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Bald Eagles of Alaska - Section: 13 Page: 95 - Perspectives on the Breeding Biology of Bald Eagles in Southeast Alaska

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Perspectives on the Breeding Biology of Bald

Eagles in Southeast Alaska

Scott M Gende
U.S. Forest Service, Forestry Sciences Lab., Juneau, AK

Southeast Alaska (hereafter Southeast) has one of the highest densities of breeding Bald
Eagles in North America (Gende et al. 1997). With relatively pristine habitat, low levels
of disturbance and minimal contaminant influence, Southeast is a prime area to study
factors that naturally regulate population levels, reproduction and general ecology of Bald
Eagles. My several years of field research with hundreds of hours of observation of Bald
Eagles have led to some perspectives on the breeding biology of eagles in Southeast. I
will discuss some of these observations in context of other research that has been done on
the life history of Bald Eagles and suggest potential topics for future research.

Three distinct stages of reproduction for eagles in Southeast will be discussed: pre-laying,
incubation and nestling. The post-fledging period is also an extremely important period
as fledglings exhibit the highest rates of mortality during the first year out of the nest
(e.g., McCollough 1986, Hodges et al. 1987). Although I have observed adults feeding
fledglings for 3 weeks after they leave the nest, I have little insight concerning the post-
fledging ecology and thus will not discuss this period (I). (The numbers in the text such
as (I) refer to text found in the section entitled Potential Research Questions). All related
research questions are listed by number at the end of the manuscript.

Pre-laying

The pre-laying stage of reproduction is the time when nesting activities resume in the
spring (e.g., courtship, talon-locking, nest building) to the time just before females lay
their first egg. The pre-laying period cannot be defined as the time breeding pairs arrive
on the territories, because the population of adult eagles in Southeast is thought to be
non-migratory (Sidle et al. 1986). Some sub-adults will migrate south during the winter
but many adults stay and, in fact, exhibit fidelity to their nest sites throughout the winter
(Hodges et al. 1987, Kralovec 1994). This does not mean territorial adults will not stray
from the territory. On the contrary, eagles are often on the move in the winter, traveling
between food patches (e.g., to the winter chum run in the Chilkat River) for up to 10 d at
a time (Kralovec 1994). Throughout the winter, pairs will return to the nest territory for
brief periods to re-establish their claim. For eagles to be non-migratory, there must be
sufficient food during the winter. Sporadic trapping efforts have provided some evidence
that food levels in Southeast are sufficient during the winter. For example, in January
1995, Phil Schempf and I trapped an adult female that weighed nearly 7.4 kg, much
heavier than normal mass estimates of eagles.

95

OCR
Tag: chilkat contaminant ecology fledging fledglings hodges juneau kralovec mccollough nestling postfledging

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