Inquiry-Led: The Birds
The first time I saw a painting by American artist Jackson Pollock I was eight years old, standing in the Modern Wing of the Detroit Institute of Art. I wasn’t very impressed by the splatters and drips of black ink (I would have preferred more color), but I could tell the work was unconventional.
The second time I saw a Pollock original, I was a first-year college student — traversing the sidewalk just southwest of the Noyce Science Center. Again, the color palette of the work was limited: bright white and dark maroon splattered across an asphalt canvas. The paint looked fresh, as though the artist hid above me, his process interrupted by my gawking.
As it turned out, Pollock was not in the sycamore branches above my head. Nor was he the artist whose work I admired. In fact, he’d died more than 60 years prior. Instead, above me perched a cloud of approximately 60 gigantic birds. Just as I lifted my gaze, a glob of poop fell to the sidewalk, producing another Pollock-like splat. Life imitates art, no?
Their undeniable artistic gifts aside, these birds are a marvel. Year after year, large flocks return to the same few trees near the Grinnell commencement stage to pitch camp. I’ve walked across central campus just as they’ve taken flight, which has an effect not unlike that of Ozian flying monkeys. On occasion, I’ve witnessed brawls break out in the branches. Their bickering squawks are startling and, it must be said, the large birds do not scramble amongst the branches delicately. In such instances, it seems wise to get out from under the canopy ASAP.
However, in the spirit of neighborliness and my desire to please my amateur birdwatcher father, I’ve decided to get to know this population. After all, I figure that their semi-permanent residence on campus pretty much makes them honorary Grinnellians.
So, what kind of birds are these hulking poop machines? How do they produce such inspired fecal patterns? What explains their consistent return to the same home base? And what can they teach us about making a home out here in the prairie?
All this and more, in the second edition of Inquiry-Led.
Birding Basics
I mentioned that my father is an avid but amateur birdwatcher. I love to chat birds with him, but, fortunately for my purposes, Grinnell has a much more legitimate bird expert: Peter Meyers.
Meyers, assistant professor of biology, is an ornithologist — a scientist who specializes in the study of birds. As an undergraduate, I was the science community leader for Meyers’ section of the course Organisms, Evolutions, and Ecology. This entailed spending several hours sitting on overturned paint buckets in deer blinds, assisting students armed with binoculars and reminding them to Be As Still And As Silent As Possible as they identified passing birds.
I reach out to Meyers with the premise of my inquiry. All it takes is my mentioning, “that cult of large birds in the trees just south of Noyce,” and Meyers is a fount of information.
Right away, Meyers tells me that the birds are turkey vultures, Latin name Cathartes aura. He says that the birds are named not for any relation to actual turkeys, but rather for their red, featherless heads. They are, objectively, ugly. Or maybe I’m just a bad naturalist.
Meyers makes a point of explaining that turkey vultures are “new-world vultures” and “not at all closely related to old-world vultures.” To be honest, this distinction means nothing to me. I’ve never heard of new- and old-world buzzards, and I certainly don’t know the difference between the two (though I appreciate Meyers’ assuming that I would.) So, with the birds’ basic information nailed down, I decide to dig into this new- vs. old-world division. Maybe it would explain some of the striking behaviors of these birds.
“The Vulture Way of Life”
As Meyers told me, new-world and old-world vultures are not closely genetically related. Their names might indicate that the bird families are relatives that took up residence in different geographical regions, but instead, they’re a great illustration of something called convergent evolution.
In convergent evolution, two groups that don’t share a recent common ancestor evolve separately to thrive in comparable ecological conditions. They may develop similar physiological traits, similar behaviors, and similar habitats, but the traits shared between these groups are reflective of occupying and adapting to similar niches, not any genetic relationship.
In my search to understand the difference between new- and old-world vultures, I find a much-cited paper (at least, by turkey vulture academia standards) published in 1995 by The Royal Society. It opens with the sentence, “The ‘vulture’ way of life, i.e. scavenging largely on dead animals, was originally thought to have evolved only once among [daytime-hunting] birds of prey.” The paper’s authors, Ingrid Seibold and Andreas J. Helbig, go on to explain that naturalists of the late 1800s and 1900s began to note substantial differences between the new-world vulture family — the Cathartidae of warm areas of the Western hemisphere — and the old-world vultures — Accipitridae of Europe, Asia, and Africa.
For one, old-world vultures have strong feet with long talons (think: pterodactyls). New-world vultures, on the other hand, have weaker feet that they use not for grasping but to brace against animal carcasses as they tear off chunks of meat with their beaks. They’re also able to run (like a chicken) if they need to, while old-world vultures hop or flap for short distances.
One more difference between new- and old-world vultures? The new-world vultures engage in a behavior called “urohydrolysis.” What’s that? Meyers explains. “When hot, turkey vultures will defecate and urinate on their legs to cause evaporative cooling – as the moisture in their feces evaporates, it cools their legs down.” Because turkey vultures are darkly colored and absorb heat easily, urohydrolysis helps them to moderate their body temperature. It works similarly to the cooling mechanism of sweat, which absorbs heat from our body as it evaporates.
So, the hotter the bird, the more profuse the crap. Aha.
Not only does this excretory behavior set apart turkey vultures from their old-world doppelgangers, but it helps to explain the sheer abundance of fecal splats that paint the sidewalks below the vultures’ roost. And I thought sweat stains were bad.
Urine: The Hottest New Multipurpose Cleaner
Urohydrolysis, I find out, isn’t just for cooling.
The aforementioned “vulture way of life” entails birds obtaining energy by consuming the carcasses of dead mammals — known as carrion. Unlike most birds, turkey vultures have a keen sense of smell, which they use, along with their strong daytime eyesight, to locate carrion. They have absolutely humongous nostrils, which, in my opinion, can only be justified by a pretty darn good sense of smell. Otherwise, those gaping nostrils would be aesthetically and functionally inexcusable. But I digress.
Carrion is all around us, from the squirrel dead on the sidewalk of an indeterminate disease or a deer killed in a collision on I-80. For birds of prey that eat carrion, roadkill is their TV meal equivalent: manmade and readily available. It’s a large reason why turkey vulture populations are often found in proximity to human-modified landscapes. Cars = food.
Because their preferred food source is already dead, turkey vultures can save energy they might otherwise spend hunting, but they’re also exposed to the abundant and potentially harmful bacteria that colonize decaying carcasses, such as botulism and anthrax. Such bacteria-laden carrion would be a problematic meal for most animals, but it’s a dish that vultures have nicely evolved to consume: the stomach acid of turkey vultures is so strong that most bacteria cannot survive in their digestive tract. And as for the bacteria that gets on the legs and feet of vultures as they feast? Their urine takes care of it. Urohydrolysis for the win (again).
In 2015, the Iowa Department of Natural Resources (DNR) published a news release titled, “Turkey Vultures Don’t Deserve the Bad Rap.” In it, they explain how turkey vultures make an essential contribution to our ecosystem, safely eating and disposing of carcasses that might be a breeding ground for harmful bacteria in the environment. Vultures are a dead end for potentially dangerous, but naturally occurring, matter. Iowa DNR lauds vultures for their contributions to waste management and public health, and you know what? I laud them too.
A Roost of One’s Own
At this point, I’ve gained a greater appreciation for the ecological role the vultures play, and I’ve received an explanation for their artistic defecation, but I haven’t yet come to understand perhaps the most unnerving behavior of the campus vultures: their commitment to their territory.
The vultures leave their roosts each day to search for food — it’s not as though there’s a ton of carrion in Kington Plaza — but without fail, they return to that handful of trees outside Noyce. Without fail, that is, when they’re in town for the season.
According to the Audubon Guide to North American Birds, turkey vultures from the northern United States migrate long distances in the cold months, some journeying as far as South America. When it’s warm enough that carrion will not freeze, they return. Most days for the past month, I’ve been walking through campus and checking the roosting trees. It’s the first official day of spring and, so far, no vultures. Then again, it did snow four inches last week.
How do I know they’ll return? Well, turkey vultures don’t simply strike out north and establish a new home each spring. Rather, I learn, they’ll usually return to the same communal roost for most of their life. They’ll live and migrate with a large group of vultures, who will return to the same roost each year. Within the roost, most birds have their own designated place on a specific branch. Every single night, they return to that perch to sleep. Adorable. Also, Meyers tells me, if the vultures feel they or their space are being threatened, they’ll projectile vomit. Less adorable.
In this housing market, settling down is no minor decision. So how do vultures choose their roost?
You Raise Me Up on [Vultures’] Wings
I reach out to Vince Eckhart, a plant biologist and professor of biology, to ask what he knows about the trees the vultures inhabit on campus. Are they sycamores, as I’ve vaguely thought?
“You’re correct, Anika Jane,” Eckhart responds. “When the committees of vultures are on campus, they sure seem to like roosting in that cluster of American sycamores, Platanus occidentalis.”
I am going to get a good grade in tree identification — something that is both normal to want and possible to achieve.
Eckhart then offers a fascinating lesson in the nomenclature of vulture communities: When at rest in their roost, a group of vultures is a “committee.” When in flight, soaring upward in a wobbly spiral to gain a birds-eye view (ha), they’re called a “kettle.” And morbidly (or maybe endearingly?), when feasting on carrion, a group of vultures is called a “wake.” Oh, how do we name a vulture? Let me count the ways.
I’m curious if the trees themselves are significant in the establishment of a roost. Do turkey vultures have some special preference for sycamores?
Obviously, I turn to Google.
A quick search of the terms “turkey vulture roost sycamore” turns up a handful of stories from small media outlets, describing their town’s own vulture population. It’s honestly a little devastating to find that Grinnell isn’t the only college that offers a turkey vulture residential experience. First having squirrels on campus became trendy, now this??
A few searches later, and I’ve learned that, no, there is nothing special about sycamore trees when it comes to vultures. That is, there is nothing special other than their stature as relatively tall trees …
Whether they roost in a tree or a rooftop, turkey vultures need elevation. As large birds, they take flight by launching from their elevated roosts and catching warm updrafts. Their flight — and therefore their hunting — is dependent on both height and rising currents of warming air. The sycamore trees are some of the tallest and largest on campus, surviving even the reaping effects of the 2020 derecho. Not only do the trees seem to provide enough branch real estate to give each of the hundred or so birds their “own room,” they also offer an excellent launching pad for flight.
In investigating turkey vulture flight mechanisms, I stumble across a study published in Nature by researchers at the University of Georgia. Perhaps counterintuitively, this study found vulture flight is aided by human modifications of the landscape. Where natural landscapes have become home to growing human populations, paved roads and concrete surfaces retain heat from the sun and reemit it. As a result, human infrastructure produces stronger thermal currents, increasing air temperatures and assisting the flight of vultures.
The reemission of heat is a climate concern, certainly, but it turns out it benefits the birds, increasing the ease and frequency with which they can search for food. In fact, the study found, vulture populations thrive near people, doing just as well — and frequently better — in human-modified landscapes than they do in natural landscapes. Between the tall trees they’ve laid claim to and the warming effects of campus infrastructure, Grinnell’s vultures have a comfortable gig, it seems.
And, honestly, I’m not the most comfortable with this information. From the perspective of ecosystem conservationism, habitat infringement is a huge issue. Overwhelmingly, human development displaces animals, disrupting the communities and routines they’ve developed over centuries. The fact that turkey vultures thrive in proximity to our pavement and industry … it unsettles me.
But it’s also neat. And a sort of redeeming silver lining of the way we've shaped the landscape. And kind of beautiful.
For the Grinnell turkey vultures, campus is their home, perhaps even more so than it is for the students who reside here for four years before venturing onward. The birds thrive in coexistence with us, not in spite of us. And for as long as we keep things that way, they’ll return.
The vultures know something that I’m still learning: There will always be a home here.
Postscript: The final version of this story was completed on the first day of spring. Up to that point, I hadn’t yet spotted any vultures. On the next day, March 21, I walked home from work and saw a kettle of vultures circling above campus. They haven’t all returned, and their numbers will grow in the coming days, but it’s official: spring is here. Welcome home, you urohydrolizing freaks.
