Friday biology: Oxpeckers clean a rhino

January 13, 2023 • 1:15 pm

The news is thin and what there is is depressing, including Russian claims that it’s captured the tiny salt-mining town of Soledarin in Ukraine. Although the town isn’t of strategic importance, it’s of propagandistic value to Russia, which has been losing battles left and right. (Kyiv denies that the Russians have the town.)

But let’s forget the news for a minute and watch a nice, short video of animals helping each other instead of killing each other. In this case we have a mutualism, a behavior involving interaction between two species in which each individual reaps a benefit. In this case it’s between a black rhinoceros (Diceros bicornis) and red-billed oxpeckers (Buphagus erythrorynchus).

Remember that for the behavior to have evolved on both sides (pecking and tolerance of pecking), the benefits can’t just be food and cleaning, but somehow those behaviors must have enhanced the reproductive output of individuals in each species (i.e., what used to be called “fitness” before the ableists tried to erase the term).

Note that the birds clean the ears, the lips, and even between the toes!  They clean not only wild mammals, but also domestic ones like cattle.

You might imagine, as I do, that this mutualism began with evolution in the bird, perhaps a tendency to eat insects wherever it can find them, which would already be built in by selection to get food. Over time, the boldest birds, with a genetic tendency to be braver than other birds about foraging on large, intimidating mammals, might propel the evolution of a tendency to seek those mammals out.

But of course, if it’s a true mutualism, the mammals also have to evolve tolerance of a bird pecking away at their bodies.  Have they? Well, you could in principle test whether tolerance has evolved by mimicking the pecking of a rhino with something else, but that really wouldn’t tell you the answer, for the evolution might have been to “tolerate stuff that feels like pecking”. Besides the experiment would be dangerous!

But if the rhino has evolved tolerance, that means that those rhinos who let themselves be cleaned left more offspring than those who didn’t—assuming there were genes promoting more or less tolerance. That kind of genetic variation isn’t hard to imagine, since there’s genetic variation for almost any behavior. And since insects like ticks and flies can carry parasites, it’s also easy to imagine that a peck-tolerant individual would leave more offspring than other individuals who drive away the cleaners.

10 thoughts on “Friday biology: Oxpeckers clean a rhino

  1. Ah delightful – the perfect antidote to the language perfidy – Nature!… red in tooth and claw, true, but also clean behind and _in_ the ears!

  2. Interesting biology!

    FWIW, I will continue to use the word “fitness.” It has been in use for 100 years, has a well-defined technical meaning, and permeates the literature. Using something else would isolate future evolutionists from the history of the field for no good reason, and fitness is a perfectly good word.

    You’ll note that I used that other verboten word, “field,” as well. Another perfectly good word.

  3. Why is the common name “ox pecker” and not “rhino pecker”? Were they first observed pecking on oxen? Of course either way it brings to mind something entirely different…

    But these types of interactions are interesting. Crocodilians, many ocean fish and sea turtles engage in similar activities, and they are more amazing since the animals being cleaned could easily snack upon the cleaners.

    But, even more interesting, and complete 180 from peckers of any kind…did anyone see the article about the discovery that female snakes have a clitoris? Well, a hemiclitoris, anyway. It was mentioned at the end of the most recent Herpetological Highlights podcast. Crazy to think it took so long to find (cue the lame jokes).

  4. Is there a way to tell if the behavior is culturally learned instead of evolved?
    I am sure that question has been asked by others, was just wondering about the method(s).

    1. I was wondering the same thing. These are reasonably intelligent animals. I don’t believe this would necessarily need to be evolved instinctive behavior on either side, it could be learned.

    1. EXCUSE ME? You use one example of oxpeckers injuring a debilitated giraffe to blithely declare that “nowadays they are considered parasites”? And that the mutualistic view is outdated?

      One video on YouTube is not evidence to overthrow the mutualism theory, which, by the way, has data to support it. Why don’t you look at some data?


      I’d say that outweighs video and your personal view of what the field thinks.

      The question is whether IN GENERAL, oxpeckers raise the fitness of the mammals they groom. One exception doesn’t overthrow that.

  5. I took Mohamed Noor’s online class intro to genetics and evolution several years ago. The oxpecker was an example of an incorrectly presumed optimality. The oxpecker was thought to help large mammals by picking off ticks. A study in 2000 (I don’t have source; this is from my class notes) found that the number of ticks was not reduced on animals with the birds; and the birds were enlarging open wounds and drinking blood. It turns out the animals (e.g. rhinos) tried to get rid of the birds but couldn’t.
    The report about oxpeckers cleaning the ears of rhinos may be a different story, but I was impressed by the example in the class, of making incorrect assumptions about mutual benefit.

  6. Just to be as picky as an oxpecker, ticks are not insects. We enjoyed watching them routinely on a wide variety of mammals big and small in Kruger National Park in South Africa last month, but did see a couple of instances where they appeared to be pecking at open wounds. There could be some “cheating” going on in the relationship. Indeed the wide variety of mammals they forage on either implies repeated evolution of tolerance in these mammals (not impossible), or simply adventurous foraging by the birds.

  7. Off Topic, but I heard that Dr. Harriet Hall of Science Based Medicine has died. She was probably the only one keeping Science Based Medicine from becoming Ideology Based Medicine.

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