Researchers study effect of species on area’s ecosystem
By Robert Miller
THE NEWS-TIMES
They’re the wee, cow’rin, tim’rous beasties of the Robert Burns poem — mice, voles, shrews, chipmunks. They skitter through the world, bellies brushing the ground, spreading seeds and carrying the bacteria that causes Lyme disease.
They live to be hunted. We couldn’t live without them.
“They’re a really good indicator of ecosystem health,” said Catherine Burns, who is not a poet, but rather a research biologist who studies small mammals — “squirrels on down,” she said.
Working with WildMetro — an organization dedicated to studying and preserving the flora and fauna that exists and even thrives in the metropolitan New York area, including lower Fairfield County, she’s tracked and trapped hundreds of small mammals, trying to learn the part they play in the greater world. She’s found that while they’re overlooked by most humans, they’re an indispensable part of the environment.
“They’re the main prey for birds and snakes and other larger mammals,” said Burns, who spoke last week in a seminar at Western Connecticut State University in Danbury. “They eat and disperse a lot of seeds.”
But, unlike the bald eagle or the piping plover, they’re anything but endangered. Which means Burns has plenty of subjects to study — in the hundreds of thousands, if not millions.
She can alter their habitats by doing small clear-cuts, then see how changes in their living space change their numbers and the diversity of different small mammal species. She’s learned that meadow voles do better in salt grass marshlands, shrews do better in the forest.
Burns has studied small mammals for more than eight years — first at Yale, where she got her doctoral degree, and since September as director of research at WildMetro. She’s now in charge of WildMetro’s small mammal research, which began in 2004 and has studied sites in 14 urban and suburban parks throughout the region.
She’s learned that small inner-city parks often have higher numbers of small mammals than wilder nature preserves outside city limits, but that the more rural spots have much greater diversity of species.
City mice — in this case, white-footed mice — may have found a niche in small urban parks, where they can survive and where the only hunters they face are feral cats.
In the country, there are different habitats, allowing for more diversity. But, Burns said, there is also a more diverse pack of predators there — coyote, fox, owls, hawks — keeping the numbers of small mammals lower.
She’s looking at the continuum of species, from the omnipresent white-footed mouse to the hard-to-find meadow jumping mouse, which can spring about 3 feet into the air. There are also hard-to-see species, like flying squirrels, that are around only at night.
“They’re as common as gray squirrels or red squirrels in the rural areas,” she said. “But they’re very sensitive to habitat. We almost never see them in the city.”
Burns is beginning to ask questions about Lyme disease and white-footed mice. Researchers now know that black-legged ticks — also known as deer ticks — spread the Lyme disease bacteria to humans. They also know that in their nymphal stage, those ticks first pick up the bacteria from small mammals — primarily white-footed mice.
Burns said one way to study the interplay of the Lyme bacteria and the environment would be to ask if places where there are a lot of wild predators — and presumably, fewer mice — also have lower rates of Lyme disease.
She’s found that where the white-tailed deer herd is thick, there are fewer small mammals — an indication of how much deer alter the landscape.
“This may be due to competition for food,” she said. “Or it may be due to habitat alteration — as deer defoliate the understudy, it’s unsafe for small mammals to live there.”
And she’s developed an undiluted affection for white-footed mice — the most common but also the most gentle of her subjects of study.
“They’re very docile when you handle them,” she said. “A vole will bite you as quickly as it can.”
Rick Ostfeld, a senior scientist at the Institute for Ecosystems Study in Millbrook, N.Y., and a small mammal expert, agrees.
“White-footed mice are nice,” Ostfeld said. “Chipmunks are one of the most vicious animals out there, pound for pound. Red squirrels are even worse.”
Like Burns, Ostfeld said people don’t understand the importance of the rush of small mammals that scurries by, largely unseen.
“We tend to associate importance with size,” said Ostfeld, who has studied the relationship between small mammals and the annual fall of acorns.
“It’s much harder to anthropomorphize something you don’t see, but small mammals are major herbivores in the ecosystem,” said Peter Torchin, a professor of environmental studies at the University of Connecticut, who studies the life cycle of small mammals like lemmings in the tundra of northern Canada.
Torchin said people should think of small mammals as a sort of go-between between the plant world and its larger creatures — they prey on vegetation, then transfer that energy when they get gobbled up by larger predators.
“If you look at biodiversity and the billions of small mammals that there are, they’re very important,” Torchin said.
In New England, Ostfeld said white-footed mice help control the gypsy moth population by eating them in their pupa stage, in the cocoon.
But Ostfeld also said when there is a large number of white-footed mice, the mice feed on the eggs of ground-nesting birds, including the veery and wood thrush. They — along with chipmunks and shrews — also carry the Lyme disease bacteria.
“We want to think of animals as good or bad, but it’s much more complex,” he said. “White-footed mice play a very important part in our ecosystem. We don’t want to be without them. But they also carry Lyme disease.”
Burns said WildMetro plans to continue its small mammal study into the future.
“What we’re doing now in many places is just establishing a baseline of data,” she said.
It also wants to fill in the gaps — to study wildlife across the spectrum of habitats in the metropolitan New York area, rather than simply thinking in terms of “urban, “suburban” and “rural.”
“We also want to look at other animals in the ecosystem — birds, snakes, amphibians,” she said. “We want to see if changes in habitat may lead not to a decrease in numbers but a decrease in the diversity of species.
“Then we may be able to go to towns looking at development issues and say, ‘At this point of development, this is when things start really happening.’”
• Contact Robert Miller
at bmiller@newstimes.com
http://www.newstimeslive.com/news/story.php?id=1029736#tt
The study gives a fresh perspective on global disease by tracking the history, from 1940 to 2004, of the emergence and spread of 335 infectious diseases. The extensive work helps to quantify the effect of well-known risk factors, such as population density, on the probability of a disease taking hold in a given area.