AUTUMN 2007/VOLUME 21, NUMBER 4
Yard Cats and Birds
Citizen-science data show cats kill a diversity of backyard birds
Studying birdlife in inaccessible locations doesn't always require an expedition to a remote rainforest. One of the most difficult places for ornithologists to study is literally right in our own backyards: urban and suburban landscapes. Although backyards are not physically impenetrable, private residential areas are often inaccessible to scientists wishing to better understand these areas as habitat for birds. For the last two years, several hundred citizen-science participants have given us a glimpse into urban birdlife through My Yard Counts, a pilot study examining the lives of birds in these areas.
Besides the lack of suitable habitat for birds, urban areas present unique threats to birds, such as window strikes and pet cats. According to the American Bird Conservancy, cats may kill hundreds of millions of birds, small mammals, reptiles, and amphibians each year. However, little is known about which bird species are affected most, or about the extent to which people can influence the level of cat predation in their yard. Tessa Murante completed her undergraduate honors thesis in May 2007, working with our research team at the Cornell Lab of Ornithology to analyze data from My Yard Counts. She found a surprising diversity of bird species killed by cats in residential areas (Figure 1 below).
Although these data are preliminary, they provide much-needed information about predation by pet cats in residential areas. In previous studies, researchers have concluded that cats are opportunistic, preying on most common species. However, most evidence of cat predation on birds is based on studies of feral rather than pet cats and on islands rather than continents. These studies may not tell us much about how to conserve residential bird communities for several reasons. Unlike pet cats, feral cats may rely on hunting for most, if not all, of their nutritional needs. They may rely mostly on birds for prey since islands often have fewer mammals. Additionally, birds on islands are easy targets for introduced cats, because they often lack the instincts and behaviors to escape predators. Finally, bird populations as a whole are more vulnerable on islands because their populations tend to be small to begin with.
Of all birds reported killed by cats in our study, most have stable or increasing populations, and only one species (Eastern Towhee) is of conservation concern. Evaluating the impact of cat predation in residential settings should provide useful insights into what we need to do to help keep common birds common. A better understanding of the hunting patterns of pet cats will help determine whether certain species, or species with certain traits, are more susceptible than others to cat predation. With Tessa, we are also investigating whether people can influence the level of cat predation in their yard—not an easy task when neighborhood cats roam freely.
We continue to have many questions about the role that residential areas can play in conserving avian populations. In particular, we still have much to learn about the threats to bird survival and how that alters population dynamics. In the meantime, you can find out how to limit cat predation by visiting the Cats Indoors web site of the American Bird Conservancy at www.abcbirds.org/cats. In addition to taking steps in your own yard, consider printing out one of the web site's brochures to give to your neighbors about why they should keep cats indoors.
Caren Cooper is a research associate in the Lab's Bird Population Studies and Citizen Science programs.
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