Wild Side : To feed or not to feed?
Vineyarders love to watch birds, and a lot of that watching goes on at feeding stations. Indeed, observant feeder-watchers deserve much of the credit for Martha's Vineyard's reputation as a magnet for rarities: many of the vagrant songbirds recorded here are spotted among flocks of "the usual suspects" at feeders.
But there is no such thing as a free lunch, and that goes for birds, as well. While doling out millet and sunflower seeds to local birds may seem like an unimpeachable act of kindness, feeding wild birds actually has surprisingly complex and far-reaching ecological effects. Not all of them are good. In the world of ornithology, a small but persistent minority actively opposes bird feeding.
Some negative effects stem from the tendency of birds to concentrate around feeding stations. The house finch, for example, an introduced species in the eastern U.S., lives almost exclusively in settled areas and appears to depend heavily on bird seed. A bird feeder might entice several house finches to sit, almost touching, for an hour or more as they shuck sunflower seeds. Such prolonged chumminess would be rare under natural conditions, and there is ample evidence that such proximity facilitates the spread of disease among finches. Indeed, it is beginning to look like disease (especially an eye disease to which finches are especially prone) effectively caps the population size and density this species can achieve in our region.
Concentrations of birds at feeders also attract predators. Sometimes, this furnishes added excitement for the observer: a Cooper's hawk or a merlin sprinting out of nowhere to nail a sparrow is a thrilling site, even if one sympathizes with the victim. The few studies that have been done on the subject suggest that feeding stations don't actually result in more birds getting killed. But under some circumstances, such as when bushes allow domestic cats to lurk within leaping distance of a feeder, an intended act of kindness may in fact lure birds into unnecessary danger.
In addition to the direct effects on the species we feed, bird-feeding causes indirect effects on other birds. If feeder food helps more individuals of a species survive the winter, more individuals will enter the breeding season, and on average they'll be in better condition. The result is more prolific breeding, and any birds that species competes with are in for a struggle. Moreover, when feeding boosts the survival of an omnivorous species like the blue jay, the added jays will eat additional eggs and young come spring, when this versatile forager shifts into nest-raiding mode. The result is reduced breeding success among migrant birds such as orioles and warblers, many of which are already in decline for other reasons.
While I hate to assign values to different species, some of the birds that flourish year-round in densely settled areas (and therefore benefit most from feeders) have little to recommend them. On the Vineyard as elsewhere, non-native species like the house sparrow and European starling typically associate closely with human activity. But the success of these two introduced species comes largely at the expense of native species, through competition for food or nest sites. Feeding birds, then, may sometimes alter the local species mix in an undesirable way, favoring prolific generalists over less common native birds.
So, should you feed birds or not? If you expect a simple answer, you're reading the wrong columnist. But I can tell you that I do feed birds, largely because the ability to observe birds closely and frequently greatly enriches my life. I also feel pretty sure that I'm doing birds, or at least individual birds, a favor, enhancing their odds of surviving the winter. (Several studies support this belief.) Most winters, my yard attracts stable groups of white-throated and song sparrows; often, distinctive markings let me keep track of individual birds. And it's clear that, most years, nearly all of "my" sparrows survive the winter.
But in terms of the broader ecological effects of feeding birds, I'm less comfortable. One study asserts that 43 percent of Americans feed wild birds, spending $2.5 billion annually in the process. That adds up to a huge deployment of resources that benefit some species - winter residents with a tolerance for human activity - much more than others. In effect, feeding birds tilts the ecological playing field.
If you allow yourself the pleasure of attracting birds to your home, minimize the negative impacts by keeping feeders clean and siting them amid a buffer of open space, so birds can dodge incoming attackers. Meanwhile, do what you can to help protect areas where wild species can live out their lives without the unnatural influence of human handouts. This plan gives the birds and people the best of both worlds.