HANCOCK FORUM NEWSLETTER Issue No 4 ~ October 24, 2007Editors: Cobbler39/Blue Heaven__________
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FEATURE STORYEAGLE MIGRATIONThe
only thing we know for sure about the migration of southern British
Columbia Bald Eagles is that they go somewhere for a few weeks every
year. The nesting areas are vacated sometime after the young have
fledged in August. Because the eagles in this area have not been in the
endangered category (protected, yes), funding has not been provided to
do costly telemetry studies of the eagle population in B.C. Birds have
been banded, but the low incidence of banded birds and reports has
resulted in small amounts of scattered information.
After
fledging, the young are still dependent on the adults to feed them for
a period of up to a couple of months until they gain the experience and
skills to find and catch their own food.
The eagles of northern
Vancouver Island and further up the coast leave a bit later than the
southern Vancouver Island and Fraser Valley eagles but, one thing is
certain: the migration includes adults, newly fledged eaglets, and any
other non-breeding eagles.
Tracking Bald Eagles Since 2004, Destination Eagle in the province of
Ontario has
tracked the journeys of 13 eaglets. These eaglets have traveled
extensively but the majority of their time has been spent in the lower
Great Lakes basin where they originated. These young birds spend a lot
of time in contaminated “hotspots” and suffer a high mortality rate.
The
United States has done more extensive telemetry studies of eagle
migrations. The birds are fitted with tiny backpacks that hold a
lightweight satellite transmitter that beeps every 10 days. In this
way, the travels of each bird can be mapped.
The Santa Cruz Predatory Bird Research Group (SCPBRG) at
UC Santa Cruz
is tracking juvenile bald eagles as they make fast migrations covering
thousands of kilometers. The first bird tracked flew some 900 miles in
August from its nest at Lake Shasta, in northern California, to the
vicinity of the Dean River in central British Columbia. The journey
took less than three weeks.
So far, the juveniles they have
followed have traveled thousands of kilometers from their birthplaces
in California to British Columbia and one to the Great Slave Lake area.
The
young eagles forage for dead salmon and learn to hunt for live prey in
the late summer and fall. The SCPBRG says these stunning first journeys
from the nest are honed by thousands of years of instinct. It is a
remarkable coming-of-age quest for food and independence.
Studies
of migration routes by tagging wintering bald eagles over several years
in cooperation with the California Department of Parks and Recreation
at Millerton Lake near
Fresno, CA,
have shown that virtually all of these eagles migrate to a relatively
consistent area within Canada's Northwest Territories, northern
Alberta, and Saskatchewan for the summer.
The map below shows a
journey which is similar to many others in the study with an adult
female traveling north to her breeding ground at Great Slave Lake in
the Northwest Territories. The eagles' return journeys are along much
the same routes as the northward ones.
...Backpack
photo: Journey North 2000Satellite monitoring of adult eagles in the
Skagit River area
in Washington State shows a different picture. Their findings document
a spring migration (16 February to 5 April, n = 25 movements), and fall
migration (8 August and 14 December, n = 5 movements) with the eagles
migrating along the coastal corridor from Washington to southeast
Alaska, and through interior British Columbia along the Fraser River.
Of 20 telemetered eagles, 40% originated from British Columbia, 35%
from Alaska, 20% from the Northwest Territories, and 5% from the Yukon
Territory.
Radio-telemetry studies of a few Bald Eagles reared in
Oklahoma show that they migrate north during the hottest months of the summer to cooler climates such as the Great Lakes area or Canada.
Not
all eagles migrate. No one knows how newly fledged eagles know where to
go or if some just wander. They usually leave before their parents. It
is believed that these are innate (inborn) behaviours. Not all
fledglings return to their birthplace.
Eagles ride the thermals
(columns of rising air) to high altitudes, then fly long distances at
speeds up to 50kph (30mph), soaring on the wind currents until they
catch the next thermal and gain altitude again. There can be streams of
eagles in the sky, with the birds spread out for many miles.
Where do the eagles of British Columbia go?This map shows that Bald Eagles are year-round residents of Vancouver Island, the B.C. coast, and southern Alaska.
However,
it doesn’t explain where the adult eagles of the Saanich and Hornby
Island nests go between fledging and fall nest-building. They don't
leave in August to go to the salmon runs because they are back at their
nests before the salmon spawn.
The Stanley Park Ecology Society
is monitoring 17 nests in Vancouver, B.C. They say that many adults and
juveniles move to nearby rivers (and their fish runs) as a stable food
source.
Gradually, adult eagles are spotted again towards the
end of September. The adults return to nesting areas around the
beginning of October, plus or minus one week, to reclaim their nest
territory. Mid-October to mid-November is nest-building time. They
bring large branches to place around the outside of the nest and
smaller branches and material for the inside.
The immature
eagles straggle back a bit later. This is winter survival time. Colder
weather and shorter days are occupied with getting food. Nest-building
stops. They depend mostly on fish during this time but also prey on
winter-weakened birds. The Bald Eagles gather at the many streams and
river estuaries to feast during the annual salmon spawning in fall and
winter.
ConclusionThe
only time of year that Bald Eagles are absent from Pacific Northwest
areas is August/September. I would like to think that the juveniles
have set off on the first great adventure of their lives and that the
parents take a well-deserved flying holiday (remember Mom's tattered
and weary appearance after Sidney finally fledged). They ride the
thermals and touch down to forage for food until instinct tells them it
is time to join their partners back at the nest and meet up at the
rivers for a salmon feast.
Blue Heaven
read on for the rest of the newsletter...
... LETTER FROM THE EDITOR
Dec2
3:08pm 
BH
4:36pm
... 
Salmon spawning, Tapedira
