The first call came on July 21. A lakefront resident along Sheridan Road in north Evanston reported “a very large raptor with a very white breast and a band on one leg” had attacked her Purple Martin house and made off with a nestling. In addition, the house doors were askew.

The e-mail arrived the next day. “We had quite an event today.  Upon hearing lots of noise from our Purple Martins, we saw a large hawk on top of our Martin house.  The Martins were dive bombing it, to no affect.  Eventually I squirted it with water and it flew off. Unfortunately it flew to our neighbor’s Martin house, where it managed
to pull a young Martin out and eat it.  Twice, before I could chase it
away.” This message was accompanied by images (see picture) that left no doubt that the culprit was a red-tailed hawk.

July 23: Hawk back this morning.  Took a chick from our house.  Shows remarkable dexterity.  Wonder how it learned to do this.  Maybe it’s a common practice, though we have never seen this in the 20+ years we’ve been Martin landlords.”

The identity of the individual raider cannot be precisely determined unless someone can read the band number. Since 2005, all banded red-tailed hawks in our area have been released from Willowbrook Wildlife Center in Glen Ellyn, which rehabilitates injured birds. The birds are fed on mice during their stay, and it is not surprising that they would be fearless around humans.

Purple Martins (Progne subis) are native to the western hemisphere and are our largest swallows. Purple Martins are not really purple. Adult males are a glossy midnight blue-black, while the females and juveniles have whitish-grey bellies. Like most swallows, they have forked tails and long, pointed wings. Dynamic flyers, they can turn on a dime and snatch an insect from the air.

They spend the winter months in Brazil and arrive in our area from early April through mid-June. First arrivals are older males. They are faithful to their boxes and will return annually to locations of previously successful nesting spots.

Humans have long been charmed by Purple Martins. Originally, martins sought out old woodpecker holes and other natural cavities. Martins were prized by Native Americans for their beauty and “crazy” aerial displays, as a current Ojibwe website puts it. More practical natives possibly attracted them to scare animals away from food, drying hides and meat. Tribe members made holes in large gourds and hung them in groups from poles. The martins came and stayed. Now, east of the Rockies, Purple Martins depend almost exclusively on manmade housing, though the style has changed to white, multi-roomed, elaborate faux-colonial, perched on tall poles about 15-20 feet above ground. (In the west, Purple Martins still nest in the wild, in crevices, under bridges and in holes in saguaro cacti.) Communal nesting is more common in houses than in the wild.

The care and feeding of Purple Martins is a big responsibility that can mimic a full-time seasonal job. Checking boxes routinely and often, eliminating mites and competing species, protecting against prey, all are required to support martin colony survival rates.

Purple Martins are insectivores. Long rumored to dine primarily on mosquitoes, seven years of study by the Purple Martin Conservation Association (PCMA), a non-profit research and conservation organization, reported a diet including “dragonflies, damselflies, flies, midges, mayflies, stinkbugs, leafhoppers, Japanese beetles, June bugs, butterflies, moths, grasshoppers, cicadas, bees, wasps, flying ants, and ballooning spiders.” Not a single mosquito was found. During drought, extreme heat and storms, when insects are scarce, they will eat mealworms and even scrambled eggs. (Search on line for “Martins Eat from Bed and Breakfast.”)

Females select a nest box and mate combination, though it is anyone’s guess on what basis. Both sexes are involved from nest-building through raising young. Purple Martins are monogamous throughout one season, but both sexes are promiscuous.

Good architectural house design is extremely important. The larger the compartments the better for the martins, but also the better for competitive non-native species such as cavity-nesting European starlings and house sparrows. The placement of the entrance hole, its size, porch style, size and division of interior rooms, protection from the elements and predators, consistent house orientation throughout the season, all make a difference to nesting success.

Since owls are by far the Purple Martin’s greatest predator, with hawks, crows, raccoons and opossums following close behind, owl guards to prohibit predators are essential. PMCA offers many helpful hints and accessories to outfit the houses and poles with safeguards.

The placement of the house is crucial. Researchers recommend a minimum of 40 feet from the nearest tree. The Purple Martin needs space to perform. Donald and Lillian Stokes, in “Bird Behavior,” report that, when attempting to attract a mate, the “male flies away from the nest hole in a large circle and on the return flight starts a steep dive toward the nest hole with wings flapping below the body line. Upon entering the hole, he immediately turns around and, with head protruding out of the hole, sings.” These lovely, graceful birds are very musical, with at least ten different vocalizations identified by the Stokeses.

Currently, over a million North Americans have erected Purple Martin houses. Despite this, the population of Purple Martins is declining for reasons unknown.

Purple Martins collect in large groups before they migrate. In bygone days, thousands of Purple Martins gathered along the lake in August, but those huge roosts are a thing of the past. Most of this year’s Purple Martins left Montrose Harbor as of Aug. 24, on their way to the Amazon.

Libby Hill

Libby Hill is the author of "The Chicago River: a Natural and Unnatural History. She has been writing about birds and trees and Evanston's natural history for the Roundtable since 2004.