Purple martins battle tough odds Cold, competition may hinder species

Six species of swallow breed in Maine, and of these – including the barn, bank, cliff, tree, and northern rough-winged – the purple martin is perhaps the best known. Many people try to lure them to nest near their houses by providing multiple-roomed “condominiums.” These structures, set atop tall poles, are a common site in yards throughout the eastern United States.

Providing housing for purple martins is not a recent a practice. Long before European settlement of the continent and the use of aluminum condominiums, Native Americans began luring the birds to nest around them by hanging hollowed-out gourds nearby.

Someone recently wrote in to ask me about purple martins. He said there used to be several that nested in birdhouses around town; in the past several years, however, they have been absent, and he wanted to know why.

There may be two explanations for this. One is cold weather. Martins feed almost exclusively on flying insects, catching them in mid-air up to heights of 500 feet or so. Insects are less active during spring cold snaps, which makes it harder for the martins to find food. Prolonged low temperatures and bad weather have been known to wipe out local populations of these birds, especially in northern areas. They may also succumb to exposure during inclement weather.

Another reason for this bird’s decline is competition with the European house sparrow and European starling. Both of these birds nest in cavities and will drive out native cavity-nesting species. They have been known to puncture purple martin eggs and kill nestlings and adults by cornering them in the nest and pecking them.

Parasites may play a role in reducing purple martin nesting success. Because of this, it is important that people closely manage their martin “condominiums,” to reduce parasite populations.

The type of housing provided may reduce the number of martins nesting in a given area. Researchers have found that condominiums with no separation between rooms or porches may increase the number of rooms a male martin will defend, excluding others of his kind. Older nestlings may intrude on a nest containing younger nestlings and take the food their parents bring, thus causing them to starve. Rooms and porches that are completely separated from one another will greatly decrease these occurrences, as will hanging gourds.

Researchers have questioned the effect of such close-quarter housing on martin populations. Before people began providing communal nest sites, these birds nested in woodpecker cavities or rock crevices; rarely are these sites joined together or interconnected in any way, as they are in some martin houses.

I found one fallacy about martins through my research into this topic. Although their incredible appetite for mosquitoes has been repeated many times by many publications, according to the Birds of North America, it is apparently not true that they consume more than 2,000 of the bloodsuckers per day. Researchers say this is simply because martins usually forage at heights much higher than mosquitoes reach. In addition, martins feed during the day, while mosquitoes are more active at night.

Glossy ibis spotted

Since the column about the glossy ibis, I have received a couple of e-mails saying that the bird has been seen more often in this area than I had stated in the article. One reader reported seeing one off the Witter Farm Road in Orono in 1996; another was seen last week in Aroostook County, according to Maine Audubon’s rare bird alert. As always, feel free to report your sightings to the Field’s Pond Nature Center. I’d be interested to know if there are purple martins nesting in the area.

Chris Corio’s column on birds is published each Saturday. Corio, a volunteer at Fields Pond Nature Center in Holden, can be reached at fieldspond@juno.com