Summary of Spring
Migration Findings
Peter Nye
The following summary is based on satellite
data from 11 Bald Eagles that were tracked for multiple years; one for
4 complete springs.
Data on total of 57 seasons: 35 spring season, 22 fall seasons.
Spring
Migration Departure Dates
- Bald Eagles
leave New York over an 8 week period.
- The median
departure date is March 18.
- The majority
of birds depart during a 2-3 week period in March.
- Females
leave later than males (median is 5 days later).
- Eagles
left earliest from New York’s southern-most study site
- Mongaup),
during the first week of March.
- Eagles
left latest from New York’s northern-most study site (St. Lawrence),
3 weeks later, March 24.
Spring
Migration Arrival Dates
- Eagles
arrive over an 8-week period, between March 9 - May 2; (median April
5).
- The median
arrival of females is a week earlier than males (so they are leaving
later and arriving earlier).
- New York’s
southern-most study site (Mongaup) arrived latest (and left first!).
Number
of Days in Spring Migration
- The average
of all Bald Eagles studied took 18 days migrating to summer areas.
- Males
took longer (26 days) than females (13 days). (Makes sense for females-they
are leaving later and arriving earlier; takes less time).
- Mongaup
Valley birds taking significantly longer than all other areas: 37 days
versus 12 days.
Distance
Traveled
- The mean
distance for all eagles = 1039 km
- Great
range of travel distance: 298 km (St. Lawrence adult female) versus
1914 km (Mongaup adult male).
- Males
travel significantly farther than females. No surprise, they left earlier,
arrived later, and took longer to get there.
- Mongaup
Valley eagles moved significantly farther than all other locations (Also
makes sense: they early departure, greatest total days in migration,
latest arrival date).
- St. Lawrence
eagles shortest average distance to summer grounds, consistent with
late departure, short travel time and early arrival date, averaged only
727 km move.
Routes
followed:
- Followed
compass headings pretty directly and appeared to take direct and quick
route in spring (compared to fall; wander, longer time).
- Sometimes
followed major water courses (rivers or coast). Atlantic coast, St.
Lawrence River, Ottawa River, and Great Lakes--major landmarks used?
- All but
one (of 21) summered in Eastern. Canada: 1 found to be Adirondack resident
– only one!
- The majority
traveled north and northeast.
- No differences
based on gender.
Copyright
2003-2004 Journey North. All Rights Reserved. Please send all questions,
comments, and suggestions to our feedback form
|