The Early Birds (http://www.ccbbirds.org/2014/03/07/early-birds/) (see link for
graph of dates)
By Bryan Watts
Beginning in the 1980s and for many years thereafter, a pair of bald eagles
nesting on Jamestown Island was the first Chesapeake Bay pair to lay eggs.
Known as the "Christmas Eagles," this pair consistently laid around the
Christmas holiday, weeks before their neighbors. The southernmost of the great
Chesapeake tributaries, the James River is still host to the earliest pairs in
the Bay. As the population has expanded, egg dates have continued to advance
to earlier dates than even the Christmas Eagles.
The 2014 bald eagle survey began with eight hours of flying along the James
River on March 5th. The survey team documented several nests with young that
indicate egg laying in December including one two-chick brood that was eight
weeks old, a one-chick brood that was seven weeks old, and a two-chick brood
that was six weeks old. The clutch for the eight-week old brood would have
been laid in late November, a time when most pairs had not even initiated
courtship or nest repair. They were feeding young before almost all other
pairs had begun to lay eggs. The average laying date for pairs along the James
River is February 6th. The early breeding date recorded this year was more
than 4 standard deviation units earlier than the mean, a tremendous jump ahead
of the rest of the population.
These early eagle pairs are extreme outliers within the Chesapeake Bay and each
year they are clustered on the lower James between Williamsburg and Smithfield.
Are these pairs just filling out the tails of the laying distribution as the
population expands or is there some directional movement toward earlier laying
dates? What prey are these pairs exploiting that allow them to raise young a
full month earlier than the rest of the population? Why are these outliers
clustered in a short reach of the James?
The many questions of why and how remain to be explored but, as with most
things, it is the unexpected and unusual that lead to discoveries and make for
a more interesting day.
Michael Wilson
Center for Conservation Biology
College of William and Mary & Virginia Commonwealth University
P.O. Box 8795
Williamsburg, VA 23187-8795
phone: 757-221-1649
fax: 757-221-1650
email: mdwils@xxxxxx
web: www.ccbbirds.org
