Bald Eagle

Bald Eagle

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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.

Departure Dates Arrival Dates Number of Days in Migration Distance Traveled Routes Followed

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.

 

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