Bird Feeders and Bird Behavior
Location: Outside U.S.
Date: Winter 2011-2012
Do bird feeders alter the evolution of birds? Recently, my family and I put up a bird feeder and many birds come to eat from it. Its winter time here and i still see different types of birds here that I dont usually see this time of year. Can us giving them food disrupt their migration habits, prevent them from mating (do they go south to find mates) and/or disrupt the food chain?
Very interesting questions. Yes, feeders can change the behavior of some birds, including some that will stay north farther or longer into winter than they would without the extra food. I don't believe there is any consensus on how much impact this has on populations in general. It would not likely affect mating. Behavior changes could alter selection and therefore evolution in the very long term. In my opinion it is very unlikely response to feeders will have an important impact on evolution. Many other environmental factors, habitat change that has being gone on for decades, and now climate change, will have a much larger impact than feeding.
According to the Cornell Lab of Ornithology Handbook of Bird Biology (an authoritative reference), based on stomach contents of examined backyard birds, the diet of most backyard birds is surprisingly affected very little by artificial food supplies found at feeders, and their message seems to be "don't worry about your feeders disrupting bird behavior." But even in cases where you might see behavior changes, it still might not affect *evolution* as you mention. For example, birds have an evolutionary urge to migrate, based on day-length mostly, but at least some of it is "cultural", meaning older birds who migrated the previous year guide the younger birds in terms of destination and timing.
I'm not aware of any scientific examples that directly contradict Cornell's claim, but in some US locations Canada Geese overwinter where in the past they didn't, and although it's thought this is mostly because of human eradication of goose predators (rather than food supply changes), our local geese are also seen chomping away at human lawns over winter, so who knows for sure.
Keep in mind also that unless you are an very keen observer, seeing "different" birds at the feeder can be misleading. Several times I thought I was seeing different birds at a feeder (Siskins, Woodpeckers, Grosbeaks, maybe), but once I recognized their calls I realized that they were shy or elusive birds compared to the usual suspects in the backyard, but nevertheless fairly common.
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Update: June 2012