Raptor View Research Update December 5, 2012 Adam Shreading

Raptor View Research Update
December 5, 2012
Adam Shreading
Now that fall migration has come to a close, we have turned our attention to
birds wintering on the MPG Ranch. Last year we outfitted two adult Golden
Eagles with GPS transmitters. After spending their summers in Alaska, both
birds returned to the Bitterroot Valley in early November. This winter we
will increase the scope of this project, and hope to outfit up to 10 additional
adult Golden Eagles.
A second-year female Golden Eagle approaches the bait. This photograph was taken approximately
one minute before we fired our net-launcher and captured the bird.
With eagle in hand, we reset our net-launcher moments after capture.
We take a blood sample from each captured eagle and test it for lead
concentrations. Lead poisoning is a documented problem in birds like
eagles, ravens, condors, and vultures. The most likely sources of
contamination include fragmented lead-core bullets found in gut piles and
lead shot used in bird hunting. We analyzed blood from 163 eagles from
2006 -2011 and found over 50% of individuals had elevated blood-lead
levels. Because lead only stays in the blood for a few weeks before being
absorbed into the body, we expect to see higher blood-lead levels in eagles
tested during/shortly after hunting season than those tested at other times of
the year. Though our sample size is low, our preliminary results show this
trend.
Blood/Lead Levels of Eagles Wintering in the Bitterroot Valley Concentration of Lead (μg/dl) 60 50 40 30 20 10 R² = 0.21129 0 Blood/lead levels of 15 eagles tested in the Bitterroot Valley of Montana since December, 2011. The
origin marks the approximate end of the general big-game hunting season in Montana. Stages of
exposure include: Background (0-10 µg/dl), sub-clinical exposure (10-60 µg/dl), clinical exposure (6090 µg/dl), and acute toxicity (90+ µg/dl).
We have captured two Golden Eagles so far this season; both were in the
range of sub-clinical exposure.
Date
Captured
11/29/2012
12/4/2012
Blood/Lead Levels
Species
Age
Sex
(µg/dl)
GOEA Second Year Female
16.8
GOEA
Hatch Year
Male
34.3
Eagles Captured on the MPG Ranch This Season
This winter we will be applying wing tags marked with individual-specific
numbers to those Golden Eagles not outfitted with GPS transmitters. Since
2004, Raptor View Research Institute has put over 180 sets of wing tags on
Golden Eagles. To date we have a reencounter rate of ~17% -- significantly
higher than the ~6% rate from bands alone. We hope to increase our number
of resightings this season with trail cameras set on our baits.
The visibility of wing tags allow eagles to be individually identified even from a distance.
The carcass cameras often provide us with images of other scavenging
species.
This Rough-legged Hawk spent 1-1.5 hours feeding off our bait on two separate occasions.
While Red-tailed Hawks are known to scavenge, observations of this behavior are rare.
Golden Eagle Tracking:
After spending their summers in Alaska, both Golden Eagles outfitted with
GPS transmitters returned to the Bitterroot Valley in early November, and
have already been recorded on the MPG Ranch this winter. As our dataset
grows with additional outfitted eagles we will be able to geo-spatially
analyze winter habitat use of Golden Eagles in the Bitterroot Valley.
Movements of male (in blue on left) and female (in red on right) adult Golden Eagles. Squares
represent locations from 2011 while circles represent locations from this winter. The inset shows the
approximate 80-mi2 area of concentrated use around the MPG Ranch.
Osprey Tracking:
The adult male from the North Center Pivot nest arrived on his wintering
territory Oct. 5th 2012 along the tropical coastal plain of east-central Mexico,
30 mi from the Gulf of Mexico, 3.5 mi from the very small town of San
Rafael. Surrounded by agricultural fields, he is residing on a very small lake
that encompasses an area of only 0.5 mi2. There he spends the majority of
his time fishing and roosting along a slough on the SW shore close to a dirt
air strip. With only himself to feed, his winter territory is much smaller than
his summer range in the Bitterroot Valley. We have our fingers crossed he
makes it through winter and survives his long spring migration back north to
his breeding territory on the MPG Ranch.
Polygon represents the area most frequently used.
The adult male from the Ranch Entrance Nest arrived on his wintering
territory Oct. 7th 2012 on the Gulf of California’s coast in northwest Mexico,
roughly 10 mi SSW of the municipality of Los Mochis. The region is
surrounded by miles of agricultural fields. Our male spends most of his time
on the small islands and water estuaries just off the mainland coast. Here he
presumably fishes unmolested and away from most human activities.
Weather at the time of this writing was sunny and 79°F.
Polygon represents the area most frequently used.
The adult female from the Ranch Entrance Nest boasts the farthest migration
movements of any of the instrumented Osprey, now residing along
Nicaragua’s south west coast. She arrived on her wintering territory Sept.
25th 2012 and appears to be doing great. She spends most of her time fishing
along the rocky coastal cliffs near the town of El Ostional. Like the other
adults, her wintering territory is roughly 25 mi2. The exception was a 45mile, eight-hour round trip jaunt over the bay on Nov. 2nd. Even though she
winters on the Pacific Coast of Nicaragua, her fall migration route was
essentially identical to the North Center Pivot adult male wintering along the
Gulf Coast of Mexico. This route included a two-day journey across the
Chihuahuan Desert and Sierra Madre Mountains before reaching the coastal
plain of eastern Mexico. At the time of this writing it was sunny and 84°F
on her wintering grounds.
Polygon represents the area most frequently used.
On Oct 2, 2012 the smaller (at time of banding) of the two young from the
North Center Pivot Nest young arrived along the Gulf Coast of Mexico, less
than 100 mi south of the border near the town of El Americano. This
farming and fishing municipality has a population of just over 100,000 and
is centered less than 10 mi from the Gulf. It spends the majority of its time
fishing the beaches of the many coastal estuaries of the area, occupying a
winter range of roughly 25 mi2. At the time of this update, weather was
sunny and 73°F.
Polygon represents the area most frequently used.
After spending nearly 60 days fishing the numerous slow water sloughs of
Marlow, Oklahoma, Young 1 from the Ranch Entrance nest headed south on
November 12th. On Nov. 19th, seven days and 430 mi later, it reached the
Gulf Coast of Texas, approximately 35 mi north of Corpus Christi. After
staying just one day, it slowly headed E-NE along the Gulf Coast,
presumably looking for suitable fishing areas. Fortunately, National Wildlife
Refuges make up much of this coastal region. It spent about four days in
Matagorda Bay area, before heading E-NE on the 25th. Currently it appears
to have settled just off the Brazoria National Wildlife Refuge, about 50 mi
south of Houston, less than ten mi from Galveston Island. It looks to be near
a fish hatchery. At the time of this writing it was 78°F and sunny.
Polygon represents the area most frequently used.