For the Birds Radio Program: Purple Martin
Purple Martin houses I just moved into a new apartment in Ithaca, New York. My house and my husband are, of course, in Duluth, Minnesota, but since my job is in Ithaca, I do need someplace to live when I’m there. My first apartment was in the country, 6 miles from work. I woke to bird song every morning, but since this was a country road with a 45-mile-per-hour speed limit, every recording I made from my balcony was tainted with roaring car engines. I also wasted energy commuting, and the duplex was not designed to be energy efficient. My new apartment is less than a mile and a half from work, a pleasant walking distance, and although it’s in a huge complex, I can hear as many birds here as I could from the old place. What I’ve lost in privacy I’ve gained in a sense of community. Each building here has 18 units, laid out rather like the holes in a Purple Martin apartment building, and in the week I’ve been here, I’ve already had some insights into the benefits of life as a Purple Martin. Martins are very sociable, but each pair defends its own nesting compartments. They respect one another’s boundaries, so virtually never come to blows, and find that community living has great advantages over isolation.
Coincidentally, this year we’ve set out two Purple Martin houses in Sapsucker Woods, at the Cornell Lab of Ornithology. We don’t know yet if we’re going to attract any—this declining species has lost numbers just about everywhere, and appropriate nesting sites are no longer the main limiting factor. Purple Martins seem to have been hit by a whole lot of bad things all at once. Pesticides probably don’t have a significant direct effect, but probably have serious secondary effects, since Purple Martins eat flying insects and nothing but flying insects. They don’t consume as many mosquitoes as their PR would suggest, so the form of BT that kills fly and mosquito larvae probably doesn’t impact them, but other forms of BT, and more general insecticides, eliminate much of their food resources.
Water quality is also crucial. Purple Martins migrate during a peak emergence of mayflies from clean, well-oxygenated lakes, rivers, and streams. When fertilizers and other nutrients run off into these waterways, they end up choking up the water with an overgrowth of plants. The decomposition of dead leaves and entire plants depletes the water’s dissolved oxygen, which wipes out the mayfly population. Warmer temperatures exacerbate this process, which is called eutrophication.
Purple Martins are still relatively common, and still need safe housing. Unfortunately, some people who put out martin houses don’t follow through giving martins the help they need. House Sparrows and starlings not only compete for apartments—they also actively kill baby martins. So martin houses should always be constructed on a telescoping pole that can be brought down for maintenance and for evicting nest materials before sparrows or starlings can get very far along.
Houses should also be of the right design. There should be dividers between entrances so that when the first baby starts wandering out of its family’s hole, it can’t wander into another family’s compartment—if it does, the neighbor adults are likely to feed it rather than their own babies, and meanwhile its real parents won’t know where the heck it’s gone. Ideal housing for martins are artificial gourds, available from the Purple Martin Conservation Association. Their website, at www.purplemartin.org, provides a wealth of information and resources to help us restore this magnificent and most welcome bug eater to its former numbers, so they can long continue to teach us how to be good neighbors.