Late one September many years ago, I was visiting Pointe Mouillee State Game Area at the mouth of the Detroit River along the western shoreline of Lake Erie in late September when I looked skyward and saw the most stunning example of fall bird migration I have ever witnessed.
Hundreds of broad-winged hawks were soaring, lazily, round and round in a huge flock about a quarter-mile high. Then, it was as if an invisible hand reached into the swirling flock and began drawing the raptors away a few at a time. Over the course of the next half-hour or so, all of the hawks gradually left the flock and disappeared from sight, heading southward in a long line like a string slowly being pulled off a rotating spool of thread.
Red-tailed hawks are the most widespread, most common, and most commonly seen raptor in North America
The vivid image of that annual autumnal spectacle of migration remains in my mind’s eye yet today. But it has always made me stop and wonder: Why do some raptors migrate, while others don’t?
Kevin McGowan, who hails from Springfield, has been studying the question and others like it for a long time. He holds two degrees in zoology from Ohio State University and is now a professional ornithologist and educator with the prestigious Cornell Lab of Ornithology at Ithaca, New York. “I’ve been a birder since junior high school,” he says. “I grew up birding with the Clark County Audubon Society.”
He’s studied bird migration for years, and if anyone knows the answer to my nagging question, it’s McGowan. “For raptors, it’s all about finding food,” McGowan says. “If they can find enough food in their location year-round, they don’t migrate. If they can’t, then they must move.”
Of course, that also raises another question that’s just as fascinating as why some species of birds migrate and others don’t, and that is: How do they migrate? How do they know where they’re going — especially young-of-the-year fledglings? And how do they navigate during those arduous, dangerous, twice-per-year journeys north and south over hundreds if not thousands of miles? Some of the most recent bird migration research is revealed in author Scott Weidensaul’s latest book, A World on the Wing, which includes this fascinating tidbit:
When a bar-tailed godwit takes off from Alaska and flies across the widest part of the Pacific (a journey, research shows, that can take 11 days of nonstop flight), sleep obviously becomes an issue. A sleeping bird can’t fly; flying is not an autonomous function like breathing. Birds get around this problem through [big-word alert] unihemispheric sleep — putting one half of their brains to sleep for a few seconds at a time, alternating endlessly back and forth.
The avian world, like all of nature, is simply amazing…and likely even more so than we yet fully realize.
Three Migrating Raptors
Red-tailed hawk
According to McGowan, red-tailed hawks are the most widespread, most common, and most commonly seen raptor in North America. In Ohio, there are both resident and migrant populations of redtails — resident redtails remain in the state all year, breeding here, but the migrant redtails breed in Canada and return to the Buckeye State only during the winter months. “Again, it’s all about finding food,” he says. “For redtails as a species, food is generally easier to find in Ohio than Canada during the winter.”
Gyrfalcon
In contrast to red-tailed hawks, the gyrfalcon — the world’s largest falcon — is found in the highest latitudes of the Arctic tundra all across the Northern Hemisphere, where they feed on ptarmigans, a grouse-like bird. “Most of those birds spend the entire winter in the high Arctic in the dark and extreme cold, only occasionally migrating to southern Canada and the northern U.S.,” McGowan says.
Broad-winged hawk
McGowan confirmed that my encounter long ago with migrating broad-winged hawks, a common forest hawk of eastern North America, wasn’t just some fever dream. “They completely leave their breeding ground in the U.S. and Canada in the fall, migrating to South America for the winter,” he says. “They migrate in groups ornithologists call ‘kettles,’ made up of hundreds, sometimes thousands, of hawks.” He says the birds stage at locations conducive to migration, but don’t all ultimately end up in the same place in South America. “Broad-wings seem to get something social out of clustering together, but it’s a behavior we don’t yet totally understand.”
