Interspecific Affiliation

Raymond has recently posted on interspecific grooming, and I have so much to say about this topic that I have to write about it as well—however, I look at interspecific grooming as part of the range of interspecific interactions that can occur. We’re usually not surprised when individuals of different species have agonistic interactions. However, sometimes we are surprised when affiliative interactions occur. This really shouldn’t surprise us—after all, many of us participate in interspecific interactions everyday (I probably spend more time interacting with my cats and dog right now than I spend with other humans).

Aside from my daily interactions with my best feline and canine friends (as well as observing their interactions—one of our cats does groom the dog as well), I’ve seen various types of interspecific interaction, both in captivity and in the wild.

At the Omaha Zoo, I watched a juvenile spider monkey both groom and harass the tapir with which she shared her exhibit. She groomed him, jumped on him, and eventually, in an attempt to get a reaction, reached back and grabbed his nether regions. The tapir ignored her previous actions, but did raise his head and look at her in response to that transgression. When she got a reaction, the spider monkey made a gleeful play face, and I suspect that this may have been a regular occurrence (unfortunately, I was only visiting for one day, but I would have loved to observe there more often to see if that was a regular occurrence).

At Brookfield Zoo, the spider monkeys share their exhibit with capuchins, an anteater, and a tapir. However, they seemed to largely ignore the anteater and the tapir, and would routinely harass the capuchins or redirect aggression toward them.

At Cayo Santiago, the island was teeming with both rhesus monkeys and iguanas. Most of the time, the two species ignored each other, but occasionally interactions occurred. Though they were rare, it indicated that the rhesus monkeys did see the iguanas as social actors. When the iguanas were very active during their mating season, male macaques would sometimes get irritated and chase them away. Once, I sat down on a log, and inadvertently scared an iguana hidden below it. Startled, he immediately ran out, and darted straight into my focal animal. The poor monkey was startled as well, and he indignantly threatened the iguana. However, the funniest macaque-iguana interaction is when a female macaque went up to an iguana and started grooming it. I think a friend of mine may have actually caught that interaction on tape—I would love to see it again.

During my masters research at El Zota in Costa Rica, I observed quite a bit of capuchin-spider monkey interaction. One of my focal animals, Tristan, spent a whopping 78% of his play time with capuchins! Furthermore, my male juveniles received agonism only from capuchins. In Tristan’s case, it may have been because Tristan would indiscriminately approach capuchins of all ages, and adult males capuchins responded agonistically to his solicitations. Another individual, Freddie, was far more afraid of capuchins, and was chased out of a Ficus tree several times by capuchins. I also observed one of my female focal subjects, Iris, attempting to groom a male howler—however, he seemed rather surprised by her attempts, and moved over to rest a meter away from her.

During my dissertation, I observed a few more interspecific interactions. During my pilot project during the summer of 2008, we observed an adult male howler playing with a juvenile male spider monkey, as well as an adult female spider playing with an adult female howler. During the main portion of my dissertation fieldwork, adult female focal Agata fought with, and then was chased by an adult male male. Subadult female Anne groomed an adult male howler for less than a minute before he retreated. Another time, Anne solicited play from an adult female—they played for less than a minute. Juvenile male Judah played with an adult male howler for quite some time—I unfortunately was not able to note the duration of their play encounter, because I was doing focals on Judah’s mother, Jlo, at the time. I also observed adult female Strawberry chased an adult female howler—I wrote in my notes that it was a “slow chase.”

I have also heard reports that someone observed spider monkey-capuchin grooming interactions--I'm very envious, because in all the time I've spent with those spiders, I have not seen it! I've heard there is photographic evidence, but I have yet to see the picture. This summer, an instructor with a primate class also observed a subadult male capuchin mounting a subadult male spider--and got a picture of it (I did see that photo!).

Why do these interspecific interactions occur? Most agonistic encounters can usually be understood in the context of feeding competition. However, interspecific affiliation, particularly grooming and play, are a bit more difficult to understand. I think it indicates that many primate species recognize other primate species, as well as other animals, as social actors. Play among different primate species is more commonly observed, and may just be a consequence of playful juveniles looking to play with whoever will play with them, regardless of species. This might be especially valuable for juvenile spider monkeys—small subgroups can limit their opportunities to play with conspecifics, and adults may be busy feeding, resting, or grooming with other adults. However, play among adults of different species, and interspecific grooming, is another issue. Why would adults invest time in affiliating with another species, when they could be investing in relationships with conspecifics? In species that form interspecific associations, it makes sense to invest in relationships with the other species. For other species, its less clear.

How can we study this phenomenon? Unfortunately, because such interactions tend to be infrequent, we usually just collect anecdotes as we collect data for another project. However, perhaps collaborative effort on examining collections of observations might yield some interesting insights. Also, there are a number of zoos that house multiple species together, and these exhibits probably are the best place to specifically exam these questions. However, just because animals are housed together does not mean that they will affiliate together—the spiders and capuchins at Brookfield Zoo are a good example of that. It may also be valuable to study interspecific affliliation among species that frequently form interspecific associations, as the frequency of interactions would likely be more common.

Have you observed any interesting interspecific interactions, or have any ideas or insights into why it occurs? Please share! And I you have observed interspecific grooming, please let Raymond know as well!