According to the U.S. Fish and Wildlife Service, more than 50 million North Americans feed birds. That’s more than 1 million tons of seed, what scientists call supplementary feeding, provided to birds every year.
According to the most recent State of North America’s Birds report, one-third of all our continent’s bird species need urgent conservation action. More than 400 birds are on the report’s Watch List of species considered most at risk of extinction.
This word cloud portrays population trends from 1966 to 2013 for 98 bird species that use bird feeders at least a moderate amount. Species names in green are increasing in population, yellow have not changed, and red are declining. Larger names are increasing faster than smaller names. The analysis uses Project FeederWatch and Christmas Bird Count data (Soykan et al. 2016. Population trends for North American winter birds based on hierarchical models. Ecosphere 7 (5):e01351). View a larger image.
There are some natural questions that emerge from these facts: Is this massive annual experiment in supplementary feeding affecting our continent’s bird populations? And if so, is feeding birds harmful, or helpful?
There are some clear benefits of feeding birds. We know that some regular feeder visitors, such as Northern Cardinals, are doing very well, because their populations are growing and ranges expanding. But supplementary feeding has also been associated with negative impacts such as disease transmission, deaths from window strikes (when birds fly away from a feeder and into a house), and increased predation pressures (such as Cooper’s Hawks feeding themselves by feasting on feeder birds). Can we reconcile these disparate consequences of bird feeding and determine if feeding is actually harmful on a broad scale?
We decided to put the nearly 30 years of Project FeederWatch data to use to try to answer this question. We made one simple prediction: if feeding birds is harmful, then the species that use feeders the most should be doing the worst, all else being equal. FeederWatch data would tell us how often a species used feeders, and Christmas Bird Count data would give us an independent estimate of how each species was doing over time. We looked at 98 species that use feeders at least a moderate amount and excluded species that rarely visit feeders, because lumping these species would be as logical as comparing chickadees to herons.
We found that species that use bird feeders the most tended to be doing just as well as, or better than, species that use feeders more sporadically. For example, Red-bellied Woodpeckers visit feeders regularly and are thriving, whereas Pinyon Jays visit feeders more sporadically and are showing declines. The feeder species that showed declines seem to be faced with non-feeder–related pressures, such as habitat loss. For Pinyon Jays, the most pressing problem is the destruction of pinyon pine habitat. We are still working to refine this analysis, but the take-home message so far is that species that visit bird feeders a lot tend to be doing very well.
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