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TRYING FOR PURPLE MARTINS

During our 23-plus years at Hilton Pond Center, we've found nests for 24 bird species; for another 39 we've captured and banded females with active or recent incubation patches that imply breeding on-site or nearby. Several nesting species have taken advantage of artificial cavities--i.e., nest boxes we've erected on trees, poles, and fence posts. Of these, Wood Duck hens annually lay eggs and fledge young from large boxes along the edge of Hilton Pond, while Carolina Chickadees, Tufted Titmice, Brown-headed Nuthatches, House Wrens, Carolina Wrens, and Eastern Bluebirds have used boxes actually intended for the latter. With the loss of natural habitats and old trees, cavity nesters everywhere have it tough these days, so we do what we can to erect as many nest boxes as possible. One cavity-nesting bird we've always coveted but never accommodated is the Purple Martin, so in 2005 we decided to go all-out in trying to attract this aerobatic insect-eater. At long last and with some effort, we finally erected a Purple Martin high-rise on the pier at Hilton Pond.

All text & photos © Hilton Pond Center

The Purple Martin is one of those birds that has almost mythic status among backyard bird enthusiasts. Each year, hundreds of thousands--maybe millions--of North American bird lovers put little white duplexes and hollowed-out gourds on the tops of tall poles in the hope of enticing martins to take up residence. Many of these folks fail at their goal for any number of reasons: The nesting structures are erected too late in the season, they're placed in inappropriate habitats, gourds or apartments are poorly maintained, indiscriminate use of pesticides kills or contaminates local insect populations, or--heaven forbid--a flock of invasive European Starlings usurps the martin houses.

Purple Martins, Progne subis, are the largest North American members of the Swallow Family (Hirundinidae), reaching 7" from tip of bill to end of tail. The eastern subspecies breeds in Cuba and across the eastern U.S. to the Rocky Mountains and throughout southern Canada as far west as British Columbia (see map at page bottom). A western counterpart is restricted primarily to the Pacific Coast from Vancouver to Baja California and into western Mexico. All these birds depart in early autumn and overwinter in South America. Interestingly, the western subspecies tends to nest in natural cavities such as hollow trees and old woodpecker holes, but here in the East our Purple Martins nest almost exclusively in artificial structures such as apartment houses we humans build and erect.

This penchant for "unnatural" cavities was well known to Native Americans, who grew gourds and hung them around their villages and agricultural fields. Nesting near humans could have become "fixed behavior" in eastern martins because nests near Indian settlements were likely more successful when potential predators didn't wander into villages to take martin eggs or chicks.

Purple Martins returned the favor for indigenous people, reportedly chasing crows away from plots of corn and eating insects that might devour the crop. Indeed, Purple Martins are prodigious eaters of flying arthropods--a behavior noted by early European immigrants who expanded the Indian tradition by putting up wooden houses and both clay and natural gourds. Even John James Audubon chose to depict long-winged Purple Martins nesting in an old gourd hung in a tree (above left).

All these martins undoubtedly impacted on Colonial insect populations, primarily ants, bees, dragonflies, moths, butterflies, flies, beetles, and stink bugs. For decades Purple Martin "authorities" spread the word that an individual martin would eat up to 2,000 mosquitoes per day (see sign above right), but fecal analysis shows this is far from true; martins may eat a few, but they almost always go for bigger prey and leave the 'skeeters for bats and dragonflies to consume. In other words, despite the urban myth Purple Martins do NOT consume significant numbers of mosquitoes and shouldn't be looked to as a biological control for West Nile Virus.

There's no doubt that Purple Martins are highly social creatures, nesting in dense colonies and roosting by the dozens on power lines. Adult males (below left)--whose iridescent hues give the species its name--typically migrate ahead of the main flock and scout areas for potential nesting sites. Many colonies use the same sites year after year, of course, so it is young (second-year) birds that arrive a month or more after the older martins that find new locations where a hopeful human homeowner has hung gourds or erected houses. Since there have been no nesting martins here at Hilton Pond Center at least since 1982--if ever--it's those young scouts whose attention we hope to capture for the 2005 breeding season.

Purple Martins like open areas, so the Center is not an ideal location. When we moved here 23 years ago, the property was old fields and that has tuned into young woodland. In 1982 there was even a ramshackle martin house on a pole in a grassy plot across the pond. We have no way of knowing whether this structure had ever been used, but if is was then perhaps there's still some "genetic memory" in some Purple Martin scouts that might steer them toward new gourds we put up this week.

Those we erected were "Big Bo Gourds," white plastic containers graciously donated to Hilton Pond Center two years ago by S&K Manufacturing in O'Fallon MO but that we didn't ever find time to put up. The company also provided a high-quality extendable aluminum pole, but the only place that was open enough to accommodate the whole contraption was Hilton Pond itself. In talking with several Purple Martin experts, we learned that putting a martin house on a dock or pond bank was actually a pretty good idea. The water attracts insects that martins eat, and the big, white gourds stand out against the dark water--making them easy for scouts to see.

All text & photos © Hilton Pond Center

So that's our strategy. We hammered a 2" iron pipe into the pond bottom and attached it to one of the pilings that holds up the Hilton Pond pier. Then we clamped the bottom section of S&K's triangular aluminum pole to the pipe, all of which provided a very stable support. After affixing 12 gourds to a special pole-topping rack and sliding a predator guard into place, we extended the other three sections of the pole vertically. Now the gourds stand 15 feet above the pier--ready for those martin scouts to scope out. The Big Bo Gourds are well-made of high-density polyethylene, but we wish ours were of S&K's new design with a screw-off cap on the back--an innovation that would make it much easier to access a nest to band any chicks that might be produced.

The first Purple Martins of 2005 were reported from the Carolinas during early February--right on time according to typical arrival dates on the spring migration map (below left)--but these were adult males unlikely to set up shop at Hilton Pond unless their traditional colony site nearby is unacceptable for some reason. Instead of catching the eye of these early scouts we will wait for the arrival of second-year birds looking to colonize a newly available location. It's a bit early for them, but we were eager to hang our gourds at the Center this week as we try at last for our first nesting Purple Martins. We'll keep you posted on the outcome.

All text & photos © Hilton Pond Center
Migration map courtesy Purple Martin Conservation Association

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SPECIES BANDED THIS WEEK:
American Goldfinch--33
Chipping Sparrow--1
Carolina Chickadee--2
Dark-eyed Junco--6
Northern Cardinal--2
Purple Finch--1
Mourning Dove--1

* = New species for 2005

WEEKLY BANDING TOTAL
7 species
46 individuals

YEARLY BANDING TOTAL (2005)
16 species
297 individuals

BANDING GRAND TOTAL
(since 28 June 1982)
124 species
45,604 individuals

NOTABLE RECAPTURES THIS WEEK
(with original banding date, sex, and current age)