Complex relationships between species such as birds and grazers are common, but often unrecognized by over-simplified wildlife management theories. As a result, wildlife managers routinely attack species whose interdependence we do not understand. For example, in Texas, tax policy rewards landowners who attempt to eradicate brown-headed cowbirds, a species that has existed symbiotically with bison (and cattle) and other bird species, for countless millennia.
Magpies will eat ticks that drain the blood from elks, but a scientist found it takes the right mix of elk-magpie personality for the relationship to work.
Chances are that’s a shy elk looking back at a bold magpie, in the photograph above.
They get along, so to speak, because the elk needs grooming and the magpie is looking for dinner. But they may have never entered into this partnership if it weren’t for their particular personalities, suggests a study published Wednesday in Biology Letters.
Let’s start with the elk. In Canada’s western province of Alberta, they’ve been acting strange. Some have quit migrating, opting to hang around towns with humans who protect them from predators like wolves. Others still migrate.
As a doctoral student at the University of Alberta, Robert Found, now a wildlife biologist for Parks Canada, discovered over years of observing their personalities that bold elk stayed, while shy elk migrated. But he noticed something else in the process of completing his research: As elk laid down to rest at the end of the day, magpies approached.
There appeared to be a pattern: elk of some personality types aggressively rejected magpies. Others didn’t. “Sometimes the magpies will walk around right on the head and the face of the elk,” Dr. Found said.
Scientists define animal personality by an individual animal’s behavior. It’s predictable, but also varies from others in a group. Dr. Found created a bold-shy scale for elk, measuring how close they allowed him to get, where elk positioned themselves within the group, which elk fought other elk, which ones won, how long elk spent monitoring for predators and their willingness to approach unfamiliar objects like old tires, skis and a bike. He also noted which elk accepted magpies.
To study the magpies, he attracted the birds to 20 experimental sites with peanuts on tree stumps. During more than 20 separate trials with different magpies, he judged each bird’s behavior relative to the other magpies in a trial. Like the elk, he measured flight response, social structure and willingness to approach items they hadn’t previously encountered (a bike decorated with a boa and Christmas ornaments). He also noted who landed on a faux-elk that offered dog food rather than ticks (a previous study showed magpies liked dog food as much as ticks).
Bolder elk and magpies exhibited riskier behaviors like tolerating the experimenter, approaching novel objects and fending off animals. About half of the elk let magpies land, and just over half the magpies landed on the fake elk. And it was the shy elk and bold magpies that were more likely to engage.
This was counterintuitive for an elk: eyeballs offer easy targets for hungry magpies. But magpies also eat winter ticks.
This tick species waits on tall grass for passing animals, like elk and deer, but preferably moose, which don’t notice them until it’s too late. They clump together and infest by the thousands, remaining on a host all winter, expanding to grape size when fully engorged. They can drain all the blood from a moose calf, and are credited with giving the moniker “ghost moose” to those that groom themselves hairless.
Elk have fewer winter ticks than moose, perhaps because they’ve had more time to evolve coping mechanisms, like habitual grooming. But hair loss around the neck is still a problem.
Two decades ago, Bill Samuel, a retired moose biologist and author of a definitive book on moose and winter ticks, foundsome moose also evade the pests by tolerating magpies. Perhaps, Dr. Found thinks, shy elk gain an advantage over bold elk and compensate for their bashfulness by accepting magpies.
Few studies have examined the role that personality plays in shaping interactions between species, especially mutualistic interactions. In one study, however, aggressive spiders in so-called mutualistic relationships suffered compared to docile spiders. And in another study, bold cleaner fish tended to cheat mutualism by consuming the protective mucus around their client fish and swimming off instead of eating parasites. Dr. Found thinks personality reveals a messier mutualism than once assumed.
But there’s a missing piece to this puzzle, said Alison Bell, who studies personality in fish at the University of Illinois, Urbana-Champaign. This could be a three-way relationship: What’s the tick’s role? Does tick personality factor in? And does this behavior extend to all elk and magpies, or is it just some western Canadian quirk?
While more research remains to be completed, Dr. Found’s peculiar observation, described for the first time, demonstrates the complex role personalities play in the animal kingdom. Whether emotional concepts or just behavioral tendencies, personalities exist in all kinds of species and can influence the interactions among and between them. Some combinations work; some don’t. In this case, opposites attract — and it seems to be working.