Purple Martin Mania

By John Miller | March 2, 2006
From Missouri Conservationist: Mar 2006

Like many purple martin enthusiasts, I was introduced to these beautiful swallows by my grandfather, who anxiously watched in spring for the return of “his” birds.

As some grandfathers do, mine harbored a few myths about purple martins. One that he kept repeating was that martins always return on Good Friday, give or take a few days.

The arrival of purple martins (Progne subis) from wintering grounds in South America is fairly consistent throughout their range. Scouts usually show up in southern Missouri in early March. When they arrive, however, also depends on the weather. Favorable conditions for the return of the martins and the variable date for Good Friday may simply have coincided enough times to convince Grandpa. That’s usually how myths are born.

I’ve heard many myths about purple martins. Probably the most widely believed myth is that purple martins are voracious consumers of mosquitoes. Scientific studies don’t support this belief. No ornithological research has ever found that mosquitoes comprise more than 3 percent of a martin’s diet.

That makes sense. Like all swallows, purple martins eat airborne insects entirely on the wing, but martins tend to feed high in the sky while mosquitoes remain close to the ground. Martins also feed during daylight, while mosquitoes are most active at night.

Purple martins, which are the largest of our swallows, measuring 7 1/2 inches with a wingspan of 13 inches, do eat a variety of other flying pests such as Japanese beetles and spotted cucumber beetles. They also consume several water-borne insect species, including mayflies, damselflies and large dragonflies. This may explain why martins are less numerous in forested mountain regions, including parts of the Ozarks.

Apartment Dwellers

Purple martins are the only wild bird species largely dependent on human-provided housing. It’s safe to say that if “landlords” took down all martin the houses and gourd racks, the species would suffer.

American Indians manipulated purple martins in the East to abandon tree holes for hollowed-out gourds. Early colonists adopted the custom and added houses to the mix.

Colonies of purple martins exist in most communities and rural yards in Missouri, but they tend to be more numerous in the southern half of the state.

The greater population in southern Missouri is probably due to more martin housing on boat docks and marinas around Missouri’s reservoirs. Martins love a house near water, although they will readily colonize open sites in yards. Southern Missouri also offers many hospitable landlords along rural roads and in small communities.

Super Colony

Camden County is home to what may be Missouri’s largest colony—131 active pairs last season. The birds nest in a combination of aluminum houses, manufactured PVC gourds and an elevated rack of nest compartments made from reconditioned mailboxes.

This “super colony,” maintained by Cheri Warner, is about 12 miles north of Richland. Students from nearby Crocker Elementary School visit the site often on summer field trips.

Standing in front of a noisy colony, you might conclude that there are a lot of purple martins. But, you may be looking at the only colony of birds for miles.

That’s the case in St. Louis City, where the population is primarily limited to a small colony at the Missouri Botanical Garden, a second one at a nearby restaurant parking lot, and to seven to eight pairs recently attracted to new housing in Forest Park. Together, all of those colonies probably contain fewer than 30 pairs of martins.

In the northern half of their range—generally the states north of Missouri—and in pockets of the southeast United States, purple martin numbers have been declining since about 1960. Pressure from European starlings and English house sparrows likely is contributing to the decline. Both species successfully compete with purple martins for nesting sites.

Many experts believe we have only about 10 percent of the number of purple martins that was present in the 1800s. There’s little old survey data to compare, but in notes dated February 1821, John James Audubon wrote in New Orleans of “prodigious flocks moving over the city...I walked under one of them with ease for upwards of two miles.”

Simply Enchanting

Why do so many people love purple martins? Even passionate landlords have a hard time answering.

Purple martins are enchanting. Watching these birds soar, bank and dive is mesmerizing. They chirp loudly and seem to delight in one another’s company.

Migration for purple martins is a drawn-out affair. Last season, one experienced landlord in Webb City reported that a male martin arrived on Feb. 24, well ahead of my grandfather’s schedule. The bird was likely a senior traveler; older birds tend to arrive earlier.

Although many martins arrive in Missouri in March, the bulk of many colonies—mostly 2-year-old birds—lag behind until early April.

One-year-old birds, called sub adults, arrive in late April and well into May. “Subbie” males lack the steel-blue to purple color of 2-year-old males. They resemble females but have patches of dark about the nape of the neck.

Sub adults are more easily attracted to new sites. A sub male may hang out for several weeks at a new site trying to lure in females, which are more finicky house hunters.

Pairs construct a flat nest of straw and spongy plant stems, sometimes adding a mud dam at the entrance. They line the nest bowl with green leaves. They refresh those leaves often to cover the eggs when the female is out feeding.

Broods of older birds fledge around late June, while the broods of sub adults fledge in late July.

Forums for ‘em

Purple martins are benefiting from the Internet. Many devoted landlords now turn to online forums for helpful information. One of the most popular is at purplemartin.org. It’s the site of the Purple Martin Conservation Association (PMCA), a nonprofit advocacy group devoted entirely to purple martins.

Leverett W. Doehring of Villa Ridge in Franklin County, southwest of St. Louis, said information from PMCA forum members helped him grow his colony. Last year, he had 86 pairs with just two vacant compartments.

“A lot of people think you can just put up a house and get martins,” Doehring said. “And, you might get a few, but for a colony to grow, you really need to apply some very specific techniques.”

Much has changed in the last decade in “martin management.” Houses now have deeper compartments to stimulate larger clutches and help protect nestlings from predators, especially owls. Many of them also have specially designed entrances that restrict starlings.

Serious landlords tend to become amateur wildlife biologists, keeping detailed records of purple martin behavior and nesting success. Their diligence will likely result in even more refined techniques for caring for purple martins in the future.

Doehring sat on his deck one evening reviewing notes on egg clutch size, projecting fledging dates, and pondering adding a few more housing units.

“It would be nice to reach 100 pairs,” he said. “I just can’t imagine sitting out here without them.”

Location! Location! Location!

The biggest error you can make when setting out a purple martin house is to put it too close to trees. Open sites, or at least sites with open flyways, attract more martins.

Curiously, martins also seem to prefer nesting in the vicinity of human activity.

Recent findings suggest that the 12-compartment aluminum house with 6-inch by 6-inch rooms that has been widely used since the 1960s is due for a makeover. Experts suggest deepening compartment size to 6 inches by 12 inches. Adding starling-restricting doors is also necessary, because both starlings and martins prefer the deeper compartments.

Many landlords also are putting up natural gourds or those made from PVC. Gourds give martins room and help protect their nests from rain and predators.

Successful landlords invariably suggest aggressive control of starlings and house sparrows. These nonnative species are not protected and can be removed by trapping or shooting.

This Issue's Staff

Editor in Chief - Ara Clark
Managing Editor - Nichole LeClair
Art Director - Cliff White
Artist - Dave Besenger
Artist - Mark Raithel
Photographer - Jim Rathert
Writer/editor - Tom Cwynar
Staff Writer - Jim Low
Designer - Susan Fine
Circulation - Laura Scheuler