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Len Reitsma: At Work with Canada Warblers

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Photo by Len Reitsma.

At 6:00 in the morning, clouds of bloodthirsty mosquitoes hover outside the bug net on Len Reitsma’s head as he hikes through a wet forest to his field-study site. A dull light glints off the dew, causing pine needles to glow and making orb spiderwebs visible. This is the part of science that Reitsma likes best: being out in the forest and learning about nature through observation.

He hears the call of a Canada warbler, which sounds a bit like a high-pitched rendition of a babbling brook. Despite the dense understory of small shrubs and saplings, he quickly sights the bird through his binoculars. He identifies the individual by the color pattern of its leg bands and tracks the singing male as he patrols its territory. At regular intervals, Reitsma records global positioning system waypoints in an effort to map out this male bird’s territory. Next, he locates the nest, a woven cup set into a moss hummock on the ground, and when he checks on its contents, he startles a female incubating four eggs. Then it’s time to move into a new breeding pairs’ territory and repeat similar measurements.

Throughout the morning, several other researchers materialize out of the misty, damp forest, like ghosts in rain suits. They converse briefly with Reitsma, then vanish back into the trees.

For the past six years, every morning from May to July, Reitsma and his research team have been in the forest at sunrise studying Canada warblers. Their goal is to understand why the bird’s populations have been declining steadily throughout their breeding range in the Northeastern United States and Canada. Across northern New England and New York, Canada warbler populations are declining 2.7 percent annually. In New Hampshire, populations have diminished by an average of 4.6 percent per year over the past 40 years.

Little is known about the Canada warbler’s breeding habits, so Reitsma and his crew are attempting to fill in this gap. During the summer, the researchers live at Reitsma’s home in Canaan, New Hampshire, where they are conveniently close to their study sites in the Canaan Town Forest and Bear Pond Natural Areas. Much of the land in these areas is prime Canada warbler habitat: red maple swamp or logged forest with a sufficient number of perch trees.

Reitsma has been a professor of biology at Plymouth State University since 1992 and has been an avid bird watcher since he was a child. At 14, he was given his first pair of binoculars and bird field guide, which he used to identify scarlet tanagers and other birds in the woods and fields around his hometown of Wayne, New Jersey. College didn’t immediately agree with him, so he spent most of the decade after high school working with the family business painting houses. He didn’t complete a degree until, at the age of 29, he finished his studies in biology at William Patterson College. With that degree in hand, he went on to advanced study in biology at Dartmouth College, where he worked with avian biologist Dick Holmes. Since graduate school, he has been teaching college and conducting bird research, including a contract with the U.S. Army to study duck die-offs in Alaska.

Reitsma is equally at home studying birds in the forest as he is teaching in the classroom. In 2005, he received the Distinguished Teacher Award at Plymouth State University. His voice is usually very calm and quiet, though he speaks very intensely on subjects that are important to him. He grows excited about big new ideas, and he likes to involve undergraduates in projects outside the classroom. Each year, several of his students serve as members of the Canada warbler research team.

Over the past six years, Reitsma and his group of researchers have built a picture of how Canada warblers behave and breed. They’ve marked individual warblers and followed them for successive years, learning that the birds in the study area are returning at a rate of about 50 percent to the place they left the previous autumn. More specifically, Reitsma has found that when a male Canada warbler comes back to New Hampshire from South America, it returns to a location that is usually within 32 meters (a little more than 100 feet) of its previous year’s territory. The researchers measure and map habitat characteristics, such as vegetation and insect abundance, to figure out what differentiates high-quality from low-quality habitat for the birds. Another goal is to develop forest management recommendations that could slow the decline of Canada warbler populations across the region.

Songbirds such as Canada warblers had been thought to be fairly monogamous, taking only one mate and having only one nest during a breeding season. Scientists now know, however, that many songbird females produce chicks with genes from multiple fathers, so there is a lot of extra hanky-panky going on. By studying an individual male’s reproductive performance, Reitsma can now pinpoint which birds are the studs of the Canada warbler world, which ones are not, and why.

Reitsma and his crew keep tabs on the warblers from the moment they hatch. They use radio transmitters to track chicks after they have left the nest. Sometimes, what they learn is startling.

“We put a transmitter on a nestling, and then the next day, the transmitter had moved to a place by a big rock,” Reitsma said. “I was tracking [the transmitter’s location], and the signal was moving very short distances underneath a rock. Already, I knew something was up and that the bird wasn’t alive. So the next day, I went back and the radio signal was coming from underneath another big rock. I lifted the rock, and there were six snakes under there, four milk snakes and two garter snakes. I held the antennae and lifted the snakes off, one at a time, until I found the one that had the transmitter in it.”

At the end of his day in the field, Reitsma hikes out of the woods down a winding path and over a wooden bridge, to where he has parked his Volkswagen Jetta (which is modified to run on vegetable oil). It is a five-minute drive to his house from the study site. The rest of his team trickles in around dinnertime, and they gather at the table, excitedly swapping stories about their day, comparing notes, relaxing, and rehydrating. They have just a few more weeks before the warbler chicks fledge and prepare to fly south for winter. Already, Reitsma is encouraged about the new pieces they’ve added to the puzzle, and he’s excited about going to Ecuador this winter to study the Canada warblers in their nonbreeding grounds.

He’s feeling good on a different level as well. After 20 years of research, he’s still out in the field doing what he loves, an uncommon accomplishment for a scientist at that advanced stage of his career. Further, he’s doing work on land that he, personally, played a role in conserving. Shortly after Reitsma and his wife, Denise, moved to Canaan in 1986, he became involved with the Canaan Conservation Commission and has been a member ever since. He served as commission chair for 10 years, and during this time, the commission established two town forests and a conservation fund, which is used to offset the costs of conserving land in Canaan. Reitsma was also among the founding members of the Mascoma Watershed Conservation Council and helped raise funds so that the group could purchase and conserve the Bear Pond Natural Area.

The emerging results of his work are justifying the conservation. “That feels good,” he says. “That feels really good.”

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