My hummingbirds vanished weeks ago. I miss them. The chipping sparrows that sang from tall pines near the pool parking lot all summer are gone. Most warblers left in September. As day length and temperatures change, leaves change color, and fall migration gets underway.
We think of the birds that nest here as “our birds,” but whose birds are they? Most migrants are here for less than half the year. Baltimore orioles spend more time in Costa Rica than they do in Maryland. The best looks I ever had at yellow-throated warblers were in Jamaica in January.
Many bird species migrate thousands of miles twice a year. Why do they do that? Because they can. It’s mostly about food, of course. They move north to find expanded breeding territories and plenty of insects to feed to babies. They return to southern climes for insects that prosper in those warmer winters. But how do birds know? How do they find their way?
Testing has shown that birds have many navigational tools. A biological GPS, a map sense, helps them navigate. Their inner compass helps them distinguish north from south. They can use the positions of stars and sun, the earth’s magnetic field, local scents, low-frequency sound detection, and even ocean wave patterns.
Flight plans vary. Some species, like robins, travel in flocks, stopping to rest and feed for a few days before moving on. In fact, robins may not even move very far south, if they find enough fruits and berries. Some species, like many shorebirds, do long non-stop flights. Weather affects the flights: cold fronts may hold up migration; winds may blow birds off-course.
But once they get as far south as they want to go, how do they know whether their favorite place is east or west of where they are? Perhaps it’s their own memory of places and routes. Not all questions are answered; scientists are still learning how birds do what they do so well.
With cold weather on its way, I’m feeling grateful for the birds that winter here with us. We have wonderful backyard birds who reside here year-round: cardinals, titmice, doves, and woodpeckers, to name a few stalwarts. House wrens migrate but Carolina wrens stay. Woodpeckers stay because they can pry insects from under winter bark; cardinals and other seed-eaters stay to hunt for crunchy seeds and freeload at our feeders. They are joined by a few species like white-throated sparrows and dark-eyed juncos that nest in the north but have moved south to share our milder winter. They’re familiar annual visitors who help us through the dark times.
Now that twigs are rattling in our mostly leafless trees, I remind myself: our summer birds may have left town, but we still have avian bright spirits to bolster our courage against impending winter. The birds and the seasons are moving as they should.