Sunday, July 3, 2011
Rodents vs. Birds
Transcript of July 1, 2011 For the Birds
Last week when I was staying in a lovely little cabin in northern Wisconsin, I was brushing my teeth one evening before bed when I noticed a young white-footed deer mouse in my shower stall— there was an opening in the wall where it joined the ceiling, and he’d apparently been crawling around up there until he suddenly dropped down. The shower door was closed so the little guy couldn’t get out on his own. I didn’t want him loose in the cabin, and didn’t want to hurt him, so while he was away from the door I slid it open, put in a wastebasket on its side, closed the door again, and then sat waiting patiently, and then impatiently, for the little guy to finally go into the wastebasket. The mouse was very suspicious, a quality that may serve it well in the long run but was most inconvenient for me, because although this was a small shower stall, he steered clear of the wastebasket for three full hours. Finally, he tentatively entered the wastebasket and I snatched it up, brought it out the door, and set it down on its side on the forest floor. He took a minute or two to sniff before finally leaving the wastebasket and scurrying off into the darkness. Not a minute later, a Barred Owl started hooting. I went to bed thinking about how tricky it is negotiating life on a planet where predation is such a widespread phenomenon, and hoping my little mouse would beat the odds and eke out a long and prosperous existence.
Then this week I read a newly-published paper in the Journal of Animal Ecology, about a study of how two of my favorite forest birds, Veeries and Ovenbirds, elude mammalian predators by avoiding nesting in places where they vocalize. When the researchers set out speakers playing the calls of chipmunks, both Veeries and Ovenbirds avoided a wide area around the speakers. If the speakers were playing calls of innocuous frogs, the birds didn’t show this avoidance of the speakers. White-footed deer mice don’t make much noise, so the authors didn’t play sounds of them, but in their discussion they mentioned that deer mice feed on the eggs and nestlings of these ground-nesting birds, too. Rodents actually eat eggs and nestlings both in trees and on the ground, though ground-nesting birds suffer far more from it. And I suspect smaller birds are more helpless to stop a chipmunk or mouse than larger birds are—the study found that Ovenbirds kept their nests twice as far from the speakers than the larger Veeries did.
People have long known that birds respond to their own species’ vocalizations—it’s cool that people are finally noticing that they also hear and recognize the sounds made by other species, and are able to use a wide variety of cues in their environment to make important life decisions. A lot of people still seem to think that bird intelligence is extremely limited and that most of their behaviors are based strictly on instinct, but in reality, they are far more intelligent and adaptable than we give them credit for.
So finding yet more confirmation of my beliefs about bird intelligence and adaptability was a big take home message of the study. But the other message was an added awareness of how hard mice, chipmunks, and other rodents are on birds. I still find them adorable, and can hardly judge them harshly after eating a breakfast of eggs and looking forward to a dinner of barbecued chicken. But somehow releasing that little mouse, to eat baby birds until it’s in turn one day eaten by an owl, seems more fraught with complexity than it did at 1 a.m. when I just wanted to get the little guy out of my cabin.
Laura Erickson at 6:52 AM