Orange-crowned Warbler
This 
wide-ranging North American songbird
is the focus of an in-depth demographic study comparing highly migratory birds in Alaska with short distance migrants on the Channel Islands off southern California.
The Alaskan birds are part of a subspecies that ranges across the boreal forest of North America, from Alaska to Newfoundland. The benefit to nesting so far north is a bounteous supply of insects to feed their young and long June days in which to forage.
The cost is a short breeding season before cold weather kills off their insect food. They must undertake a perilous migration to and from the wintering grounds in Mexico and the Gulf Coast every year.
In contrast the warblers that nest on the Channel Islands have a much longer breeding season as the climate is quite moderate. In addition, their likely wintering grounds are only a few miles away in mainland southern California and Baja Mexico.
Our studies have shown that the same species of bird adopts different strategies in different areas.
For example:
- Alaska birds lay 5-7 eggs in a nest; California birds lay 2-4.
- Alaska birds nest once every year; dry years in California mean some birds may forgo nesting while in wet years they may nest twice.
- California birds live longer.
One interesting discovery from this research project is that the subspecies that nests on Catalina Island is the only population that nests in trees. All other orange-crowned warblers nest on the ground. Find out why
