A Frenzy of Avian Reproduction in Dyke Marsh
Volunteers begin annual breeding bird survey.
“Cheet, cheet, cheet.” “Squeak, squeak, squeak.” “Konkareeeeee.”
A symphony of bird calls resounded Saturday morning at dawn, when Larry Cartwright started the annual breeding bird survey in the Dyke Marsh Wildlife Preserve. By 6:15 a.m., he had identified 12 birds, many by their calls.
“That’s a kingbird,” he announced, to the “cheet, cheet, cheet,” not to be confused with the “chip, chip, chip” of the northern cardinal. The “squeak, squeak, squeak,” which sounded like turning a rusty screw, was a black and white warbler. The “konkareeeeeing” red-wing blackbirds zoomed around the cattails, and grackles fluttered above the spatterdock, as intent joggers and bikers streaked by on the Mount Vernon trail, most oblivious to the avian courtship and mating.
Cartwright records species into one of four categories: confirmed breeder, probable breeder, possible breeder and present. In 2011, of 78 documented species, volunteers found 40 confirmed breeders and 19 probable breeders, including the first-known breeding eastern screech owl. The 2012 totals will be compiled mid-summer.
How does he determine if a bird is breeding? He looks for behavior like birds carrying food or nesting material, mating or nest-building, or young begging parents for food.
“When they beg, they are really persistent,” Cartwright remarked. “It’s really obvious.” The young grackles were going through what he called a “weaning period.” They can feed themselves, but also expect their parents to bring them food. They seem to be in their “teenage phase.”
One highlight this season is a bald eagle’s nest with two young. Keen observers can see their dark brown heads craning out of the nest, probably awaiting delivery of a piscine snack. The young will fledge the first or second week of June.
Cartwright delighted especially in spotting a prothonotary warbler. A striking yellow bird, it nests in cavities in swampy areas. As trees die, leaving snags, woodpeckers drill holes, which become nesting sites for these and other cavity-nesting birds, Cartwright explained. According to Kenn Kaufman in the "Lives of Northern American Birds," the name “prothonotary” comes from a group of Catholic Church scribes who wore bright yellow hoods, as this bird appears to do.
Why does Cartwright drag himself out before sunup to search for breeding birds? “Because I like to,” he answered. “And it provides data to the National Park Service that they otherwise would not have and do not have the money or personnel to collect.” Volunteers will survey four areas of the preserve, by both land and water, until July 4.
Cartwright and others are particularly concerned about two birds, the marsh wren and the least bittern. Dyke Marsh supports the only known nesting population of marsh wrens in the upper Potomac tidal zone, a species once found all along the Potomac River’s marshes. They construct globular nests by weaving dried grass around sedges or cattails.
Surveys show a serious decline in marsh wrens in Dyke Marsh. In the 19th
century, observers saw hundreds of nests along the Potomac. In 1950, 87 singing males were counted and in 1998, 38. In 2011, 10 territorial males
“Since 2000, the number of marsh wrens plummeted,” Cartwright said, probably because of loss of habitat. He believes the least bittern population is stable for now in Dyke Marsh.
Osprey numbers are down this year, from 13 nests a few years ago to seven this year. Ospreys build big, messy nests on trees and other structures along the shoreline. With Dyke Marsh eroding rapidly, shoreline trees are vanishing.
By 9 a.m., the bird calls were competing with the steady din of parkway traffic, airplanes leaving National Airport, chatty walkers and dinging bike bells. A bright red northern cardinal zipped by and disappeared into dense shrubbery.
“That cardinal dove in there like he had a purpose,” Cartwright observed, speculating that the bird was headed to a well-hidden nest.
Cartwright has led the survey for 20 years and was honored for his work by the Friends of Dyke Marsh at their May 16 meeting. By day, Cartwright is an analyst with the U.S. Department of Defense. He also manages the bluebird box survey at Huntley Meadows Park.