First Symposium on Steller’s and White-tailed Sea Eagles in East Asia pp. 17-28, 2000
UETA, M. & MCGRADY, M.J. (eds) Wild Bird Society of Japan, Tokyo Japan

Postnatal development of Steller’s Sea Eagles sexing and aging techniques
Vladimir B. Masterov
Department of Vertebrate Zoology, Biological Faculty of the Moscow State University,
119899 Moscow, Russia. e-mail: eagle@soil.msu.ru

Abstract. To evaluate the impact of varying feeding conditions on reproductive success of Steller’s
Sea Eagle Haliaeetus pelagicus, I studied development of 71 eaglets during seven breeding seasons.
Significant differences between the sexes in body development are manifested at 45-50 days.
According to discriminant analysis of a complex of eaglet morphometric characteristics, females
comprised 45.07% of the nestlings studied. Rate of development and the number of eaglets produced
were significantly correlated with hatching date. Eaglets hatched out early grew significantly slower
than those hatched later. The number of eaglets per brood (soon after hatch), correlated negatively withthe time of egg laying. Females hatched significantly earlier than males in nests with two eaglets ofdifferent sexes. Older siblings were usually dominant over younger ones during the first month after
hatching due to difference in size. The rate of growth of younger siblings decreased significantly (P =0.05) in comparison with older siblings in conditions of low food supply. Worsening feeding
conditions are probably caused by changes in the hydrologic regime of water bodies upon whicheagles nest, and explains the relation between water regime and growth rate of eaglets. Growth rate
decreases when water level fluctuates far enough from an average optimal value. Declines in foodsupply related to water level may aggravate age-related differences in size, promote fratricide and leadto decreased breeding success. In years with average water level breeding success was significantly
higher.

INTRODUCTION
The nesting period is the most important phase of a bird’s annual cycle. It is during thisperiod that the annual reproductive potential of the population is realized. Many traits ofnesting biology of birds are aimed at promoting the better survival of the offspring. However,growth and development of the chicks also depends upon environmental conditions, and theeffect of ecological factors upon natal survival may be equal to that of physiological ones
(O’Connor 1977). Awareness of the principles of nestling development and their ecologicaland physiological requirements allow factors affecting the number, dynamics and sex and age
structure of the population to be defined. The present study aimed at investigating thefundamental principles of development of nestling Steller’s Sea Eagle Haliaeetus pelagicus

A

18

B

Fig. 1. Control measurements of eaglets. A: length of the bill, B: culmenheight and C: length of the hallux claw (mm).

C

under various ecological conditions and to identify factors that affect reproductive success. An
attempt to develop sexing and aging procedures based on body measurements was made.

METHODS
Data were collected at nests of Steller’s Sea Eagle located on the lakes of the Lower
Amur and bays along the north-eastern coast of Sakhalin during seven field seasons (1986 and1989-1994). Development of 71 eaglets from hatching to fledging was observed. Eaglets were
weighed and measured every 4-7 days. Measurements taken included: body weight (g), wing
chord (mm), length of 7th primary (counting from the innermost, mm), length of 1st secondary(mm), length of the bill from its tip to the plumage edge on the front (culmen plus cere mm),
culmen height (Fig. 1) length of hallux (mm), and length of tarsus (mm). Weight and linear
increment was calculated as the difference between two successive measurements divided by
the number of days. Fundamental indices of growth and development of eaglets were definedon the basis of study results and data from hand-reared Steller’s Sea Eagles (Bogdanovich et al.
1994, Tcheredov 1995).
A control sample of 12 individuals (6 males and 6 females, sex defined by chromosome
analysis) older than 70 days was used to investigate relations between morphometriccharacteristics and sex. Sex of birds, as determined in the control sample was used as agrouping variable for discriminant analysis. Results suggested an equation for sex
determination based on morphometric characteristics in birds older than 70 days. This equation
was used to determine sex of birds older than 70 days from a control sample (N = 71), whose
development was watched from the age of month to fledging. Obtained data allowed toestimate analogous discriminant equations for the age of 50 to 70 days.
Eaglet diets (amount, size and species of prey) were studied by analyzing food remnants(cranial bones) collected on and under nests in the course of regular nest inspections. “Reverse

19
calculation” (Vronskiy 1960) allowed specific weight and dimensional composition of prey tobe evaluated. Relation of cranial bones size to body mass and linear dimensions was estimatedby measuring individuals in control samples of 50 specimens for each of the frequently caught
species: Crucian Carp Carassius auratus gibelio, Amur Catfish Parasilurus asotus,
Pseudobargus fulvidraco, and Amur Pike Esox reicherti dybowski. Analysis was performed on
1678 prey remains, collected at 63 eagle nests in 1986, 1989, 1990, 1992 and 1994.
Factors considered critical to eaglet growth rate were: water level, hatching date (andtherefore time of clutch initiation), the numbers of eaglets in the nest, and their sex and age.
MANOVA and covariance analysis were used to reveal relationships between parameters.
Eaglet age influenced the rate and pattern of development. Statistical estimates were madeusing SYSTAT 5.0.
Data on water level in the Amur River were provided by the hydrometeorological station
located in Bogorodskoye village, Ulchskiy district. Shallow areas of the control water body
(Lake Udyl), where Steller’s Sea Eagles hunted, almost dried out when the water level in the
Amur River dropped to 0-30 cm.
Nesting success was calculated as the number of fledglings per territorial pair (birds
which kept to the nest area at least up to the middle of the nesting period and actively built,
refurbished, and visited their nest). This was an index of reproductive potential. The causes of
egg and hatchings mortality were usually unknown. The second index of reproductive success
was the average number of eaglets per successfully nesting pair. This index characterizes theefficiency of the birds’ reproduction in the region.

RESULTS AND DISCUSSION
Eagle’s growth, sexing and aging technique
MANOVA of a control sample of 12 individuals revealed significant differences between
sexes in selected morphometric measurements (P = 0.0001). Accurate sexing based onmorphometric characteristics at an age earlier than 6-7 weeks is impossible. After 6-7 weeks
differences in weight and dimensional characteristics associated with sex become significant.
Linear discriminant analysis yielded the following functions for sexing eaglets in different age
classes:
50-70 days of age: Y = -0.024 × (wing length) + 1.993 × (bill height) + 0.366 × (billlength) - 0.011 × (tarsus length) - 87.202; P = 0.058
70-100 days of age: Y = 0.013 (wing length) + 0.305 × (bill height) + 0.182 × (billlength) + 0.073 × (tarsus length) - 0.065 × (claw length) - 38.948; P = 0.005
If Y is positive, an individual is a female, when negative, a male.
Using these equations, females were 45.07% of the studied population and males 54.93%(N = 71). This does not differ significantly from 1:1 (P = 0.41, χ2 = 0.69). Sex ratio

20

7000

6000

Weight (growth)

5000

4000

3000

2000
1000

0

0

40

20

60

80

100

120

Age (days)
Fig. 2. Curve of the eaglet’s growth.

❍: female,✕: male.

approximating 1:1 is known for Bald Eagles H. leucocephalus (Bortolotti 1984).
Changes in body weight of growing eaglets over the whole nestling period were notconstant. Weight plotted against age yeilded a sigmoidal growth curve (Fig. 2), and were
described by the logistic equations (Mina & Klevezal 1976):
females:males:

Y = 6195 / (1 + 49.21 × e-0.098 × x)
Y = 5117 / (1 + 71.75 × e-0.118 × x)

where Y = body weight (g) and X = age (days).
Development rates of males and females were almost equal during the first 7 weeks after
hatching (Fig. 3). From age > 50-days, the rate of growth declined. This was more pronounced
in males and resulted in further divergence of sexes both in weight and dimensional
characteristics. Weight gain curves can be described by the equations:
females:males:Y = X / (0.868 - 0.0227 × X + 0.00032 × X2)
Y = X / (1.152 - 0.0358 × X + 0.00047 × X2)

where Y = rate of weight gain (g/day) and X = age (days).
Three stages of plumage development during the nestling period can be seen. Hatchlings
are covered with embryonic down of silver-white color. The down is silky and glossy due tohair-like tips of the barbules. Embryonic down is replaced by brownish-gray juvenile down at
the age of 16-18 days. The latter is much thicker and longer with improved insulating
properties. Growth of juvenile contour feathers begins at 31 days post-hatching. It coincides

21
110

Growth (grams)

90

70

50

30

10
10

30

50

70

90

110

Age (days)

Fig. 3. Biomass increment curves for Steller's Sea Eagle.

❍: female,✕: male.

Table 1. Coefficients of growth for Steller's Sea Eagle body elements.

femalesmales

bill length (mm)ab13.9570.416
22.7830.280

bill height (mm)
a
b
8.001
0.368
12.8450.245

tarsus length (mm)ab34.7610.279
47.371
0.200

with the appearance of sheathed stumps of the primary flight feathers. From that time onward,
the growth of the primaries is virtually linear up to 90-95 day age when the 7th primary reaches
its final length, averaging 400 mm in males and 450 mm in females. Growth rates of primaries
do not reliably differ between sexes (P = 0.56) and are described by the equations:

females:males:

primaries
Y = -194.479 + 6.501 × X
Y = -187.489 + 6.365 × X

secondaries
Y = -126.561 + 4.875 × X
Y = -118.487 + 4.776 × X

where Y is feather length (mm) and X is age (days).
Growth rate of bill and legs is greatest in the first 2-3 weeks, after which the rate declines
gradually throughout the nestling period. Growth curves of body elements can be calculated asfollows:
Y = a × Xb, where Y = the length of the body element (mm), and X = age (days), andwhere a and b are variable for each element and are described in Table 1.
Significant differences between the sexes in body development are manifested in 45-50

22
days, caused by a higher rate of development in males. The rate of bone growth declines after
7-8 week. The rate at which male growth slows is greater than that in females (P < 0.001).
The method of aging nestling eagles is based on knowledge of growth processes. In thefirst month (before primaries appear), eaglets can be aged using the rate of development of the
body elements. Bone tissue grows particularly fast during this period (bills and legs reach 6570% of their final length in the first month), and culmen plus cere length can be used todetermine age (P = 0.005). In the period between hatching and 32-34 days, eaglets can be aged
according to the equations
general :females :males :

Y = 0.0412 × X1.614
Y = 0.0244 × X1.751
Y = 0.1810 × X1.235

where Y = age (days) and X = culmen length (mm)Age of older eaglets (> 31 days) can be determined by the rate of development of the 7thprimaries (P = 0.002 for the difference of regression coefficient from 0):
general:females:males:

Y = 31.239 + 0.145 × X
Y = 31.917 + 0.141 × X
Y = 30.610 + 0.149 × X

where Y = age (days) and X = length of the 7th primary (mm).
Shilov (1965), Ricklefs (1968), and Andreev (1990) have shown that the capacity forautonomous thermoregulation by nestlings is extremely low in the period between hatching andthe time when they have attained 15-20% of their final body weight (i.e. 15-20 days for the
Steller’s Ssea Eagles). During this period nestlings are dependent upon adult care. Juvenile
Bald Eagles are able to thermoregulate at an age of approximately 2 weeks (Bortolotti 1984).
Autonomous thermoregulation by Steller’s Sea Eagle nestlings also coincides with thedevelopment of the juvenile down plumage (17-20 days). After that time, the nestlings neednot be brooded if the weather is good. The first seven weeks is a period of accelerated
growth, during which eaglets acquire 75% of their final body weight and 80-85% of final bodysize. Only the growth rate of the remiges and rectricies is constant during the whole nestling
period.
From the age of 50 days, the growth rate of eaglets gradually slows. Males acquire adult
size 7-10 days earlier than females. Body weight increases up to 60-62 days of age in males
and 70 days of age in females. Body growth ceases by 55-60 days for males and 65-70 days
for females. Remiges develop to their full size by 85-90 days in males and 90-95 days infemales. After remiges have grown to their full length, the surface area of the wings forfemales approximates 6730 cm2 (N = 2). Males are smaller. Female eaglets appear to leave
their nest when wing loading reaches 0.95-0.99 g/cm2 (N = 2), but this is likely to varyconsiderably. Body weight usually decreases during the last stages of the nesting period

23
Table 2. Effect of hatching date on eaglets growth rate.
time of hatching
10-15 May
16-20 May
21-25 May
26-30 May
31 May - 5 Jun.
P
P1

daily body weightincrement (g/day)
65.79185.31382.18981.44990.2350.002
0daily wing length
increment (mm/day)
5.773
6.949
7.172
7.038
7.124
0
0

daily culmen length
increment (mm/day).
1.401
1.617
1.69
1.626
1.572
0.023
0.016

P : level of significance of the effect of the time of clutch on the eaglet's growth rate(according to ANOVA)
P1 : level of significance of differences between growth rates of the eaglets hatchedin the period 10.05-15.05 and those hatched later.

resulting in an increase in the juveniles’ power efficiency (Poznanin 1979). Behavior of theyoung birds changes as they grow and acquire flight capabilities. They attempt to jump up andflap their wings at the age of 45-50 days, i.e., when remiges reach 35% of their final length.
However, eaglets are able to fly only 85-90 days post-hatch.
Timing of laying
Artificial incubation of Steller’s Sea Eagle eggs in the Moscow Zoo (N = 6) showed the
incubation period averages 38 days (from the onset of incubation to hatching) (Tcheredov1995). In the wild, females begin to incubate after the first egg is laid, so the time of clutch
initiation may be determined if the eaglets’ age is known. Eaglets hatch in the Lower Amur
Region between 11 May and 3 June. Median hatching date is around 23 May. In the Sakhalin
population, most of the eaglets hatch later and the median hatching date is 28 May.
Extrapolating from estimated nestling ages, the peak of egg laying is about 15 April in theLower Amur Region. The period of egg laying extends over 23 days; the earliest laying date
was registered on 3 April and the latest on 26 April. Coefficient of variation of laying date is
36.56%. Average period of egg laying did not significantly differ between Lake Udyl and theOrel-Chlya lake system located 200 km closer to the sea coast (14.60 ± 0.703, N = 45 and16.00 ± 2.006, N = 21, respectively; P > 0.10). On the north-eastern coast of Sakhalin, eagles
laid eggs 5-6 days later, and the peak of egg laying was 20 April. Egg laying in this part of
Sakhalin differs significantly from that of the Amur population (14.8 ± 0.666, N = 57 and 20.4
± 1.939, N = 14, respectively; P < 0.01). Later laying and hatching dates seem to be associatedwith the later onset of spring in the north of the island.
Analysis of eaglet development under various ecological conditions enabled us toevaluate the effect of some factors on reproductive success. Rate of development and thenumber of eaglets per occupied territory varied significantly with hatching dates. Eaglets
hatched earlier (between 10 and 15 May) grew significantly slower than those hatched later(Table 2). The number of eaglets per brood (registered soon after hatch) correlated negatively

24with the time of egg laying (coefficient of rankcorrelation r = 0.23, P = 0.01, N = 117; Table
time of egg number of3). Fifty-eight nests (49.6%) contained one
Playingeaglets
eaglet, 57 (48.7%) two eaglets, and three eaglets
3-7 Apr.
1.833
0.025
were found in 2 nests (1.7%).
8-12 Apr.
1.857
0.007
13-17 Apr.
1.666
0.09
Comparison of growth of siblings revealed
18-22 Apr.
1.666
0.123
no significant relations between growth rate and23-27 Apr.
1.375
1age (P = 0.405, N = 11), although growth curves*significance of differences between average
numbers of eaglets in broods from clutches
for older eaglets were steeper during the firstlaid in 4 periods from clutches laid between 23
Apr. and 27 Apr. (Mann-Uitney test)
3-4 weeks. Older Bald Eagle nestlings in
multiple-young nests grow, on average, 6%
faster than younger ones (Bortolotti 1988). Covariance analysis of the growth rate of single
Steller’s Sea Eagle nestlings and the younger siblings in broods of two has shown nearsignificant differences (P = 0.05, N = 12). No such differences have been revealed for the older
sibling in these broods (P = 0.12, N = 12). This difference may result from the inhibition of
growth of the younger nestling in broods of two. Growth rate of eaglets did not significantly
differ in broods with one and two juveniles from the age of five weeks (P = 0.71, N = 12).
Table 3. Relation between average
brood size and laying date.

Sex ratio and timing within the hatching period
Time of egg laying was related to sex of hatchlings (P = 0.01). Sex ratio was 1:1 in thefirst five days. More females (58.9%) hatched in the middle of hatching period (the 2nd and3rd five-day periods). In the 4th and 5th five-day periods, 77.8% of hatchlings were males.
Females hatched significantly earlier than males in nests with two eaglets of different sexes(F = 5.11, P = 0.03, N = 24). The same is true for Bald Eagles (Bortolotti 1984, 1986).
According to Bortolotti (1986), fratricide was observed more often in broods where males
hatched earlier than females. In those cases, newly hatched males were larger than females,
more aggressive and grew faster. The earlier hatching of females is assumed to be the result of
selection aimed at survival of the maximal number of juveniles (Stalmaster 1987). Fratricide
is most likely to occur in the first two weeks when differences in sizes associated with thehatching time are most evident and agonistic behavior is most pronounced. By the age of one
month, conflicts between eaglets become less frequent. The rate of fratricide among sea
eagles is still under question. Competition resulted in the death of only one eaglet out of 16
Bald Eagle chicks observed in seven nests (Maestrelli & Wiemeyer 1975). We have examined
19 Steller’s Sea Eagles’ nests with young in 1st down plumage. In only one case, a brood of
three eaglets, did the youngest died of fratricide.

Food requirements
Food requirements of eaglets are closely associated with growth rate and the energy
required to synthesize new tissues. Total energy used by a growing eaglet can be divided into

25

Food requirements (grams)

3000

2000

1000

0
0

10

20

30

40

50

60

70

80

Age (days)

Fig. 4. Food requirements of broods with different number of nestlings. A: brood with one nestling; O: broodwith two nestlings; X: brood with three nestlings. Solid line: fitted curve by the logistic equations, Broken
line: smoothed graph.

that required for growth and feather synthesis, and that needed for maintenance (EM). General
required energy (GE) can be calculated as follows:
GE = ((weight increment of the brood × caloric content of raw biomass) + (EM of aneaglet × number of eaglets)) / 0.7,
where 0.7 is a coefficient of utilization of food by juveniles (Dolnik 1971); caloric
content of raw biomass of the eaglets is 6.70 kJ/g (Dolnik et al. 1982).
Energy of maintenance can be calculated according to the equation (Kendeigh et al.
1977):
EM(30) = 4.472 × m0.6637
EM(0) = 17.342 × m0.5444
EM(Ta) = EM(30) + (30 - Ta) × (EM(0) - EM(30)) / 30,
where m = body mass (g); Ta = ambient temperature (˚C); EM(30) = energy ofmaintenance under thermoneutral conditions, where EM(0) = energy of maintenance under
0˚C; EM(Ta) = energy of maintenance under Ta˚C; (EM(30) - EM(0)) / 30 is heat conductance(kJ/˚C/day).
Food requirements (FI) of the growing eaglets are:FI = GE / (CD × FE),
where CD = specific caloric value of raw matter (average CD of different species of fish

26
Table 4. Nestling eagle growth rates in relation to water levels in hunting areas.
water level (cm)
(1)
(2)
(3)
(4)

0-100
101-160
161-200
201-250
PP1
P2

daily weightincrement (g/day)
78.12291.65590.10577.023
0.000
0.000
0.055

daily wing length
increment (mm/day)
6.829
7.715
7.162
6.256
0.000
0.000
0.026

daily culmen length
increment (mm/day)
1.426
1.409
1.486
1.399
0.208
0.599
0.061

P : index of significance of the effect of water level on eagles' growth rates (according to ANOVA).
P1 : index of significance of differences in growth rates related to water levels (1) and (2).
P2 : index of significance of differences in growth rates related to water levels (3) and (4).

= 5.39 kJ/g (Peredelnik et al. 1972)) and FE = the share of edible fish biomass = 78.7%(Stalmaster & Gessaman 1984).
Food requirements of broods with one, two and three eaglets are presented in Fig. 4 andare described by the logistic equations:requirements of broods with 1 eaglet: Y = 628 / (1 + 9.54 × e-0.0998 × X)
requirements of broods with 2 eaglets: Y = 1573 / (1 + 10.39 × e-0.105 × X)
requirements of broods with 3 eaglets: Y = 2546 / (1 + 10.13 × e-0.108 × X),
where Y = food requirements (g) and X = age (days).
The amount of fish brought by parents to the nest during a 24-hour period may be used as
an indirect index of food consumption by eaglets. Food remains collected in and under nests
were analyzed. Eagles brought an average of 817.01 ± 132.4 g of fish per day to nests with asingle eaglet (N = 29) and 1545.85 ± 207.2 g to nests with two nestlings (N = 32), and thesevalues were significantly different (P < 0.001). Over the whole nest period, average foodrequirements calculated from the above equation are estimated at 587.45 ± 6.85 and 1481.69 ±16.11 g of fish per day for broods of one and two eaglets, respectively. The values for foodbrought to the nest are similar to the values of food required by eaglets in one and two nestlingbroods (P = 0.05 and P > 0.05, respectively).
Affect of water level to the growth of nestling and breeding success
Fluctuations in water level within the hunting areas of adults also affected juvenile
growth rate. Such fluctuations are common in the Amur flood plain in spring and summer,
resulting in differences between the lowest and highest water levels that may exceed 1.5-2 m.
Shoaling of the water bodies caused by lower water levels was shown to result in a decline in
the average weight of the eagle prey (r = 0.59, P < 0.005, N = 18; Masterov 1992). At theother end of the spectrum, fish became less accessible when water levels rose above a certain
level. Both low and high water levels may cause energetic debt in growing eaglets, which, in27
Table 5. Nesting success of the Steller's Sea Eagles on Lake Udyl
average number of eaglets per breeding pairyear number of nests nesting success
1986
101.500 ± 0.167
1989
11
1.545 ± 0.157
1990
19
1.579 ± 0.116
1991
51.400 ± 0.245
1992
9
1.667 ± 0.167
1993
41.500 ± 0.289
1994
14
1.417 ± 0.149

average number of eaglets per territorial pairnumber of nests nesting success water level*141.250 ± 0.218
80.82
20
1.063 ± 0.213
17.85
30
1.200 ± 0.163
72.77
24
0.429 ± 0.202
205.00151.250 ± 0.250
154.58110.667 ± 0.289
9.42
21
1.063 ± 0.193
187.71*average water level (mm) in the period of most intensive eaglet growth : 15 May - 30 June

Table 6. Percentage of different brood sizes in relation to water level*.
Number ofeaglets0
1
2

Water level (mm)0-8080-160160-24040.0 (10) 22.4 (11) 52.8 (19)28.0 (7) 32.7 (16) 27.8 (10)32.0 (8) 44.9 (22) 19.4 (7)Total numberof nests
40
33
37*number of nests (broods) is given in brackets

turn, affects their growth rates (Table 4). Increments in body weight and linear dimensions ofwing and bill during the nest period were significantly lower in both extremely low andextremely high water conditions (except culmen increment in low water conditions). In Bald
Eagles prey delivery rates was related to juvenile growth rate (Bortolotti 1988).
Estimated nesting success of eagles on the lakes of the Lower Amur region during 7 years
averaged 0.986 ± 0.179 fledglings per territorial pair (N = 135) and 1.514 ± 0.126 fledglings per
nesting pair (N = 72). Nesting success by years is presented in Table 5. Nesting successdepends, to certain extent, upon fluctuations of the water level within the hunting areas. A chisquare test of a contingency table (“number of eaglets in the nest” vs. “water level in the first 67 weeks after hatch”) was significant (P = 0.05; Table 6). Nesting success was significantly
greater in years with water levels close to long-term averages. Nesting success tended to
decline and the number of empty nests increase in years when the water level was extremely
high (Mann-Whitney test, P = 0.002, N = 70). Low water levels also caused an increase in the
proportion of abandoned nests (P = 0.15, N = 73). The size of Bald Eagle clutches does notdepend upon feeding conditions. Those conditions, however, significantly affect the number ofsurviving eaglets (Hansen 1987).

LITERATURE CITED
Andreev, A.V. 1990. Ecological energetic of the Arctic chicks. Current Ornithology. pp. 5-21. Nauka,
Moscow. In Russian.

28
Bogdanovich, G.G., Bodyak, N.V. & Vishnevskaya, L.M. 1994. Experience of artificial incubation andmanual raising of the Steller’s Sea Eagle’s (Haliaeetus pelagicus) chicks in the Moscow Zoo. In:
Spicin V.V. (ed). Raptors and Owls in Captivity 3. pp. 5-13. Moscow Zoo, Moscow. In Russian.
Bortolotti G.R. 1984. Evolution of growth rate and nestling sex ratio in Bald Eagles (Haliaeetus
leucocephalus). PhD Thesis University of Toronto.
Bortolotti, G.R. 1986. Influence of sibling competition on nestling sex ratios of sexually dimorphic birds. Am.
Nat. 127: 495-507.
Bortolotti, G.R. 1988. Factors influencing the growth of Bald Eagles in north central Saskatchewan. Can. J.
Zool. 67: 606-611.
Dolnik, V.R. 1971. Productive energy of birds in various phases of their annual cycle. Ecologia 5: 89-91. In
Russian.
Dolnik, V.R., Dolnik, T.V. & Postnikov, S.N. 1982. Caloric value and ability of birds to assimilate food. In:
Dolnik, V.R. (ed). Time and Energy Budgets in Free-living Birds. Leningrad, Academy of Sciences of
the USSR, proceeding of Zoological Institute 113: 143-153. In Russian.
Hansen, A.J. 1987. Regulation of Bald Eagle reproductive rates in Southeast Alaska. Ecology 68: 1387-1392.
Kendeigh, S., Dolnik, V.R. & Gavrilov, V.M. 1977. Avian energetics. In: Pinovski, J. & Kendeigh, S. (eds).
Granivorous birds in ecosystems. pp. 127-204. IBP 12.
Maestrelli, J.R. & Wiemeyer, S.N. 1975. Breeding Bald Eagles in captivity. Wilson Bull. 87: 45-53.
Masterov, V.B. 1992. Ecological energetic and interspecific relations in eagles (Haliaeetus albicilla Lin., andHaliaeetus pelagicus Pal.) in the Lower Amur Region and on Sakhalin. PhD Thesis Moscow State
University. In Russian.
Mina, M.V. & Klevezal, G.A. 1976. Animals’ Growth (analysis on the organism level). Nauka, Moscow. In
Russian.
O’Connor, R.J. 1977. Differential growth and body composition in altricial passerines. Ibis 119: 147-166.
Peredelnik, N.M., Milovanov, L.V. & Erin, A.T. 1972. Feeding fur animals. Kolos, Moscow. In Russian.
Poznanin, L.P. 1979. Ecological and Morphological Analysis of Ontogenesis of Altricial Birds. Nauka,
Moscow. In Russian.
Ricklefs, R.E. 1968. Patterns of growth in birds. Ibis 110: 419-451.
Shilov, I.A. 1965. About stages in individual development of birds. Zoology Zhurn. 44(12): 128-136. In
Russian.
Stalmaster, M.V. 1987. The Bald Eagle. Universe Books, New York.
Stalmaster, M.V. & Gessaman, J.A. 1984. Ecological energetic and foraging behavior of overwintering Bald
Eagles. Ecological Monographs 54: 407-428.
Tcheredov, D.A. 1995. Experience of breeding Steller’s Sea Eagle in 1994. In: Spicin V.V. (ed). Birds ofPrey and Owl in Captivity. Yearbook, Moscow Zoo 4: 45-48.
Vronskiy, V.B. 1960. Materials on the biology of the Amur catfish. Voprosy ichtiologii 14: 34-58. In Russian.