Where have all the birds gone?...

Well, here's what Lake Michigan looks like right now, at least at North Point Marina:

And again at Southport Park, in Kenosha County, Wisconsin:

With below zero weather for several days, inches of snow on the ground, and little if any open water to be found, you'd expect slim pickings for birders right now, right?

And compared to spring and summer, of course, you'd be right! But....

here's the view from the south end of Waukegan Harbor yesterday:

 

And, yes, those are birds -- Herring and Ring-billed Gulls, to be precise. And here's a closeup view of one hopeful bird from Southport Park today:

Ring-billed Gull (Larus delawarensis), Southport Park, Kenosha Co., WI, 1/9/2014.

 

As any birder to put on a pair of snow boots knows, some birds manage to winter, even here in frozen Chicago. Some even come south to spend the winter in our "balmy" climes!

 

Now, the life of a migrant songbird sounds great -- Blackpoll Warblers spend the summer in Maine, and the winter in Brazil. I can imagine quite a few of us would love that schedule. Except that the birds don't get to hop a 747 to get there. They have to make it the whole way on their own two wings, which is an incredibly energy-expensive task -- every fall, Ruby-throated Hummingbirds double their weight on the Gulf Coast, then burn off every bit of that weight flying to the Yucatan.

 

So we're left with two questions -- why leave? And the one faced by every Hawaiian vacationer, why go back?

 

The first question seems easy -- it's cold up here! But in fact, feathers are very good insulators, and birds as small as Boreal Chickadees and Hoary Redpolls happily winter in central Canada. Most migratory birds are fleeing starvation, rather than cold, as their summer food supplies (fruit, flying insects, smaller birds) aren't available during a cold winter. Those birds that stick around do so by exploiting food sources that are always available. (Everything from seeds and insect larvae to mice and carrion.)

 

But there's always food in, say, central Mexico. So why come back?

 

Well, a glance at a map of North America will supply part of the answer. Notice how it's funnel-shaped, wider up north than down south? That means that there's a lot of room up there, so it's relatively easy to find a breeding territory. Down in Mexico, the local breeders don't see any reason to leave, so every spot is going to be taken. (Many tropical birds hold year-round territories, and live longer than their migratory counterparts, so territories are in short supply.) Up in Nunavut, the land's there for the taking, just as it was in the homestead era.

 

The rest of the answer is the flip side of the long, cold, winters. When the sun does come back, it does so in abundance -- even here in Chicago, we get 16 hours of sunlight per day in late June, and that only increases as the birds move north. Most passerines are only active in the daytime, so the longer the sun's up, the more insects they can catch and stuff their babies with, and the more offspring they can produce. And as long as the increase in offspring more than matches the decrease in survival due to migration, they'll continue to do so.

 

The spectacle of avian migration is something every birder looks forward to, whether it's skeins of geese and Sandhill Cranes filling the sky with laughter, flocks of warblers like flying flowers in the trees, or kettles of Broad-winged Hawks seemingly ignoring gravity on their way north. Memories of past migrations hold out the promise that these quiet days of cold and ice will end soon enough.

 

 

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