Texans—especially urban Texans—are intimately familiar with grackles. The chattering, swaggering great-tailed grackle is a common sight in urban areas, with numbers that have boomed to 4.8 million in Texas, the largest state population for the species. Great-tailed grackles are everywhere: roosting on power lines, stalking parking lots, and loitering around outdoor restaurants in hopes of snatching a tasty morsel.
But there is another species of grackle native to the state: the common grackle, found throughout Central and East Texas. It’s smaller and more brightly colored, with iridescent blue-green feathers mixed with striking bronze backs. Like the great-tailed grackle, it’s chatty and social, even if its voice sounds like a rusty hinge. Like its larger cousin, it’s quite numerous, with a current global breeding population numbering around 69 million.
Hidden in that nice large number, however, are signs of trouble. A few years ago, ornithologists “started noticing that the species was showing pretty big declines,” says Michael Patrick Ward, a bird biologist at University of Illinois. And it’s not totally clear why.
“What I’ve noticed over the course of my lifetime is that there are fewer and fewer around,” says Brian Peer, a biologist at Western Illinois University who’s studied the species. “It’s alarming that a blackbird—the common grackle—is not so common anymore. It’s alarming that it’s declined so much.”
Some of the first observers to note the common grackles decline were birders. Participants in Audubon’s nationwide Christmas Bird Count began observing roosting sites around the country that once hosted millions of grackles were increasingly empty. Other long-term monitoring projects picked up the drop as well, Ward says, including the Breeding Bird Survey—a project that’s sent surveyors out along random country backroads since 1966, with the data analyzed by the United States Geological Survey. The data showed a 54% drop in common grackle numbers between 1966 and 2019, meaning tens of millions of grackles have been lost over the last 50 years.
“When you see big declines in a species, that’s when our lab gets involved,” Ward says.
Ward’s lab has spent the last few years trying to identify the culprit. They ruled out one possibility—that something was affecting the birds’ ability to raise young—in 2021: common grackles seem to be as successful at breeding as ever. That suggests the source of the deaths is striking in adulthood, Ward says. One likely factor is the grackles’ affection for agricultural areas, where they like to eat the seeds of crops like corn. Traditionally, that has led both farmers and state and federal governments to take a very dim view of them. In 2009 alone, the Department of Agriculture reported the intentional killing of over 4 million “blackbirds”—many of which were likely grackles—part of a pattern of similar culls going back at least as far as the 1970s.
“The U.S. Fish and Wildlife [Service] gives permits to kill some, one way or another,” Ward says, adding that it’s possible there is too much killing taking place in areas where the birds spend winter.
Another threat may come from the agricultural land itself: pesticides and antifungals. Common grackles’ affection for seed corn and their habit of spending time in fields—particularly when they overwinter in the South—means it’s possible “they’re being exposed to pesticides at rates higher than other birds and that’s leading to lower survival,” Ward says. Two years ago, his lab began putting tiny GPS trackers on common grackles in the Midwest, and discovered more than they expected were dying in fields. By the time they were able to recover the bodies, however, there was seldom enough left of the birds to determine what killed them.
One possible explanation, according to Ward, is that common grackles are caught in a flock of different problems. As migrating birds, they make an extremely physically taxing journey every year, crossing hundreds of miles between their breeding grounds in Canada and wintering grounds in the South, including Texas. If they’re being exposed to pesticides, many of those adult birds are too ill to survive the journey and the winter. And when they arrive, they’re often culled—including by gun and bombing of roosts—to protect crops.
“We don’t have the smoking gun,” Ward says. “There’s a bunch of things going on. But I think the important thing is that when you’ve got a common bird showing this huge decline, we’ve got something going on in our environment, and we need to understand what pressures are coming together to cause the problem. A few tipping points is all it takes for a population to start going into a pretty rapid decline.”
It’s notable that in Texas, great-tailed grackles—which don’t migrate, and which are mostly urban and wetland birds—are expanding their populations considerably. And while it’s possible that there’s some competition between the two species that’s putting pressure on the common grackle, it also seems that great-tailed grackles might simply be unaffected by whatever combination of stressors is killing their cousins.
Whatever the reason for the drop in common grackle numbers, it’s not just a sign of environmental strain: It threatens to carve away some of the useful ecosystem services they provide. The birds’ omnivorous diet means that they’re important predators of pest insects, and their fondness for seasonal plant-eating means that they often help move native seeds around the landscape—as well as providing prey for native hunters like hawks and owls.
“A lot of times when people worry about bird populations, you’re thinking about whooping cranes, black capped vireos, prairie chickens,” Ward says. “You don’t think about birds that used to number in the hundred millions, and dropped by tens of millions. But it’s important to think about the scale of this. If you start losing tens of millions of grackles, you start to wonder what else we’re losing.”
