By Penny Briscoe
The purple martins’ perilous 5,000-mile migration from Brazil to Michigan is now underway. Adults, which arrive as early as late March, head by instinct to last year’s nesting site, if it still exists, or search purposefully for a new one. The yearlings, which arrive between mid-May and mid-June, seek out a colony with space and hope to establish a lifetime summer residence.
These Federally protected, native migratory songbirds are the largest of the swallows at 2 ½ ounces. They nest only in human-provided housing near people to be safer from predators like hawks, owls, and raccoons. Colony-type houses or gourd clusters must be typically at least 40 feet from tall trees and, in Michigan, near water.
Their dependence on humans began with Native Americans who hung gourds in their villages for entertainment and insect control. American settlers continued the tradition by building ornate housing. As John James Audubon wrote in 1831 in one of his published journals about birds: “Almost every country tavern has a martin box on the upper part of its sign-board; and I have observed that the handsomer the box, the better does the inn generally prove to be.”
These insectivores feed only on flying insects, and the first birds each spring risk their lives to get the prime real estate. Insects do not fly when temperatures are below 55 degrees, and three or more days of prolonged cold, wind or snow means starvation. The thousands of humans in the country today who seek to attract these birds often assist by setting out in trays fresh-frozen crickets, mealworms or scrambled eggs to sustain them. But it is unnatural behavior for them to eat like this, unless somewhere in their travels they have been conditioned by a persistent person to do so.
These concerned volunteers, called “landlords,” may also track spring arrival, monitor nests to increase fledging rates, and supply important observations and data to the Purple Martin Conservation Association. In many states, they sponsor well-attended purple-martin festivals for fun and education that provide children with hands-on experiences.
Yet, with these efforts, purple martin numbers are plummeting, especially in the Great Lakes region. “Of the swallow gild (a group of species), hands down, purple martins have an abundance level very much more in decline,” said Caleb Putnam, Michigan Important Bird Areas Coordinator for the National Audubon Society.
Theories about the decline include a shortage of nesting cavities due to loss of human interest, climate change, insect shortages from heavy pesticide use, and the invasive European starling and English sparrow, which out-compete the purple martin for nesting cavities and raise multiple broods annually compared to the purple martin’s one. Controlling these two invasives is legal: The U.S. Migratory Bird Treaty Act does not protect them.
The bubbly songs and happy chortles of purple martins often can be heard high in the sky. They maneuver and dive in aerial acrobatics to capture their prey. “They … are known to be effective pest controllers,” according to the Museum of Zoology at University of Michigan. Amish farmers often host large colonies for this purpose, and, they value them for entertainment and the longstanding tradition of welcoming them on their land.
Purple martins often are banded to study their migration. They also have been linked to the pollination process by consuming related insects and spiders, according to the U.S. Department of Agriculture. Some have been outfitted with geotrackers to study the atmosphere. In the South, purple martins are flying as high as 6,500 feet while consuming invasive fire ants and other insects when they descend. “We calculate that across the entire southern U.S., purple martins eat billions of dispersing fire ant queens—each one a potential new colony—every year,” according to University of Oklahoma research.
“Birds are a very important part of the ecosystem, and removing them upsets the system,” said Kellogg Bird Sanctuary Manager Lisa Duke.