My little urban backyard was teeming with House Finches, Northern Cardinals, grackles, and chickadees this summer. And then, without any warning, poof. Gone. Even the abundant House Sparrows vanished into thin air. It was like some mysterious bird-sucking vortex hovered over my yard and whisked all the birds away overnight. But of course, that's not what happened.
Did the birds finally get tired of my ridiculously adorable dog stalking them while they perched on the fence? Or did our neighbor's fat orange tabby cat scare them off? (Sure, I love kitties, but please, please keep them indoors.) Could be. When birds sense a predator on their turf, they will split. Last spring, the songbirds disappeared when a pair of Cooper's Hawks took up residence in a nearby tree. But once the hawks left their territory, the regular birds returned.
Another possibility is that they found a better food source elsewhere. I didn't have feeders out this summer, but plenty of birds hung around to scavenge for insects and stray seeds in my garden. Earlier in the summer, chickadees chattered to each other in the neighbor's big box elder, hunting for bugs. Grackles pecked at the front lawn, and robins tugged at the biggest worms I'd ever seen. But food doesn't stick around forever. If there's a better meal the next block over, the birds will find it. It's like knowing which of your friends' moms made the best meals and always trying to stick around long enough to get invited over to dinner. Birds know that trick, too, only they don't wait for an invitation.
But what about folks who seem to have the perfect bird habitats? They put out feeders, birdbaths or misters, don't have predator issues, and have loads of appropriate vegetation and shelter. What's happening when their resident birds disappear? Well, sometimes it's simply that birds move around. Populations fluctuate, and as much as we'd love to always have goldfinches or cardinals in our yards, it's unrealistic to expect them to stay put all year long.
Weather plays a big role in the movement of birds. It got very, very dry here in Wisconsin this summer, and it seemed like everything disappeared for a while -- except for the cicadas humming high in the trees. If there's no water, food, or shelter, birds will move along until they find appropriate habitat. In the winter, American Robins, sparrows, blackbirds, and other species will sometimes vanish after big snow or ice storms. These "hard-weather migrants" move in response to harsh weather. "Hard-weather migrants usually move in conjunction with cold fronts," Paul Kerlinger wrote in our February 2000 issue. And with fall on its way, I suspect the cool masses of air pushing into the Midwest are sending signals to even the year-round birds.
Some birds, even our regular backyard visitors, move around in response to seasonal changes. During the fall and winter months, robins will leave their nesting territory and travel in flocks to find more food. House Finches, too, tend to move south in the summer and north in the winter, and don't necessarily frequent the same winter spots. "House Finches show a strong tendency to be in the same general area from summer to summer. However, the tendency to be in the same area from winter to winter is much weaker," says Thomas Hamilton in North American Bird Bander. So while they might not travel thousands of miles, some birds do go on "mini-migrations" when the seasons change.
All that said, it's also worth mentioning the possibility of climate change affecting bird populations. Do I think it's the reason why the finches disappeared from my yard a few weeks ago? No. At least not for now. But scientists suggest that climate changes are affecting when birds migrate, when they lay eggs, and the health of the habitats they frequent. So while it might not be evident in my yard right now, I can't ignore the possibility. – J.E.