A team of researchers set out to investigate the ecological impacts of bird feeders. Bird feeding is popular among the public but may occasionally put birds at risk for increased predation. The details are in a paper that was just published in the journal The Condor: Ornithological Applications.
More than 50 million Americans use bird feeders and many of these individuals are passionate about their hobby. Bird feeders attract pretty birds and other critters to the yard, providing a relaxing experience. Some people also believe that the feeders help birds, especially in winter when food is scarce. Scientists have raised concerns about feeding wildlife and the ecological impacts are poorly understood.
Researchers from Ohio State University conducted a large bird feeding study in Ohio over a period of four years. They studied nests of American robins (Turdus migratorius) and northern cardinals (Cardinalis cardinalis), both common songbird species found throughout North America. The team observed nests in seven residential neighborhoods and tracked factors such as survival rates, predator density, competition among other birds, and nesting success. The team used the help of citizen scientists to gather data since their study was mostly conducted on private property.
The researchers found that factors such as risk of predation and nesting success varied significantly from neighborhood to neighborhood. Overall, very few obvious patterns emerged and the study became more complicated than expected. One constant was the presence of crows and their relatives near yards with bird feeders. These species are known to prey on the eggs and nestlings of songbirds. However, further data analysis showed that crow density didn’t have a serious effect on most nests. An exception was a neighborhood with an unusually large number of bird feeders. In that specific neighborhood, the high crow density resulted in increased predation on American robin nests. This points to a possible problem but the researchers acknowledged that more data was needed.
The team’s findings show that the effects of bird feeding on the local ecosystem are more complicated than previously thought. In some neighborhoods, bird feeding could put songbird nests at risk of predation by crows. Much more data is needed, however, and there were no noticeable effects at the other research sites. The authors emphasize the need for more research in this area.
Malpass et al. Species-dependent effects of bird feeders on nest predators and nest survival of urban American Robins and Northern Cardinals. The Condor: Ornithological Applications (2016).