The Mountain Times

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In This State: The mysteries of bobolinks

A tiny yellow and brown bobolink sat frozen in scientist Noah Perlut's hand, the bird's head caught between his middle and second fingers.

Her bright black eye darted from side to side as Perlut's assistant, Jenna Cava, used Kevlar thread to tie a little package to the bird's back.

"A little tighter, but not too tight," Perlut said. Cava dabbed glue on the knots to hold the "backpack" secure.

The backpack, about the size of a pencil eraser, carries a light sensor called a geolocator. When the bird flies south this fall, the tiny device will record the intensity and timing of light levels each day.

If Perlut can recapture the bird next spring, the data on the changing length of daylight will allow him to calculate each day's latitude and longitude and thus create a map of her 12,000-mile round-trip migration.

Geolocation is just one of several ways research in Shelburne and Charlotte hay fields has begun to reveal, and to unravel, the mysteries of bobolinks, those yellow-capped monarchs of spring-time meadows.

Bobolinks are in steep decline in Vermont, where development and changing farm practices have made it more difficult for the grassland songbird to nest and safely fledge its young.

Bobolinks would be missed. Their bubbling song brings meadows alive and their aerial acrobatics during mating are well known to birders and farmers.

"They are so showy, with that yellow head and their bobbly bubbly song," said Sarah Cayea of Essex, who came to know the bird on horseback rides as a child and who now is one of Perlut's summer assistants. "They are an essential aspect of Vermont for me."
Almost no one knows bobolinks as well as Perlut, who began his research here as a University of Vermont graduate student 12 years ago.

Although he is now an assistant professor at the University of New England in Biddeford, Maine, he returns each spring to catch and band bobolinks and to ask new questions about the species.

Twelve years of research on a single species in a single area is extremely unusual, UVM biologist Allan Strong said. It allows Perlut to ask, and perhaps answer, tough questions about bobolink behavior and genetics, because he has captured several generations of birds.

"The first word to describe Noah is tenacious," Strong said. "He knows what every single bird in that field is doing. He knows some of these current residents' parents, grandparents and even great-grandparents… That is rare, extremely rare."

A bobolink in the hand is a wonder; one is immediately struck by its beating heart that's scarcely protected by translucent skin and feathery down.

Each bird weighs about an ounce, yet these durable little creatures are able to fly 6,000 miles to Argentina in the fall, then return unerringly to this field or one nearby the following spring.

This morning, gauze-like nets strung in the field have yielded a bumper crop of birds. Student assistants untangle the birds gently from the webbing and bring them to Perlut in soft cloth bags.

Perlut sits cross-legged in the grass, wearing a snug watch cap, fleece jacket and waterproof pants as protection against an unusually cool breeze and morning dew. A fishing tackle box holds thread, bands, glue and other equipment.

He has been capturing birds in this field for so long that each bobolink he plucks from a bag already wears colored bands attached in previous years.

4--Bobolinks --instate 14Pix2

One of the first birds to wear a geolocator was born in this field. When ornithologist Roz Renfrew analyzed the data the bird carried back from his 2009-2010 migration, she discovered that during his return he had flown from Venezuela to the Bahamas, a 1,100-mile trip, in a single day.

This research is possible because of an earlier important finding of the Shelburne research: Apparently alone among mainland songbirds, bobolinks return to their natal fields, or ones nearby, to breed. That means Perlut is able to study the entire life history of a bobolink.

Perlut calls the returned fledglings "birthday birds," because he recaptures them roughly on their birthday, and "when we find one, it's like unwrapping a present."

This bobolink pattern allows him to consider the characteristics and behaviors that are linked to a fledgling's survival, its ability to make the round-trip migration and to mate and raise young of its own.

It is that reproduction down several generations that defines a successful genetic line.

"When you have kids, you haven't proven fitness. You prove your fitness when you have grandkids: you have produced children that can produce children," Perlut says.

This year he hopes to attach geolocators to at least one parent and one offspring from each nest his team is able to locate.

"Does the nestling migrate at the same time and to the same place as the parent?" he asks. The assumption has been that, for small birds that migrate by the millions,  "each individual is on his own," not traveling in a family group.
Is that truly the case?

Much of Perlut's research is aimed at increasing scientists' depth of knowledge about bobolinks, but work he has done with UVM's Strong has had broader practical results.

Early on, they discovered that when farmers take repeated hay crops from a field, which they often do, bobolinks in that field fledge zero young.

But if the first crop hay is cut early, say, before June 1, and then the field is left untouched for 65 days, the birds will have enough time to build a second nest and raise their young.

Trouble is, farmers, particularly dairy farmers, pay a price for that 65-day delay because the second cutting of hay will have less nutritional value.

Perlut's and Strong's findings led to an experimental U.S. Agriculture Department conservation program that paid farmers $135 an acre to delay that second cut. The program was particularly attractive to farmers who raise hay for horses, which can thrive on lower-quality hay.

About 1,300 Vermont acres were enrolled in the program, until the government dropped the incentive to $86 an acre and now has found no takers. This year Strong and a Connecticut professor are studying whether private fundraising can generate enough money to protect some bobolink nesting grounds.

Perlut's head is always full of dozens of bobolink questions he would like to answer, from whether bobolinks choose the same mates year after year (and whether fidelity affects reproductive success) to whether the shrinking of the yellow head patch on aging male birds affects their success with females.

"In an ideal world, I'd keep on this project forever," said Perlut during one of his morning visits to the field.
Though the bobolinks are research subjects, Perlut, the scientist, is not above waxing poetic. "They are so interesting and mysterious, from this spectacular migration to the joy of their song and dance in the air," he says of the birds.

 "I can't imagine a summer not full of bobolinks."

Candace Page is a freelance journalist in Burlington.

Photo by Candace Page

Photo courtesy of Professor Allan Strong, University of Vermont