Crows removing ticks: helpfulness, opportunism, or something else?

Guest post by Thom van Dooren

If you’ve spent much time at all watching YouTube videos of corvids, you’ve likely come across some of the numerous examples of them engaging in the seemingly helpful act of removing ticks and other ectoparasites from all kinds of other animals. The lucky ‘client’ might be a rhino, a sambar deer, or a cow.  Admittedly, it isn’t always entirely clear that these crows are being exclusively helpful, engaging in what biologists call symbiotic cleaning. In at least some of these cases, there seems to be a reasonable chance that they’re (also) playing, pestering, or even getting ready to take a bite out of an unsuspecting animal. 

In a few cases though, the results of their cleaning work speak for themselves. One recent set of camera trap videos circulating at the moment on social media shows a group of corvids, probably Torresian Crows (Corvus orru), removing ticks from several, somewhat reluctant, wallabies. The ticks have been around for a while, as evidence by their size, and cover large parts of many of the animals’ ears and necks. As the wallabies arrive at a watering station that has been set up for them in the dry summer of southern Queensland, the crows move in. They carefully sidle up to the wallabies while they’re drinking, and then, in one swift movement, a beak flashes out and returns with a tasty, protein-rich, tick.

While these videos fascinate, delight, and frequently disgust, YouTube viewers, these behaviors are not uncommon in the animal kingdom. Symbiotic cleaning, across species lines, is a particularly common practice for fish, crustaceans, and birds. The animals who receive these cleaning treatments are mostly larger fish and herbivores. In the case of corvids, studies have documented the symbiotic cleaning of deer, wild boars, camels¹, and a handful of other species.

Perhaps my favorite example—sadly, one without footage—is another Australian case involving the same species, the Torresian Crow. At the top of the Northern Territory, on the Cobourg Peninsula, these crows have struck up an unlikely relationship with banteng (Bos javanicus), a species of feral cattle that was introduced to Australia in 1849. Over the last couple of decades, scientists have observed crows landing on the backs of resting banteng. The banteng will then roll onto its side and lift its upper legs—which is not a comfortable or easy posture for a banteng—so that the crow can access the area under the legs and belly. Moving into this space, crows have then been observed removing ectoparasites, likely ticks, from these exposed areas. 

While this kind of cleaning is not in itself exceptional, the degree of attunement between the cleaner and the client in this case is fascinating. In many cases, as with the wallabies, the clients seem not to agree to the treatment at all. In other cases, as in a beautiful set of photos of a house crow cleaning a cow in India, we can see some degree of ‘posing’ and positioning to facilitate access. But in the case of the banteng and the crow, a whole procedure seems to have been worked out and agreed to. Torresian crows aren’t known to have similar relationships with any other mammals, and banteng around the world aren’t known to deliberately expose themselves for grooming by any other bird. Yet this is happening here. We will never know which crafty individuals struck up this mutualism, how those first awkward interactions took place, how a proposal was made, and how an agreement was reached that such vulnerability was worth the risk. But we do know that this behavior is spreading as more and more banteng and crows around the region get in on the action.

There are lots of lessons that might be taken from all these inter-species interactions. One that particularly interests me, visible in the comments below many of these YouTube videos, is the desire to cash this behavior out in simple, black and white terms. Either this cleaning is an example of a helpful altruist, or it is a nasty, opportunistic, crow taking advantage of another. Biologists, too, are not immune to these kinds of explanations—although which ones are preferred does shift over time, as things like ‘selfish genes’ go in and out of fashion. As Robert Poulin and Alexandra S. Grutter noted, writing in the mid 1990s: “Over the past few decades … the opinion of scientists regarding cleaning symbioses has changed, from selfless cooperation, to a mutually beneficial interaction, and finally to a one-sided exploitation.”

Of course, how these interactions are characterized depends a lot on whether we’re after the adaptive, evolutionary, explanation, or the psychological motivations of the individual involved. When it comes to clever corvids, there seems no reason to assume that all individuals engage in this behavior for the same proximate reasons. Some Torresian Crows might clean wallabies or banteng purely for the tasty snack. But can we hold open room for the possibility that others might, at least in part, be motivated also by the desire to help out, to remove a difficult parasite? As I’ve argued elsewhere, I want explanations that, at the very least, refuse to rule out in advance the possibility that corvids might be engaged in something like “targeted helping” across species lines. More than this, I think we need explanations that refuse one size fits all, black and white, options.

When it comes to the ethical behaviors of humans, many people have likewise often looked for either/or explanations, altruism or selfishness. But for hundreds of years at least some philosophers have been arguing for the need to destabilize these categories. When we look closely, our own actions are very rarely purely selfless or selfish, they are a complex, shifting, sea of grey. Perhaps it is time to recognize that similar, even if thoroughly distinctive, dynamics might be at work in the black and white worlds of corvids and other nonhuman animals?

Thom van Dooren is a philosopher and a corvid enthusiast. His most recent book is The Wake of Crows: Living and Dying in Shared Worlds (Columbia University Press, 2019). He is an associate professor and Australian Research Council Future Fellow at the University of Sydney and a Professor II at the University of Oslo. www.thomvandooren.org

You can read an excerpt of Kaeli’s review of The Wake of Crows for the journal Oryx here.

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Literature cited
¹Lewis, A. D. (1989). Notes on two ravens Corvus spp. in Kenya. Scopus, 13.2, 129–131.