At first glance, you might expect nothing but benefits to come from feeding wild birds. Finding enough to eat is a major preoccupation for birds, especially in winter. So wouldn’t it make sense that feeding stations well stocked with seeds would make life easier for our feathered neighbors?
In fact, though, controversy about bird-feeding prevails, and a good deal of research has been done to measure the effects of this activity. The practice, though it surely makes it easier for humans to enjoy the company of birds, can have surprising unintended consequences. But by understanding some of the dynamics put in motion by a bird feeder, you can make an informed decision on whether or how to feed wild birds.
First, it’s worth noting that many species of birds, both native and those introduced here, will visit feeders, and the more varied your offerings, the more species of birds are likely to show up. Under some conditions — for instance, a severe cold snap after a heavy snowfall — a stocked feeding station probably does improve the survival rate of local songbirds.
But it improves survival by less than one might expect: birds smart enough to survive to maturity are amazingly resourceful at surviving adversity. And there is very little evidence that feeding stations improve survival under normal conditions. A feeder tends to be just one source of food for a wild bird, and if the feeder is removed, most species are perfectly capable of foraging adequately on more natural sources of food. So the main beneficiary of a bird feeder probably isn’t the birds at all, but rather the humans who enjoy the chance to see birds reliably at close range.
Moreover, as a routine practice, bird-feeding exposes birds to several risks that can’t be completely controlled. A bird feeder is a much more concentrated food supply than birds ever experience in nature; as a result, it distorts the behavior of birds and exaggerates some of the results of their normal actions.
Take disease, for instance. Feeders bring birds into intimate and frequent contact with each other, creating opportunities for disease transmission. House finches, famously, acquire a lethal form of eye disease from feeders; many species are known to get Salmonella poisoning from eating seed contaminated by the droppings of other birds.
Then there are predators. Outdoor or feral cats can wreak havoc around a bird feeder, lurking under a bush and picking off unwary visitors. And several species of hawks take advantage of the songbirds that concentrate around a feeding station. In settled areas, falcons or Coopers’s hawks largely spend their days working a circuit of feeding stations they’ve located, blasting in on a low-level pass and picking off a startled songbird as the flock scatters. This works out well for the hawk, which may be eating the same number of birds as it otherwise would, but with less time and effort. But it may mean that the local songbirds are at unnaturally high risk for being eaten.
Meanwhile, collisions with windows, which birds often perceive as open spaces rather than solid surfaces, are a major source of mortality among songbirds. By attracting large numbers of birds into the proximity of your houses, you’re increasing the likelihood that one will break its neck on your sliding door.
More subtly, a bird feeder benefits some species more than others, and depending on the surroundings, the species receiving the largest boost may not be the most desirable birds. For example, most heavily settled areas support large flocks of house sparrows, which descend voraciously on feeders. During the breeding season, the hordes of house sparrows supported by feeders compete aggressively for nesting cavities with native chickadees, swallows, bluebirds, and woodpeckers. So bird feeding can have an indirect impact on native bird breeding success.
All of these effects, positive and negative, interact in ways that are too complex for broad generalities. You need to look at your specific situation – where you live, what birds are around, and how much effort you can put into maintaining a feeding station.
If you decide to feed birds, here are a few rules that may help you do more good than harm.
Position feeders a few yards from dense cover, to make it hard for a cat to pounce from concealment an to provide birds with an accessible escape route from the inevitable Cooper’s hawk. Avoid millet-heavy seed mixes, which attract mainly non-native species; sunflower seeds still in the shell, thistle seed, and suet seem likely to attract the most desirable mix of native species. Keep your cat inside. Clean the feeders regularly, including sweeping up dropped seed from the ground.
I’m all in favor of appreciating birds, and my personal opinion is that bird-feeding rarely has negative impacts that rise to the level of ecological significance. But the practice injects an unnatural and potentially risky element into the lives of your little friends. You owe them some attention to detail.