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
|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 hard-penned (A. Anctil)|