The new birding challenge: instead of seeing the bird once to check it off on a list, try to understand what is happening in the birds' world.
I live in a world-class hotspot for bird migration. So much is going on here that I can't possibly learn every detail, but it's exciting to try.
My goal is to gain some new insight every day - to never stop learning about the fascinating lives of migratory birds.

Sunday, April 22, 2012

Question: Differential timing, sparrow version

Fox Sparrow (eastern, or "Red," population):  We know it's an early migrant, and that makes sense, but we don't know why some sparrows are later.  Photo by Kenn Kaufman.
April 22: Thinking today about two species of sparrows and their migration through NW Ohio.  Numbers of White-throated Sparrows are just now starting to build up, while the peak of Fox Sparrow migration is already well past.  This timing is already well known.  But I'm wondering: why does it differ so much between these two species?

White-throated Sparrows and the eastern population of Fox Sparrows have similar ranges in summer and winter.  They nest in boreal forests across Canada and winter in the eastern United States. White-throated Sparrow has a broader range at both seasons, with its breeding range extending well south into the northeastern U.S.and its wintering range extending north to the Great Lakes.  (Look at any field guide that has range maps to see what I mean.)  Still, their overall distributions are similar.  Hence my question: why do the Fox Sparrows move north a full month earlier, on average, than the White-throated Sparrows? 
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