Scientists study effect of climate on purple martins

Chuck Fullmer and the purple martin houses he has at his business near Harbeson.

Chuck Fullmer and the purple martin houses he has at his business near Harbeson.

REHOBOTH BEACH — In a suburban backyard near Rehoboth Beach, Carlton Updyke’s colony of purple martins is thriving.

The same is true of Chuck Fullmer’s colony – along a commercial strip off Del. 5 southeast of Georgetown.

But for martin landlords further north in Pennsylvania, the picture is less robust and some researchers believe that as we experience earlier springs – a possible impact from a changing climate – there may be a mismatch between the time when insects hatch in huge numbers and the arrival of insect-eating birds like purple martins.

“There’s a disconnect and it’s getting bigger,” said Nanette Mickle, a purple martin researcher who maintains a research martin colony in northern Virginia and has been working with a team of scientists to figure out what is happening with martin populations to the north. “Our northern birds cannot keep up with climate change.”

Martins are flying insect eaters. They are completely dependent on human landlords for nesting sites east of the Rocky Mountains so folks like Updyke (who also maintains nest sites at Rehoboth Beach Yacht and Country Club and Delaware Seashore State Park) and Fullmer, along with dozens and dozens of other folks in Delaware, play a part in keeping the population stable and growing here.

The state’s most recent Breeding Bird Survey indicates an increase both in population and distribution, probably because of state residents installing nesting houses to attract colonies, said Anthony Gonzon, with the state Breeding Bird Survey.

It hasn’t always been this way, according to the Purple Martin Conservation Association. Back some 12,000 years ago, before human settlement, martins probably nested in abandoned woodpecker nesting chambers or other tree cavities. Then, Native Americans started putting up nesting gourds to attract the birds.

The martins likely thrived being closer to people, with the added protection from predators and a bounty of nesting spots.

In return, the martins arrive on a regular schedule each spring, set up nesting in houses or gourds and take a bite out of flying insects. Contrary to popular belief, they aren’t big mosquito eaters. But they do eat lots of other flying bugs.

Because of their diet, weather can be a big factor. If it rains for several days in a row and insects aren’t flying, martins can starve. If it gets too hot, the baby birds can perish.

Purple martins on one of Chuck Fullmer's colonies. / GARY EMEIGH/ THE NEWS JOURNAL

Purple martins on one of Chuck Fullmer’s colonies. / GARY EMEIGH/ THE NEWS JOURNAL

Last summer, Fullmer hand-fed one of his baby birds to keep it alive through a summer heat wave. That spring and summer were among the warmest and earliest on record for the Mid-Atlantic region.

A study by the U.S. Geological Survey looked at last spring and the impact it had on everything from flowering plants to animal life cycles. Spring came as much as 20 to 30 days early in the East and Midwest last year, according to the USGS report.

But purple martins don’t base their migration on temperature or weather patterns. Instead, Mickle said, they migrate based on daylight and day length.

Mickle is part of a research team that outfitted martins with geolocating “backpacks,” small devices that record daylight and length over the course of the year.

Last year, the migration of the birds was out-of-sync with the bloom of plants and insects, she said, especially in areas to the north.

In a newly published study, the research team that Mickle is a part of found no evidence that purple martins adjust their migration to adjust for warmer temperatures in their breeding areas.

The team is now looking for genetic variations in the birds to see if migrants that go to more southern breeding areas may be more adaptable to changing climate and weather conditions than their northern-migrating relatives, Mickle said.

The northern population decline isn’t new, she said. Initially, researchers thought the problem might be some environmentalchange on the wintering grounds. Martins migrate in the late summer and fall to Brazil and then return to the Atlantic Coast in the winter and spring.

“They basically came up with nothing,” she said.

Meanwhile, populations are stable in places like Delaware but declining in Pennsylvania. with dramatic declines in parts of Canada, she said.

With the geolocators, the team has learned lots of new things about the birds. One of Mickle’s birds, for instance, left northern Virginia and was in the southern tip of Florida – 900 miles away – in one day.

“It traveled at night” something we didn’t know these birds did before the geolocating work began.

Fullmer has found the ideal location for a martin colony at his business, Pontoon Express, off Del. 5. The birds seem to like open areas.

He said that it can take a couple of years to establish a colony but once you get 10 to 12 pairs “you’ve got a solid base . . . getting to that point is tricky.”

By mid-August, the birds start to converge along telephone lines as they stage for their southern migration and Updyke takes down his houses in preparation for hurricane season.

His advice to people who want to try being martin landlords is to be patient but he has one other recommendation.

“You must be willing to control house sparrows and starlings,” he said. “Otherwise there’s no need in even trying.”

Purple martins
SIZE: Smaller than a robin, larger than a tree swallow.

APPEARANCE: Males are iridescent, dark purple; females are more drab with gray flecks on head and chest with a white lower belly.

HABITAT: Nesting in colonies, they favor open habitats near water.

• European starlings and house sparrows are common threats to purple martins. They take over nest sites.

• Purple martins converge and roost in late summer – after chicks have left the nest – this roosting behavior occurs in advance of southward migration. A major roosting spot is the old Manns Harbor Bridge just west of Manteo, N.C. in the Outer Banks. In Delaware, birds begin to flock and roost at utility lines along Del. 1 at Delaware Seashore State Park.

• The spring early birds are often referred to as “scouts.” People used to think they returned to make sure an area was safe for nesting. But in reality, they are older martins returning to the place where they have nested before.

• Martins get all their food in flight. To drink, they skim the surface of ponds, pools and other water sources.

• The story goes that martin houses were so common that artist and ornithologist John James Audubon figured out where he would stay the night on his travels based on the quality of the martin house in the yard.

• Purple martins spend the winter in open, grassy areas and agricultural fields of South America such as Brazil and Bolivia.

• At night, they flock to cities and towns to roost in trees of village plazas.

To learn more about martins go to The Purple Martin Conservation Association website at purplemartin.org

Source: www.delmarvanow.com

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