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Region's wild animals migrate to urban environments

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By Mark Browning
Sunday, Nov. 2, 2008
 

Recently, on a cool, sunny morning within view of downtown Pittsburgh, I was taking out the garbage before work when I spotted something in my neighbor's backyard that made me stop and take a breath.

A large, gray cat -- twice the size of a housecat -- was loping across the lawn. Something I did cause the animal to notice me, and it became a blur of powerful leaps. I ran down the path to catch a glimpse of it as it sped through the woods. The animal's heavy body, large ears and, most of all, its bobbed tail made me realize I was seeing a bobcat. I have enjoyed the thrill of seeing bobcats on just two other occasions, bothin Florida wilderness. To see one so close to a city seemed almost surreal.

Not long before that, I had listened to a group of coyotes call within a stone's throw of my deck. And a week before seeing the bobcat, I watched a red fox stroll through my front yard.

The dramatic migration of wildlife into the city of Pittsburgh tells a tale of successful conservation and animal adaptation. Forty years ago, there hardly was a deer or turkey within city limits.

Today, they literally walk in groups up city streets. Other forms of wildlife have followed.

As someone once said: Nature abhors a vacuum.

With the high numbers of prey come predators. This includes bald eagles, once an endangered species; ravens, more often associated with the northern mountains; coyotes that have continued their spread east and, yes, even bobcats.

The ravens came last winter. Despite what many think, ravens aren't just large crows. They are more eagle-like than crow-like, with powerful beaks that can rip through a deer hide and 4-foot wingspans that rival those of red-tailed hawks.

When you see one, you know that you are seeing a different creature. Their calls are different, too -- not caws, but deep, guttural croaks and grunts. The ravens seemed to follow the Allegheny River south into Pittsburgh. They were seen through the winter in Aspinwall and Highland Park, perching on light poles over the bridges and flapping heavily along the shore.

The raven population, thickest in Pennsylvania's northcentral mountains, is not that robust. So why were we seeing them•

"Ravens wander around quite a bit, especially the juveniles," says Bernd Heinrich, author of books including "The Mind of the Raven" and professor of zoology at the University of Vermont. "They often show up in cities, particularly in winter."

Severe weather in the mountains could prompt the juveniles to move south, Heinrich says, and, importantly, the dense populations of game in the city might lure these carrion-eating birds. There is every expectation that we will see ravens again this winter.

Bald eagles have been visiting Pittsburgh during the past few years. Last year, two adults and a juvenile wintered along the Allegheny.

Their presence is testimony to a successful conservation effort. In 1980, only three pairs of eagles nested in the state, but between 1983 and 1989, the Pennsylvania Game Commission released numerous young eagles. Today, the state has more than 100 breeding pairs.

"Once, it was a very rare sight in Pittsburgh, but now in winter, one might see a bald eagle any day of the week," says Brian Shema, director of conservation for the Audubon Society of Western Pennsylvania. "When their feeding grounds along the Pymatuning and Geneva Lake shores freeze, they follow the rivers southward and find better hunting along the open waters, where they can find fish and ducks."

Beth Fife, wildlife conservation officer for the Pennsylvania Game Commission in this region, sees the presence of such animals as evidence that the rivers are cleaner. She cites river otters as an example.

"Since reintroduction," she says, "otters are expanding up and down the three rivers, and their presence is an excellent indicator of healthy fish populations."

Otters, secretive animals that are best seen at dusk and dawn, have been observed along rivers near Harmar and and Peters.

Fife also cites beaver that are denning along the rivers.

"Local beaver populations are very healthy," she says. "They've adapted to the rivers by building bank dens vs. log dens and are expanding up and down the rivers, as well."

Beavers, which are strict vegetarians, often are seen near Neville Island, not far from Downtown.

One animal that does worry Fife is the coyote, whose populations, she says, are increasing. In 2005, hunters and trappers harvested more than 20,000 coyotes statewide. She even has record of one in downtown Pittsburgh.

"They are highly adaptive," she says, "able to sleep under a shed or a porch while people don't know they are there. They like to eat domestic cats and, of course, there is the danger of distemper and rabies. But on a positive note, they can provide a check to deer populations."

Surprisingly, Fife says, "The Pittsburgh region has a higher density of wildlife than any other in Pennsylvania."

The truth is, the city offers a lot of advantages to animals:

• Hunting is not common in the city.

• Until recently, there were few predators.

• Humans tend to create a lot of border areas -- garden-like environments where the sun shines through enough to create a lot of second growth and food.

• Many residents put out feeders.

• Most of all, Pittsburgh is geographically unique -- built on steep hills and ravines that could not be developed.

What enabled wild animals to shed their instinctual fear of humans• At least two types of acclimation are occurring with wild animals in urban areast.

The first is individual behavioral acclimation. As these animals, particularly when young, are exposed to the fringes of human settlement, they become accustomed to the sound of motors, slamming doors and screaming children.

The second type of acclimation is genetic. Having worked in zoos for a long time, I have personally witnessed the range of psychologies in a single group of animals born to the same parents. There are shy ones and aggressive ones, retiring ones and determined ones.

Just as genes provide an array of physical traits that give the species an advantage under different conditions, the genes provide an array of dispositions. Given the motive -- and an untapped wealth of food is a great one -- aggressive, determined animals might find an easier living in a city neighborhood. When that happens, bold animals encounter other bold animals, mate and create animals more likely to have their own dispositions.

This is to not to say that urban development and the spread of suburbs has been good for all wildlife. In fact, development has devastated wetlands and grasslands and all of the species associated with those habitats. But Pittsburgh provides a great example of the resilience of wildlife.

By fortune of its deep ravines, steep hills and winding rivers, the Pittsburgh region also provides a perfect example of why wildlife corridors -- swaths of undeveloped land that allow animals freedom of movement -- are vital to healthy ecosystems. Environmental conditions change, and animal populations cannot be expected to remain in designated areas, but instead must have ways to move in response to geographical and population changes.

Such corridors, linking national parks and other wilderness areas, have been proposed for decades by biologists. Who would have known Pittsburgh would become testimony to such thinking•

And Pittsburghers, keep your eyes open. Eagles, ravens, otters, coyote and bobcats, even when glimpsed for a moment, can provide and exciting experience.

Mark Browning is a zoologist for the Pittsburgh Zoo and trains sea lions and performs field research on owls.

 

 
 


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