Suburban Birds

As everyone in animal sheltering and rescue knows, there is a very complicated debate swirling around the issue of whether outdoor cats are significant predators on wild birds. The No Kill movement is fortunate to have Peter Wolf, who writes the blog Vox Felina, to help elucidate the scientific issues in this debate.

Although the debate is complicated, one thing is certainly true, and that is that if bird populations are flourishing then cat predation cannot be all that terrible. A recently published book indicates that in at least one important environment – green suburbs – birds are flourishing in spite of the presence of lots of cats.

The book is Welcome to Subirdia, by John M. Marzluff, who is a professor of wildlife at the University of Washington. Since I’m not an expert on bird ecology, I’m relying on a review of the book that appeared in the November 20, 2014, issue of The New York Review of Books. The review is “It’s Time to Live With the Birds,” by Robert O. Paxton, who is an emeritus professor of social sciences at Columbia and a former president of the Linnaean Society of New York.

The surprising thing about suburbs is that they not only have lots of birds but they have lots of bird species. One thing that concerns conservationists is when a few species of birds – such as starlings, house sparrows, and pigeons – predominate. That is not true in the suburbs, and one example from Marzluff’s book that Paxton cites is the finding that Central Park in the heart of New York City has a greater number of bird species than Yellowstone.

Not all suburbs qualify as suitable habitat for a diverse bird population. Marzluff found that a suburb needs to have about 30% of its landscape planted in natural vegetation. It is actually the variety of habitat, including parks, trees, gardens, ponds, and even lawns (if they are messy), that allows such a variety of bird species to flourish. Suburbia, unlike urban cores or farms, supports diversity of bird species by its diversity of micro-habitats.

Marzluff’s thesis is much more complex than this short summary suggests, and neither he nor Paxton sees the suburban habitat as a solution to the great extinction going on. The interesting thing about his thesis for the bird-cat debate, though, is simply the fact that birds can flourish in an environment that is full of cats as long as the environment otherwise meets the birds’ needs for food, shelter, and a place to raise their young.

One of Marzluff’s recommendations for encouraging bird numbers is to keep cats indoors. That may be a good recommendation, but the fact is that we’ve had cats in the United States at least since the early immigrants came over from Europe, and there has never yet been a time when everyone kept their cats indoors. And feral cats, of course, do not live in suburban houses. The recommendation is also a bit puzzling in the face of Marzluff’s own finding that birds are flourishing in a cat-rich environment. If suburbs have a greater variety of bird species than our large national parks, then it is very hard to argue that suburban cats are bad for bird conservation.