Purple Martins

One mid-July afternoon near our barn, our son Steve watched two purple martins insect-catching high in the sky. Several days before, down in nearby Sinking Valley, Steve had driven up a private road called Purple Martin Lane and found two large purple martin houses set up by a local Amish family.

“There were at least 50 purple martins using them,” he told me.

The martins he identified here were the 173^rd bird species for our mountaintop property, and Steve thought they had come from the Amish farm he had visited because it was only a few miles away as the crow (or martin) flies.

The next time I drove to the valley I looked more carefully for purple martin houses and found two more Amish farms, out in the open, with two active martin houses.  Only one of each had four gourds hanging below, but I learned from Amish friends that they were growing more gourds for those Amish and other interested farm families to use as purple martin housing.

Purple martins live throughout North America, but those in the eastern part of the continent are wholly dependent on housing provided by humans. That’s because Native Americans fashioned homes for them from hanging gourds and pioneering farm families did the same. Both were interested in these large swallows that specialize in flying insects especially the flies that swarmed over their game and other food. This thousand-year human/martin relationship led to a remarkable trust on the part of purple martins toward humans, so much so that researchers believe purple martin housing should be erected within 100 feet of a human dwelling and 40 feet from the nearest tree.

Pennsylvania is close to the northeastern edge of the contiguous range of purple martins even though they nest as far north as southern Canada. Between Pennsylvania’s first and second atlasing periods, the martin population “contracted dramatically” according to John Tautin, writing in the Second Atlas of Breeding Birds in Pennsylvania, with losses most notably in northeastern and southwestern Pennsylvania, and central Pennsylvania’s Mifflin and Juniata counties. However, as I discovered, martins are more common in Pennsylvania where there are Amish farms.

While these cavity nesters have adopted apartment and gourd nesting in the East, their ancestral nest sites were abandoned woodpecker holes in dead snags. Yet, by 1900, the eastern purple martins had converted almost entirely to human-made houses.

Purple martins are the largest swallows in North America. The males are entirely purple but appear black in the field while female purple martins are pale below with a pale collar and forehead. They arrive in northwestern Pennsylvania from their winter homes in Amazonia Brazil near Manaus in late April, according to studies by Dr. Bridget Stutchbury and her students. By putting geolocators on five purple martins, those researchers found that it took the birds on average 23 days at 180 miles a day including a nonstop Gulf of Mexico crossing to reach northwestern Pennsylvania. However, one martin made it in 13 days which meant that it flew 300 miles a day.

Male purple martins arrive first and try to claim as many compartments in a birdhouse as possible and sometimes multiple gourds too. If each porch in a birdhouse is divided by a barrier that prevents a male seeing into the adjacent apartments, a single male defends less territory. This enables more martins to occupy a house.

To attract a female to his nest, a male flies from his nest cavity, sailing in a wide arc, and then returns to his nest site, ending in a steep dive. As he lands, he enters his nest, turns around, pokes his head out and sings. A female, more interested in evaluating the nest cavity instead of the male, visits it repeatedly over several hours. Finally, he treats her as his mate and starts accompanying her (mate-guarding) when she leaves the nest site. After several days they move in together and greet each other whenever they are separated.

Purple martins have a wide variety of calls and songs, but the male uses a series of clicks called the “croak song” and the female a “chortle song” during courtship. Most famous is the very loud “dawn song,” which is used before daylight perhaps to attract other martins to the bird house.

Studies of nest preferences for purple martins indicate that they like the higher compartments in bird houses and the deeper they are, the more fledglings they can produce. Best of all are the gourds that are so deep that the martins can raise seven young in them instead of the more usual four in the birdhouse compartments.

Nest-building in Pennsylvania begins in early to mid-May and is mostly done by the female purple martin, although the male may collect green leaves and sometimes starts nest-building by gathering a few twigs or leaves. But once the female begins, he either accompanies her while she gathers nesting material or sits near the nest cavity and watches.

She builds her nest out of twigs, stems of herbaceous plants, leaves, and mud, but each pair designs their own nest so they vary widely in shape. The depressed nest bowl is filled up with green leaves that often hide the three to seven white eggs the female lays. In Pennsylvania, returning martins reuse the same nest cavities and fledge more young than those that use clean compartments.

The female has a brood patch and is thought to be the incubator during the 15 to 18 days of incubation, but the male often relieves the female for long periods and sits on the eggs.

The altricial young hatch and are brooded by the female until their eyes open in 10 days. Both parents feed the nestlings and when they are 12 days old, they cluster together near the entrance hole to greet their parents. By the time they are 17 to 21 days of age, they have their feathers and are exercising their wings by stretching and flapping. Finally, they fledge when they are 28 to 29 days old. In northwestern Pennsylvania that is mid-July on average.

Their parents continue to feed them for several days, but the young begin catching insects on their own and are fully independent seven to 10 days after they fledge. Then they join other fledglings in roosts.

Back in 1990, my husband Bruce and I visited James Hill, who had founded the membership and research-based Purple Martin Conservation Association in Edinboro, Pennsylvania. Already, Hill had set up a variety of nesting apartments and assemblages of gourds to figure out the kinds of nests purple martins preferred. He also published an excellent quarterly periodical called Purple Martin Update, which is still being published.

Today the PMCA is housed at the Tom Ridge Environmental Center under the leadership of Joe Siegrist. In late summer he takes people on pontoon boat tours near sunset to view the huge martin roost of 20,000 at Presque isle Bay, which draws in birds from at least a 250-mile radius. Under their program called Project Martin Roost they’ve discovered at least 350 premigratory roosts in eastern North America and Canada. Most of these roosts are so large they show up on weather radar.

Usually the roosts are over large bodies of water with cover from reed beds and long brushy islands, but in urban and suburban settings they roost in trees or on manmade structures such as bridges and pipes. The farther south these roosts are, the longer the martins remain. Some are used from eight to 12 weeks.

But Stutchbury’s geolocator studies show that once the Pennsylvania birds set out for the south, they fly almost nonstop until they reach Central America as soon as five days later. Then they rest before continuing on to Brazil more slowly than when they head north in the spring.

Other research projects the PMCA engages in with citizen scientists are a Scout-
Arrival Study that tracks the northward migration of the first martins to be sighted at individual colonies and Project Martin Watch, a continent-wide effort to study the nesting dates, number of eggs laid and hatched and how many nestlings survived. They’ve also been banding martins since 1987.

Wet weather is the largest threat to purple martins. If there is a long, cold, rainy spell in June and July, most of the year’s progeny will perish of cold, drown in their nests, or die of starvation since martins don’t fly in wet weather. European starlings and house sparrows may take over martin nests, so martins depend on their human landlords to remove the non-native invaders.

Owls and snakes are also a threat and deeper cavities make nests harder for owls and other avian predators to reach into. Snake guards installed on birdhouse poles can keep them away from the birdhouses.

With enough folks willing to be purple martin landlords, the eastern population of this beautiful bird should grow and thrive.