For the Birds – Purple Martin

Maine provides breeding ground for six species of swallows. Tree Swallows, the first to arrive in the spring, are the most abundant. Barn Swallows are nearly as common. As colonial nesters, Cliff Swallows and Bank Swallows may be locally abundant. Rough-winged Swallows even less common in the state. But the least abundant is the Purple Martin.

Purple Martins are the largest swallows in North America and among the largest in the world. They are an extremely popular bird, recognized by many non-birders. Males are completely covered with a glossy blue black plumage and are the only swallows in North America with a dark belly. Females with brown upperparts and lighter underparts are similar to other female swallows but can be distinguished by their large size and the prominent brown or gray collar around the nape. A martin’s chattering vocalization adds to their charm.

Although Purple Martins are scattered in parts of western North America (parts of the desert Southwest and coastal areas from British Columbia to central California), they are continuously found throughout most of the eastern states. However, they occur discontinuously in New England. In Maine they occur in a broad swath proceeding northeastward from coastal York County to the Calais region of Washington County. This band continues northeasterly into New Brunswick ending at the northwestern tip of Nova Scotia.

The Maine Department of Inland Fisheries and Wildlife estimates there are probably not more than a couple of hundred pairs in the state. Purple Martins are colonial nesters but Maine colonies are typically smaller than the large colonies one sees in southeastern states.

Although Purple Martins nested in natural cavities before the development of the United States by European immigrants, nearly all eastern birds now nest in human-made apartments. Elaborate martin houses may be used as well as gourds, hollowed out, and hung close together. The provision of houses may have caused martins to become colonial. Martins in the west often nest solitarily in natural cavities. Eastern martins have nested exclusively in human-made cavities since 1900. The geographic difference in nest-site choice is one of the most pronounced of any bird over its range.

Because of their popularity, incorrect information about Purple Martins gets published and reprinted, becoming fact in the eyes of unskeptical readers. Some of these myths pertain to the diet of Purple Martins. Manufacturers of martin houses often encourage the purchase of their products by touting the effectiveness of martins in controlling mosquitoes. Don’t believe it!

Martins tend to feed several hundred feet above the ground and always take flying insects. Their prey are mostly large species like dragonflies, wasps, bees, and Japanese beetles. Martins feed only during the day.

Mosquitoes on the other hand tend to be found in damp grass close to the ground during the day and may only be active at night. No study of martin diets has ever shown mosquitoes to be a significant component of their diet. I suspect that martins may even aid mosquitoes by reducing the populations of dragonflies, which are often effective mosquito predators.

Depending on flying insects for sustenance, Purple Martins are subject to the vagaries of the weather, particularly in New England and the Maritime Provinces. Cold or extended rainy weather during the early part of the summer can reduce the number of flying insects and spell disaster for Purple Martins.

The nesting process is slower than in many other songbirds. Incubation takes place for 15-20 days before hatching. The female does most of the incubation although the male may take a turn while the female leaves the nest to feed. The young do not fledge until 28 or 29 days after hatching.

As one would expect, nesting begins earlier in more southern parts of the range. Females begin laying eggs around the end of March in Texas but not until the first ten days of June in Maine and Nova Scotia.

It’s wonderful to have a martin colony on your property. However, getting a colony established in Maine is a tough proposition. Besides their low population numbers in Maine, martins have specific requirements for their nest boxes. The nest box needs to be higher than trees in the local area and no tree should be within 60 feet of the martin house. The martin house can be placed between 30 and 120 feet from human habitation. Research has shown that martin houses further than 120 feet from human houses are usually avoided. Martins have learned that proximity to a human house lowers the risk of predation. Another challenge is keeping House Sparrows and European Starlings out of the nest cavities.

Lots of useful information can be found at two websites: http://www.purplemartin.org and http://www.purplemartins.com/

[This column was originally published on July 1, 2006]