Do Birds Prefer Suburbia?
A new book has led to some confusion as to whether suburbs are the best bird habitat. Here are 7 reasons why nature still trumps sprawl.
Are there birds in suburbia? Sure. Every serious birder has noticed that. On an Audubon Christmas Bird Count, for example, when things get slow out in the woods, we often head into the suburbs to check out the gardens and parks. There, the varied habitat often produces bird species that we didn't find out "in the wild."
John Marzluff, a professor of wildlife science at the University of Washington, has done more than just notice. He has documented this diversity of suburban birds through careful studies, and has authored several papers on the subject. He even coined a term for bird-rich suburbs: "Subirdia." His book Welcome to Subirdia, slated for publication in September, will bring his ideas to a wider audience.
Even before publication, Marzluff's book is drawing attention. On July 28, science writer Robert Krulwich wrote about it on the NPR blog: "Where The Birds Are Is Not Where You'd Think." Krulwich was clearly intrigued by the comparison of bird diversity in city centers, suburban areas, and wild forests, and the fact that "the suburbs, shockingly, win," as he writes. Further on, he concludes, "wild and wide open spaces, apparently, offer no special advantages."
Within hours of Krulwich's post's appearance, social media lit up with birders questioning it. Did the NPR piece accurately reflect the focus of the research? Was the study actually suggesting that suburban sprawl is good for birdlife?
There's no faulting the science behind Marzluff's findings. He and his students have more than a decade of data from an extensive series of points around Seattle, and the pattern is clear: The variety of birdlife is lowest in the city center, increases to a maximum in certain suburban areas, and then declines somewhat toward the undisturbed forest. More kinds of birds live in those suburbs than in the natural habitat.
So suburbs are the best bird habitats, and we can forget about trying to protect natural ecosystems, right? Wrong. That's not what the research really suggests. After speaking with Marzluff and taking an early look at the book, I can confirm the situation is not so simple.
Here are seven reasons why natural habitats are still better for birds than suburbs:
1. Seattle is special. The pattern of more bird species in the suburbs than in nearby wild areas has been documented, to some extent, around several temperate-zone cities. But it may be a lot more noticeable around Seattle, where much of the surrounding land is covered with unbroken coniferous forest--often a very slow birding habitat.
2. Not all suburbs are created equal. Square miles of concrete and mowed lawns support few bird species. Marzluff found peak bird diversity in suburbs that had at least 30 percent natural cover: parks, streams, greenbelts, undeveloped lots holding patches of the original native forest. With less native cover, diversity levels dropped.
3. Suburbs mimic aspects of the best natural habitats. The most bird-rich suburbs had a wide variety of native and ornamental plantings, creating a high diversity of plant life, as well as bird feeders, bird houses, and artificial ponds. In the wild, we often find the most bird species in "edge" situations, where one habitat meets another. Suburban habitat is like an endless series of edges. So there's potential for more different birds to find a niche there.
4. Some birds have adapted to urban life, but others can't. Long-term studies in London, for example, have shown that the diversity of birds living in certain parks has increased. But some species, termed "avoiders," seem unable to adapt to life in developed areas. In North America, forest birds such as Wood Thrush, Ovenbird, and Red-eyed Vireo are in this category. Many bird species will survive only if they have sufficient sanctuaries of natural habitat.
5.Tropical regions still dominate. The pattern of highest diversity in the suburbs breaks down completely in tropical regions. No suburban habitat can approach the number of bird species living in tropical forest.
6. Local diversity isn't everything. It would be wrong to measure a bird habitat's value only by the number of species living there. Some unique habitats support rare and specialized birds that wouldn't survive anywhere else. For example, a marsh hosting Yellow Rails and Le Conte's Sparrows is more significant, from a conservation standpoint, than a suburban neighborhood filled with starlings and robins, even if the latter might have more total species.
7. Suburbs aren't as good for other wildlife. As detailed in a chapter in Marzluff's forthcoming book, other life forms beyond birds don't necessarily fare so well in the suburbs. Many native mammals, reptiles, and amphibians disappear from developed areas, and fish and other aquatic creatures often decline in urban and suburban streams. So the birds, mobile and adaptable, may not reflect what suburbia is doing to other creatures.
So is suburbia--or, as the book title has it, subirdia--good or bad for birds? Well, it's complicated, and no simple answer will suffice. Surprising numbers of species thrive there. Many others don't, and probably never will. But an essential point, unmentioned in the NPR story but central to Marzluff's book, is that we humans can take a wide range of actions to make the suburbs more livable for birds, for other native wildlife, and ultimately for ourselves. This includes maintaining diverse natural cover within suburbs.
While some aspects of the research may lend themselves to a gee-whiz story about birdy 'burbs, such a light treatment of the subject may mislead people into thinking their suburban sprawl is okay after all. In reality, Marzluff's book presents a more nuanced argument, and most importantly presents a potential action plan for how to make things better.