Eagle habitat. The shoreline was measured on one inch to the
mile U.S.G.S. maps and divided into 86 plots of ten miles each. Islets immediately
adjacent to the main island were included in the measurement. Ten plots were picked at
random for intensive study. Observations were made from a four place Cessna 180 float
plane, from a three place helicopter, from a 50 foot motor vessel and from a skiff with an
outboard motor.
Most of the nests were located with the airplane using two or three observers. Repeated
passes, sometimes as many as ten, would be made along the study area. All nests located
were marked on one inch to the mile maps and other data were recorded (Table 3). The
initial survey was made at a time when the snow had fallen from the branches of the trees
but remained piled in nests. Subsequent searches were made after the presence of eagles
in or near nests helped attract the observers' attention. A search was also made from the
deck of the vessel and from the skiff. A few additional nests were located by this means.
The searchers would continue surveys until repeated effort produced no new results.
Nests were frequently difficult to see and obviously some nests must have been missed in
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spite of our best efforts.
The airplane was of no use in counting eggs or young, but the helicopter proved most
effective. Eagles could be flushed from the nests successfully and they usually got well
out of the way although returned to the nest almost immediately when the helicopter
moved away. Two eagles showed some hostility toward the helicopter but the pilot
maintained a position above any nearby birds where he could frustrate an intended
attack with the blast of the prop wash.
Observations from the water, in spite of the opportunity to use binoculars, proved largely
ineffective for locating nests. All observations in this report were made by the authors
and Keith Banning and Karl Alstead of the Bureau of Sport Fisheries and Wildlife in
Juneau.
Results:
Nest Location
Nests within the study area were all located in trees. A single ground nest, an active nest,
was located on a treeless grass covered islet four miles offshore from Admiralty Island.
This nest type is limited in this area, but is more common in treeless areas of western
Alaska.
On Admiralty Island the entire beach fringe is covered with spruce-hemlock forests.
Probably due to their larger, more suitable limb structure, 90% of the nests are located in
spruce trees. Nest trees may be either alive or dead, but are always of the larger size in
the area. Nests may be located at the extreme top of a tree where something has broken
the tip above a whorl of branches. Nests may also be located in crotches or on clusters of
branches below the top of the tree but always in the top third of the tree. Nests below the
top of the growing tree are obviously the most difficult to see.
In the Chilkat Valley most nests are located in crotches of large cottonwood trees which
fringe the channels of the river. These nests are easy to see before the leaves come out in
the spring.
Most of the nests are located in trees near the water's edge, but some may be behind the
beach fringe and up to 200 yards from the water. All nests are located in such a way that
there is a clear flight path to a near point on the beach or river with no obstructions the
bird would have to fly up over.
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Table 3. Eagle data card.
Eagle Data Card - Bald or Golden
Observer’s Name:
Address:
Transportation Used:
Date:
Geographic Location of Nest:
Usable Landmark to Relocate Nest:
Nesting Site
Merchantable Timber:
Tree Species:
Shrub Species:
Cliff or Other Location, Describe:
Height From Ground:
Height From See Level:
Nest Activity
No Activity:
Adults in Locality:
Active Nest Building:
Incubating Eggs:
Brooding Young:
Eggs in Neat, Number:
Young in Nest, Number:
Date of Hatch:
Date Young Fledged:
Mortality Observed:
Cause of Mortality:
Complete a data card for each observation of change
in nest status. Use reverse side for supplemental data
or to add notes on above.
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Prevailing weather, soil type and other factors affect the overall height of tree growth and
in some areas the timber is markedly stunted. Bald Eagles nest in the stunted timber at
about the same rate as in the full growth stands, but always in the larger trees of the stand.
Bald Eagle nest tree sign used to mark nest trees under the cooperative agreement
between the U.S. Fish and Wildlife Service and the U.S. Forest Service. Photo by
USFWS.
Nest location on the Admiralty Island study area shows some selectivity toward certain
types of beach frontage. The greatest density was found in areas fronting a wide expanse
of open water. Second preference appeared to be small islands. Small confined bays seem
to be less attractive and bays that are ice covered into the nesting season are not used at
all (Table 4). Beach types were classified by one-half mile divisions for the entire study
area. We found that the ten primary study plots were quite representative of the entire
area. Beaches exposed to an open expanse of salt water may provide the best source of
food.
Nests were fairly uniformly distributed (Table 4) except in the iced-in bays, in the several
small patches of second growth timber where suitable trees were not available and in a
few small areas adjacent to settlements where human harassment may be a factor.
Exposure to the sun, locations of salmon streams and prevailing winds do not seem to
influence nest site selection.
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Nest Construction
Nest material can be drift picked from beaches or branches collected from dead trees and
bushes. The nest platform is composed of sticks of all sizes up to four feet in length and
two inches in diameter. The nest is lined with grass, twigs, seaweed and other debris.
Many of the nests appear to have been in use for many years. Some nests, evidently not
recently used, support a heavy growth of moss and grass.
Nest Density
The ten mile plot size proved large enough to contain a relatively representative amount
of beach front types as described in the preceding section. Table 5 shows the density of
nests per plot to be remarkably uniform. The Admiralty Island, Douglas Island and Auke
Bay plots contain ten miles of beach. The Chilkat River plots contain ten miles of river
frontage each.
Table 4. Relation of active nests to beach front type on Admiralty Island.
Total
Habitat Study Study
Nest
Total
Indicated
Plot Active
Plot by
Incidence Mile
Type
Nests Mileage Type Mile by Type
Active
Nests for
Admiralty Is.
Open Coast
Protected Coast
23
6
31.0
15.5
0.74
0.39
287
80
212
31
Ice Free Bay
11
24.5
0.45
289
130
Iced-In Bay
Islands & Islets
0
13
6.5
22.5
0
0.58
85
119
0
69
Total
53
100.0
0.54
860
442
The function of the large number of inactive nests could not be determine from a one year
study, but only a few a them had been abandoned long enough to support a dense growth
of grass and other vegetation. The direct distance between nests on the plots was
measured with calipers on the map. Table 6 shows the distance between active nests,
between inactive nests and between all nests regardless of activity on the Admiralty
Island and Chilkat River plots. It appears that these eagles do not nest closer than 700
yards to each other and this suggests a territory size.
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Table 5. Comparison, nesting density, Admiralty Island, Douglas Island, Auke Bay and
Chilkat River areas.
Study Area
Admiralty Is.
Plot
Total
Number Nests
7
19
21
24
27
36
45
53
54
82
Totals
Douglas Is.
Auke Bay
Totals
Chilkat River
1A
2A
3A
1
2
3
4
5
6
Totals
Total for all Plots 217
Active
Nests
Average Active
Nests Per Mile
Percent of
Total Active
Nests
14
13
10
14
11
14
14
16
11
16
133
5
7
5
5
5
5
6
6
4
5
53
0.5
0.7
0.5
0.5
0.5
0.5
0.6
0.6
0.4
0.5
0.5
40%
8
8
12
28
5
4
7
16
.5
.4
.7
.5
57%
7
12
9
6
6
12
52
93
5
6
4
3
2
4
24
0.5
.5
.6
.4
.3
.2
.4
.4
43%
46%
Nesting Period
During most of the year eagles are not observed using nest platforms for perching. Early
in April eagles are seen perched in nests indicating the rehabilitation of nests has begun.
The helicopter was used to check 72 nests on and adjacent to the Admiralty Island study
area. During 1966, all birds with eggs were incubating on or before May 9, all eggs had
hatched by June 7 and all young were well feathered and nearly ready to fly by July 7. A
variation in size of nestlings was observed on June 7, indicating hatching dates may vary
as much as two weeks.
Editors' Note: More recent studies have identified the inactive nests as old nests or nests
not otherwise used by the eagles maintaining the territory. These nests may be used in
subsequent years.
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Table 6. Distance between nests in miles in SE Alaska.
Admiralty Island
Number of Nests
43.00 68.00 119.00
Average Distance
1.12
.85
.55
Closest Nests
Farthest Nests
Chilkat Valley
Number of Nests
Average Distance
Closest Nests
Farthest Nests
.40
4.00
.10 .10
2.50 4.00
18.00
1.18
.60
2.00
24.00 48.00
1.15 .76
.50 .20
2.60 1.70
Productivity
Table 7 summarizes data for the 72 nests checked by helicopter. The clutch size was from
1 to 3 eggs with an average of 1.96 eggs per nest. An 82% hatching success and a 72%
survival rate to fledgling was determined.
Table 7. Productivity and survival rate of 72 SE Alaska nests.
No. In Nest
Eggs 5/9/66
Downy Young 6/7/66 Preflight Nestlings 7/7/66
0
1
2
3
Total
0 nests
6 nests
63 nests
3 nests
141 eggs
4 nests
20 nests
48 nests
0 nests
116 downy young
9 nests
24 nests
39 nests
0 nests
2 feathered nestlings
Survival rate in 72 SE Alaska nests
Egg Survey 5/9/66 Downy Young Survey 6/7/66 Preflight Nestlings 7/7/66
Number 141 eggs
116 eaglets
102 eaglets
Average 1.96 per nest
Survival 100%
1.61 per nest
82%
1.42 per nest
72%
The 1966 production data from the 72 nests checked by helicopter was combined with
data on active nests from the ten Admiralty Island study plots. This indicates that the
entire study area may have produced 648 ±69 fledgling eaglets (Table 8).
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Table 8. Indicated bald eagle production on Admiralty Island.
Eggs (May) Downy
Pre-flight
Young (June) Nestlings
(July)
Minimum
Nests
408
800
657
579
Maximum
Nests
504
988
811
716
Average
894 ±94
734 ±77
648 ±69
Conclusions
The objectives of the study were met. The researchers involved with this study did not
expect eagles nests to be so numerous or to have such an even distribution. Of particular
interest is the indication that the marine environment is the primary source for food for
nestling Bald Eagles and the association to salt water appears to effect nestling densities
more than any other factor. Only the very largest of the salmon streams, such as the
Chilkat River, produce enough food to effect nesting distribution.
This Bald Eagle is watching for salmon along the Chilkat River.
Photo by Bob Armstrong.
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The study method used proved to be satisfactory and might be appropriate for use in
other areas. For instance, with this strip plot census technique, it would be possible to
sample all of Southeast Alaska and develop statistically reliable figures for not only eagle
production, but for habitat types, iced-in bays, etc. Money and time are the only limiting
factors.
Editors' Note: This paper has been cited numerous times since 1966 yet it remained in
the gray literature and difficult to obtain. It describes the earliest work for assessing Bald
Eagle nesting and productivity in Southeast Alaska using methodology that continues to
be the basis for collecting these data today. For these reasons the editors decided to
include this important historical work in Bald Eagles of Alaska.
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