Monday, 4 August 2014

Where the birds are - a recent American debate

Where The Birds Are Is Not Where You'd Think

and Kenn Kaufman's rebuttal/explanation

Where The Birds Are Is Not Where You'd Think
July 28, 201412:19 PM ET
This is a trick question. Where would you expect to find the greatest variety of birds?

Downtown, in a city?

Or far, far from downtown — in the fields, forests, mountains, where people are scarce?

Or in the suburbs? In backyards, lawns, parking lots and playing fields?

Not the city, right?

"Everything I have learned as a conservation biologist tells me cities are bad for biodiversity," writes John Marzluff, of the University of Washington.

We all know this. Anyone who goes to downtown Chicago, Toronto, Seattle, LA, Boston or New York will see the same five birds over and over: sparrows, starlings, mallards (ducks), geese and, of course, street pigeons. Same goes for downtowns in Europe, Asia and South America. These five bird types are always there, always the same, never surprising. Rather than yawn, scientists have a category for this: "biotically homogenous." We've made cities. They've moved in.

A Seattle Experiment

But now comes a surprise. Actually, several surprises. When Marzluff and his students went to downtown Seattle to count bird species, within the first 10 to 15 minutes they spotted pigeons, finches, sparrows, crows and an occasional hummingbird. Their count was 10 to 15 different kinds of birds — not many, but they expected that.

When they went the other way (to the far edge of the metropolitan area near the Cascade Mountains, where there is mostly forest, protected parks, reservoirs, and humans are sparse), in the first 10 to 15 minutes, they found a very different set of birds (woodpeckers, wrens, warblers, chickadees). In all, 20 different species — more, but not many more than downtown.

Then they went to the in-between zone, the Seattle suburbs, where they expected an in-between count, something like 12 different kinds of birds. But that's not what happened.

"We were astonished," Marzluff writes. The suburban count (again in the first 10 minutes) was "30 or more species," says Marzluff, some from downtown, some from the mountains, but also spectacularly new samples of "violet-green swallows, willow flycatchers, killdeer, orange crowned warblers, American goldfinches, and Bewick's wrens ... [plus a few] white crowned sparrows." The suburbs produced, by far, the most biologically diverse collection of birds.


What? This region that's all sprawl, a hodgepodge of strip malls, yards, highways, parking lots, hedges, fences, is "a mecca for birds"? More than a forest? No way, thought Marzluff. So he counted again. Then again. And after checking and compiling "more than 100 locations in and around Seattle," he writes, he and his team discovered "a consistent, but unexpected relationship between the intensity of development and bird diversity."

To his great surprise, Marzluff concluded that the "greatest diversity was not in the most forested setting. Instead, bird diversity rose quickly from the city center to the suburbs and then dropped again in the extensive forest that eases Seattle into the high Cascades."

He had just discovered, he writes, "subirdia." And that's the name of his forthcoming book, due this fall, called Welcome to Subirdia.

But Why?

So what have suburbs got that forests don't? Suburbs, he says, offer a wide range of artificially designed garden habitats, providing a smorgasbord of nuts, fruits, seeds, insects and ponds, in dense concentrations. Because they are rich with different kinds of bird food, suburbs are rich with different kinds of birds.

In Leicester, England, one survey found 422 different plant species in a single garden. Another census of 61 private yards in Britain found 1,166 vascular plants, 80 different lichens, 68 varieties of moss.

But let's not get crazy about this: Suburbs are not the birdiest zones on Earth. Any patch of tropical forest, with its dazzling populations of plant and animal life, will trump a garden-rich suburb. But if you are comparing suburban bird diversity with temperate wild spaces — say the Cascades, the Smokies or the Adirondacks — the suburbs, shockingly, win.

Birds And 'Burbs

And not just in Seattle. Marzluff writes that "throughout Britain, in deciduous woodlands of California and Ohio, grasslands of Arizona, forests of Japan, and shrublands of Australia, moderate levels of urbanization also provide an abundance of various resources that increases the number of bird species beyond that found in either wilder, or more densely populated settings."

So, like 40 percent of America's humans, a big hunk of America's bird species have chosen to live the suburban life. It's a bird boom, I'm surprised to say, I had never noticed.

In his forthcoming book, Welcome to Subirdia (to be released in September), Marzluff drops one last bomb — "a real stunner," he says. Every March, he spends a few days in Yellowstone National Park, up on the northern edge. That's a 2.2 million-acre expanse of wild space — very, very big. In 2013, he counted 26 bird species there.

Then he got on a plane and headed east to New York City, and found himself along Sixth Avenue, where he saw the usual "house sparrows, European starlings, and rock pigeons." And when he reached Central Park, he entered and found some mallards and the geese, so the usual urban bird quintet was accounted for; but as he walked around, he spotted a cardinal, then a blue jay, then a white-throated sparrow, then a black-crested titmouse, then a Cooper's hawk, then some crows, some blackbirds, three varieties of woodpeckers, wood ducks, cormorants, red-tailed hawks, herons, mourning doves — altogether 31 species. He saw a greater variety of birds in Central Park than he did in Yellowstone. We all know New York attracts exotic people, but birds too? Wild and wide open spaces, apparently, offer no special advantages. "From a bird's perspective," Marzluff writes, "large park[s] created by human hands or by nature are not all that different." Huh.

The rebuttal
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. 

Published: 08/04/2014
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. 

Kenn Kaufman

No comments:

Post a Comment