[Bristol-Birds] Bald Eagle expert suspects we monitored spring migration of Florida birds !
- From: "Wallace Coffey" <jwcoffey@xxxxxxxxxx>
- To: "Bristol-birds" <bristol-birds@xxxxxxxxxxxxx>
- Date: Wed, 27 Jun 2012 14:02:23 -0400
Photo of
female Bald Eagle at SF Holston River 2012 by Vicky Osborne
One of America's leading Bald Eagle researchers believes early spring
observations of eagles seen by our local birders across the Ridge and Valley
Region in Northeast Tennessee and Southwest Virginia in 2012 may have been a
detection of Florida migrants moving north thru the region.
Dr. Bryan Watts, Mitchell A. Byrd Professor of Conservation Biology and
Director of the Center for Conservation Biology at the College of William and
Mary and Virginia Commonwealth University, said published research could
support that.
Dr. Watts attended the recent TOS/VSO 2012 Joint State Meeting at Johnson City.
While it was possible and easy to believe the adults being suddenly seen
throughout the area were from nearby nests, is there another consideration ?
That was a question we asked then. Yes, it appears there were other
considerations.
"Are these Bald Eagles from much farther north that left their areas to migrate
last fall and now returning from their wintering areas and headed to their
breeding ground in the extreme northern part of the country and Canada ?" That
was a question proposed by us in early spring. Maybe not.
A fascinating study by a University of George wildlife graduate student
suggests these may not be eagles that wintered south of us and are returning
north. Rather, data from her study would suggest that what we saw may be birds
from a Florida breeding population which had begun migration north after the
Florida nesting season and were possibly heading north to utilize food
resources after the local food supply in the Florida breeding area had
diminished.
That would mean their migration passed thru our area at a time when we have
eagles nesting with eggs or newly hatched eaglets.
Eventually, we had local reports of a couple of immatures with an adult in the
area well before any local nests could have fledged. Why were these immatures
here and where were they from, we asked in the spring here on Bristol Birds Net.
"What were the ages of the eagles seen?" Watts asked.
He pointed out that important recent research of eagle migration has clearly
discovered a not previously- known fact that our area shares a distinct
component of eagle migration of post nesting season birds coming from Florida
-- pointing out that nesting season begins as early as November in Florida.
Elizabeth K. Mojica, conducted masters research of eagles coming out of Florida
while a student at the University of Georgia. Her paper is published in The
Wilson Journal of Ornithology, 120(2):304-310. 2008.
She used satellite telemetry locations to identify migration routes and
stopover sites of 54 migratory sub-adult Bald Eagles hatched in Florida from
1997 to 2001. She measured number of days traveled during migration, path of
migration, stopover time and locations, and distance traveled to and from
winter and summer areas for each eagle (1-5 years old). Eagles used both
Coastal Plain (24 birds) and Appalachian Mountain (26 birds) routes on their
first migration north.
Science had not previously known that Florida breeding eagles were using an
Appalachian spring and fall migration route. There had been no research to
show that birds moved along a route that included Northeast Tennessee and
Southwest Virginia.
Mojica showed our area to be used as a migration path by tracking Bald Eagles
with satellite telemetry units.
Birds in her study dispersing from their natal area on the west coast of
Florida flew different routes. Telemetered
birds flew thru the Appalachians route as shown at the left in the map from her
published paper.
In regards to the timing of spring migration, the majority of second to fifth
year birds had departed for migration by at least the last couple of weeks of
April. She followed birds for several years in both north and south migration.
This is an interesting study that may suggest that our birders, suddenly
detected an influx of passage Bald Eagles in late March thru April and early
May and were on to something. Perhaps, we had more than a wild imagination.
We felt like we were clearly seeing a sudden wave of Bald Eagle reports across
our area by established birders.
The weather conditions at that time this past spring were clear and we think
there was a south wind to aid their flights.
The graph at the left was published by Mojica and included other bars in her
illustration regarding different age classes. By our removing all other graph
information except those she showed for 2nd to 5th year northbound (number of
eagles 36) it allows the readers of this e-mail to more clearly see the
numbers of eagles departing by two-week increments from her Florida study area
and beginning migration north.
Thanks to the following birders who reported important sightings of eagles
other than those suspected to be local breeding birds: Rob Biller, Wallace
Coffey, Glen Eller,
Roy Knispel. Rick Phillips, Harold Smith, Trudy Smith, Susan Hubley, Jennifer
Meade, Michael Sanders, Brookie Potter and Jean Potter.
Mojica's research also clearly detected that about half of the northbound Bald
Eagles during spring migration made stopovers at various points and stayed for
a period of one to four or five weeks. This is almost identical to the
stopovers of Osprey we have been monitoring along the South Fork Holston River
during April for the past three years. She found and mapped many stopover
locations in the Coastal Plains eagle migration areas east of the Appalachians.
The eagle stopover locations detected in the Appalachian eagle northbound
migration route in spring were north of us in West Virginia and farther.
However, that is only stopovers she detected. Her paper acknowledges that
problems with timing for downloading data may have missed other stopovers. It
does not mean we do not have stopovers of migrant northbound eagles in our area
during spring.
WHAT WE TAKE FROM THIS
(1) We have found established research to show that northbound eagle migration
from post-breeding eagle populations pass thru our area March to May. We can
now be alert each spring for Bald Eagle migration along the mountains and
especially in the upper Tennessee River drainage and its important tributaries
which include a number of significant Tennessee Valley Authority impoundments.
Also those in Southwest Virginia and especially Hidden Valley Lake and Laurel
Bed Lake along Clinch Mountain.
(2) We are in their Appalachian path which, at this time, is almost exclusively
shown to be Northeast Tennessee for that state. It is a western component of
the same population's migration thru Virginia which is migrating here in
Southwest Virginia because part of the Florida population migrates along the
Coastal Plain of Virginia east of the Appalachians.
(3) Those of us documenting the suddenly-expanding Bald Eagle nesting
population in our area must begin to map eagle core nesting territories from
December thru January and realize that pairs on territories must clearly be
determined separate from the Florida northbound vagrants passing mostly after
January. Also, that we may well have stopover eagles staying with us for weeks
during this period and they may confuse us with possible nesting eagles. We
need to coach and remind area birders to carefully record and report to our
lists eagles in this restricted Northeast Tennessee eagle spring corridor.
This is an important example of how systematic reporting of observations can
assist science and the study of birds -- especially an important species such
as the American Bald Eagle !
(4) The popular use of computers and the internet has allowed us to develop
valuable tools of communication such as Bristol Birds Net. If we expand the
use of such a tool to help coach and educate birders and gather an analyze
data, rather than to only promote social themes and drive popularity and
functions of bird clubs and individuals, we open up an entire new realm of
involvement and enjoyment. Without birders having and using technology
(computers) and the swift -- almost real time reporting of bird behavior and
movement -- we would not be able to even imagine or participate in anything
similar to the Bald Eagle migration. We also can exchange data and discussions
with prominent ornithologists and experienced birds in seconds (and daily) at
the tips of our fingers.
Special thanks to Dr. Bryan Watts for much time he has spent discussing eagles
and Peregrines with us and for providing the research paper by Elizabeth
(Libby) Mojica who is now on his staff at Williamsburg.
Wallace Coffey
Bristol, TN
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