This is an article from the fall 2019 issue of LSA Magazine. Read more stories from the magazine.
When a peregrine falcon attacks, watch out.
They hunt with the sun behind them, so they’re harder to see by their prey, which are most often smaller birds. Peregrine falcons often fly high into the air, then dive straight down — a move that’s called a “stoop” — tucking their wings in tight to their bodies and reaching speeds of more than 200 miles per hour, making them the fastest bird on the planet. Sometimes, they’ll brake at the end of the stoop and pull up, striking their target from below. To attack larger birds, like ducks, they ball their feet into “fists” and punch the bird at high speed, likely breaking the bird’s back so it falls to the ground.
The falcons eat the meat of the bird, leaving ripped wings, discarded heads, plucked feathers, feet, and more behind. A mated pair of peregrine falcons that lives on U-M’s campus has been discarding these uneaten prey parts locally for years, and some LSA scientists have collected the pieces for research. As a result, they not only got information on the falcons’ diets, but they also discovered data about migratory birds in the area.
A Field Guide to U-M’s Peregrines
The U-M falcons first made headlines when they began nesting in Burton Tower around 2010, high up amid the bells of the Central Campus carillon. Their presence was welcome evidence that these once-endangered birds were making a population comeback.
However, the birds’ location in the tower wasn’t ideal; summer storms would wash away their nest and eggs each year. So U-M researchers built nest boxes for the birds on North Campus and the Medical Campus, and, by 2016, the pair had hatched 21 chicks.
The birds are thriving now — the couple hatched four chicks last year: Betsy, Bursley, Markley, and Mojo. And for years now, at their old and new homes, the falcons have regularly dropped bits of prey near their nests. Some of these discarded parts have made their way to the University of Michigan Museum of Zoology (UMMZ) thanks to people like Kenneth Elgersma, a former Department of Ecology and Evolutionary Biology postdoctoral fellow.
“When I first came to U-M, I collected the remains from their breakfast several times a week. I didn’t often collect guts — they eat those. More often it was heads, beaks, feet, wings, and other inedible parts,” Elgersma says. “A few times I collected whole birds that the peregrines probably just dropped and didn’t bother to pick up.”
Elgersma and others brought the remains to UMMZ’s bird division, where professionals prepared the remains as they would any scientific sample.
“If there was meat left over, that would have been removed,” says Ben Winger, a UMMZ assistant curator. “If there was a head, someone would have removed the brains. They’re dried and prepared in the same way as other specimens in the collection.”
This includes cataloging and identifying the leftover parts. “It’s a fun challenge to figure out what the falcons dropped or what they ate from just a wing or a beak,” says Winger.
Clues about the birds’ species can be found in distinctive patterns in the feathers, or in the size and shape of the beak. “If it’s a conical heavy beak, it’s more likely to be a finch for cracking seeds,” says Winger, “whereas, say, flycatchers have a big wide beak for snagging insects out of the air.”
The “prey drops” collection isn’t huge by any stretch — the entire grouping only takes up a few drawers in one cabinet — though it is slightly unconventional. “It’s basically a set of plastic bags with parts and incomplete carcasses and labels,” says Winger. “It looks like an evidence bag in a police locker or something.”
Of course, the “prey drops” collection is only a small part of the archive. UMMZ has one of the largest research collections of bird skins and skeletons in the country, and it serves research requests from all over the world.
Pieces of the Whole
Winger says that what the peregrine falcons eat is a sample of the “diversity of birds that migrate through the area, so actually it’s an interesting window into what birds are around.”
The falcons have a strong preference for slow-flying birds like cuckoos or woodpeckers. “Cuckoos are seen by bird watchers, but not commonly,” Winger says. “So the fact that the peregrines are finding them could mean there are more cuckoos migrating through Ann Arbor than we would realize from records from bird watchers alone.”
And it’s not just cuckoos. “The falcons have caught birds that are almost never seen by birdwatchers in the area,” Winger says. “We have one, maybe two, specimens of a bird called the yellow rail, which is quite a rare bird in southern Michigan. But somehow the peregrines caught them.”
Winger adds that even though the samples in the collections are incomplete, there’s still much to learn from them. “If someone wanted to study the origin of these birds — where they were migrating from or to, for example — they can still get chemical isotopes from the feathers. If there’s any meat on the specimens at all, that would be preserved in our liquid nitrogen tank for genetic analysis. And sometimes, if the whole skull is intact, there is data there for morphological analysis.”
A morphological analysis might include, say, a comparative analysis of the peregrine prey skull against other skulls in the collection to study size differences in bird populations. Winger studies these issues in his own research. “We have done research using other collections that shows migratory birds are getting smaller and their wings are changing shape due to climate change,” Winger says. “So being able to measure the beak or the wings, even if that’s all there is, is still useful information.”
And what can you do if you find some prey drops yourself and want to turn them in to UMMZ’s collection?
“The most important thing is for people to write the date that they found it and the location,” Winger says. “That’s enough for us to get it into the collection.”
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