Autumn heralds its arrival with all manner of colorful cues: Tree leaves explode into brilliance; gray squirrels feverishly hoard food supplies; yellow school buses come out of hibernation, and most remarkably, blackbird flocks practice their aerial gymnastic routines.
Teachers, daycare workers, and other sorts of cat-herders are no doubt impressed that Canada geese manage to organize V-shaped follow-the-leader flight formations without any noticeable squabbling. With all due respect to migratory geese (and to those tasked with maintaining order amid groups of youngsters), watching a flock of tens of thousands of blackbirds turn, wheel and dive in unison is far more captivating. Although grackles, cowbirds and the invasive starlings are lumped into the category of blackbird, it’s our native red-winged blackbird (Agelaius phoeniceus) that I most often see in the St. Lawrence Valley.
Considering that red-winged blackbirds are the most numerous bird species in North America, it seems odd that their migration often escapes our notice. After all, their flocks are much larger, in terms of numbers, than those of geese. In fact, Richard A. Dolbeer of the USDA-APHIS Wildlife Services in Denver says that a single flock may contain over a million blackbirds.
Canada geese migration is hard to miss. Even if their chevron-shaped flocks don’t catch your eye, their loud honking will let you know what’s up, so to speak. But blackbirds are smaller and migrate primarily at night, plus they don’t have the pipes that geese have, and their voices don’t carry as far. And admittedly they aren’t as numerous in the St. Lawrence Valley as they are in the upper Midwest.
All blackbirds, red-wings included, are omnivores. They feed on insect pests such as corn earworms, as well as on weed seeds, facts which should endear them to us. Unfortunately they sometimes eat grain, which has the opposite effect. Studies indicate they seldom cause significant damage to crops.
Along with robins, they’re one of the first signs of spring. Usually I hear them before I see them; the males’ “oak-a-chee” call is music to my ears in more ways than one. And the red and yellow wing patches, or epaulets, of the males are a welcome splash of color in the sepia-and-snow tones of mid-March.
Red-wings often nest in loose colonies in marshes. I recall canoeing with my young daughter through cattails, peering into red-wing blackbird nests while adults hovered overhead, objecting loudly and sometimes diving a bit too close to our heads. Marshes afford red-wings some protection from predators like foxes and raccoons, and the females, which are a mottled brown, blend in well. Hawks, and owls to a lesser extent, take a toll on blackbirds regardless of where they nest, though.
In the fall, blackbirds flock together before migrating to locations in the southern US. This is when they display their avian acrobatics. Perhaps you’ve driven along great undulating flocks of blackbirds and marveled at the way they’re able to all change course instantly.
One morning this fall a great number of red-wings landed in a large sugar maple in my yard. I watched in awe as they streamed up out of that tree and poured themselves back down into another large maple nearby. They repeated this “avian hourglass” performance several times.
Researchers have long puzzled over synchronized flock movement. In recent years they’ve made some progress thanks to high-speed imaging, algorithms and computer modeling. In fact, movie animators have cashed in biologists’ algorithms to better depict movements of fish and herd animals.
Apparently, each bird keeps track of its six – no more, no fewer – closest neighbors, and coordinates its movements with them. No matter how many times they turn or dive, they maintain about the same distance between themselves and the six closest birds.
But precisely how do birds maintain distances within a flock, or know when to change course? In the words of Claudio Carere, an Italian ornithologist deeply involved in studying starling flock behavior in Rome, “The exact way it works, no one knows.”
I like an honest researcher.
Photo of Male Red-Winged Blackbird courtesy Alan D. Wilson.