Sunday, March 25, 2012

A fortnight away

For many bird species clutch size increases with latitude, yet throughout their range peregrines (migrants and residents alike) normally lay 4 eggs.

A clutch of 4 eggs is normal throughout peregrine range
Those that breed at relatively southern latitudes have the luxury of time (more than 200 days) and very mild breeding conditions, even to the point that a breeding season can be salvaged by laying a second clutch of eggs if the first is lost.

Typical phenology for migrant Peregrine Falcons in North America

Location Lat  Arrive Lay Hatch Fledging Migration Days
Colorado   39    Mar 10  Apr 10  May 14 Jun 22 Oct 20 224
Ontario 48   Apr 01  Apr 20  May 24 Jul 02 Oct 15 202
Alberta 53   Apr 15  May 05  Jun 08 Jul 17 Oct 05 173
Alaska 63   Apr 20  May 11  Jun 14 Jul 23 Sep 20 153
Nunavut 65   May 23  Jun 08  Jul 12 Aug 20 Sep 17 117

Not so for Arctic-nesting peregrines attempting to raise a brood to independence. The window of opportunity slams shut in a measly 120 days or so, and it's a one shot deal. From the perspective of a Hatch Year bird, the schedule is tight.  Research conducted by Alex Anctil shows a nestling with the best chances of survival will come from the first or second laid egg in an early laid clutch.
Early hatched (July 9), 1 day old nestling, eyes still shut and egg tooth visible
 Almost 3/4 of a nestling's "life" is taken up by incubation (~34 days) and growing time on the nest ledge (~40 days), leaving only 28 days to figure out how to fly and catch at least some prey before their first unknown outward migration begins.

Almost hard-penned (A. Anctil)
For tundra peregrines, the relative ease (presumably) of wintering is close to over...departure for breeding cliffs is only a fortnight away.