The Voltage Gate

It has been claimed in the past that birdfeeders were bad for the environment, and now a couple of researchers are looking into published literature on whether or not birdfeeders significantly disrupt the ecology and future evolution of birds.

The PR from SD is basically highlights of the researchers' survey, including indications that birds may get "trapped" in inhospitable areas by the surplus of food or that birdfeeders can disrupt a bird's natural breeding/feeding cycle throughout the year.

This review seems to be a jumping off point for more research:

"Changing the natural dynamics of food supply at such a large scale represents a major intervention in the ecology of birds," says Robb. "But we have a remarkably limited understanding of the impacts of bird feeding."

There have been relatively few studies conducted which incorporate urban and suburban yards, for example, and very few studies have run for more than one or two years or considered more than one species. Robb and Bearhop plan to continue their investigations at field sites in Northern Ireland and Cornwall.

"It seems highly likely that natural selection is being disrupted," Robb says.

According to the review, almost 50 percent of the US and 75 percent of the UK provide food for birds in some capacity.

From what I've heard from ornithologists, it's far more useful to provide fresh water for birds than food, as in most areas, food from natural sources is relatively easy to come by. But then again, we don't really feed the birds to provide sustenance entirely; it's the best way to see what species live in or are migrating through your area.