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Ray Brown, Refuge Biologist
8/1/06
Eagle Update - 8/1/06 - Bombay
Hook's Eagle nest produced one fledgling this year. The bird
fledged between June 14 and June 20, 2006. The young seemed large
and strong and had been branching out in the nest tree for weeks.
We had high hopes that Bombay
Hook’s eagle pair was finally
going to nest successfully last year after an eight year long series of
failed
nesting attempts. The last year that
eagles nested successfully on the refuge was 1997, when one eaglet was
produced.
In 2005, eagles again appeared to
be setting up residence at
the previous year’s nest deep in the woods on the west side of
Shearness
Pool. The birds were seen at the nest a
number of times early in the year and were exhibiting a moderate degree
of
territoriality and fidelity to the nest site.
We were hopeful that the pair had produced one or more eggs but
we were
not able to confirm it. When the time
came for the eggs, if present, to have hatched, the eagles apparently
abandoned
the nest and have not been seen there since.
In the
winter of 2005-6, activity at the nest seemed to be
increasing again, based on the presence of fresh whitewash (excrement)
found
under the nest tree and adjacent trees, and the presence of prey
remains in the
area. However, no eagles were seen at
the nest site so it appeared that birds were again only making a
half-hearted
attempt at nesting.
Then on the
weekend of January 28-29, two refuge visitors
separately reported seeing a large nest with an adult bald eagle near
the Allee
House. Other visitors may have seen the
nest earlier but did not report it. Refuge
staff located the nest on January 30 and have observed one or two adult
bald
eagles regularly associated with the nest since that time.
This time
the eagles seem to be more intent on nesting than
in recent years. In early February, an
eagle was observed sitting in the nest in an incubation posture,
spawning
speculation that the female had laid at least one egg in the nest. From then until mid-March, the eagle pair
took turns sitting in the nest, presumably incubating one or more eggs. The suspected “due date” for the first of
these eggs, if indeed there were any present, was around the Ides of
March.
On March 17,
an adult bald eagle was observed standing in
the nest, intently staring at something in the nest.
Soon the other member of the pair arrived,
and both eagles stood in the nest staring at some apparently new object
in the
nest that intrigued them. Could it be that
an egg was hatching or that an eaglet had recently hatched out?
On March 22,
an adult eagle was observed delivering two
different prey items to the nest 40 minutes apart, while its mate
remained in
the nest. One of the prey items was a
fish,
but the other one could not be identified because of the distance of
the
observer from the nest (over 2300 feet!).
The eagle in the nest proceeded to tear at the prey items,
turning its
head to the side every now and then as if feeding a small eaglet down
in the nest. Could it be that the refuge’s
eagle pair has
successfully produced young after so many years of failure?
Even if
eaglets are in the nest, they’re not out of the
woods yet, so to speak. Eagles in Delaware have experienced a slower recovery than
eagles
in other parts of the country, leading to speculation that persistent
pesticides and other contaminants produced and used in the Delaware River watershed in the last century may
still be affecting the
reproductive success of these majestic birds.
Eaglets also fall prey to various avian and mammalian predators,
such as
raccoons, hawks, owls, and crows, or may starve because of an
insufficient prey
base or inattentive parents.
Nest failure by eagles also can often be
attributed to human disturbance near the nest.
Individual eagle pairs have their own tolerance limits when it
comes to
human or equipment presence near the nest.
For example, some eagles have nested successfully for years near
major
highways or developments, whereas other eagles have abandoned their
nests when
a construction or timber harvest project has occurred near the nest. Bombay Hook’s eagle pair has demonstrated to
be intolerant of human presence near the nest, often flushing when
humans have
come within sight of the nest tree, even long distances away. The eagles’ intolerance for human presence
near their nest is the reason that Parsons Point Trail is typically
closed
during the nesting season—to keep visitors away from the historic nest
location
on Shearness Pool. The refuge will be
undertaking additional management modifications (including area
closures) and
monitoring activities to ensure that the eagle pair has the greatest
probability of nest success this year.
The eagle nest can be viewed best from two
locations along Dutch
Neck Road. The
first viewing location is directly in
front of the Allee House. The nest is
about 2100 feet south-southeast of this location. The
second viewing location is about 0.25
mile east of the yellow gate by the Allee House. The
nest is about 2350 feet south-south west
of that location. Posts have been
erected at this location to aid in sighting in on the nest. The eagles have not yet shown signs of being
disturbed by single observers or small groups at either location. The nest can be seen with the naked eye from
either location, but a spotting scope is needed to observe eagle
activities at
the nest. Nest observations are best
made early in the morning before the sun heats the air and causes too
much
distortion.
The area around the eagle nest has been closed
to visitors to prevent disturbance to the eagles and to afford the
eagles with
the greatest opportunity to successfully raise young this year. We also ask that persons and groups viewing
the nest remain respectful of the eagles and try to minimize their
visual and
audible disturbance in the area.
Remember that even though the nest is over one-third mile from
either
viewing location, the eagles can still see people and vehicles at
either
location, and can hear loud noises from those locations if the wind is
right.
To help keep track of the status of the nest, we
will be installing an eagle observation record box at one of the
viewing
locations mentioned above. You can help
us monitor the progress of the nest through the nesting season by
writing down
your observations on the datasheets on the clipboard inside the box. We expect that eaglets will be confined to the
nest until at least the early May, at which point they should start to
“branch
out” in the nest tree in preparation for fledging.
The young eagles are expected to leave the
nest tree and take their first flight some time in the first two weeks
of
June. The immature and adult birds
should remain in the general area around the nest for about two months
after
fledging, as the parents still feed the young during that time. After that, the young will probably disperse
from the area.
References:
Buehler, D. A. 2000. Bald
Eagle (Haliaeetus
leucocephalus). In The Birds of North
America,
No. 506 (A. Poole and F. Gill, eds.). The Birds of North America, Inc.,
Philadelphia, PA.
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