In Robert Gardner’s documentary film Dead Birds, the men of a highland New Guinea village guard the perimeter of the territory, watchful for men of the neighboring group who may be intent on sneaking into the gardens to capture and kill an unwitting child or woman in order to avenge a prior death. But they don’t see the men sneaking through the dense riparian forest. They don’t even look for them. Rather, they see the birds fly from their preferred habitat where they are foraging or resting, startled into the open by … something. The birds belie the predator.
Today, in construction related traffic out west of the twin cities, I saw a Columba livia, aka pigeon, flying frantically across my path. Pigeons often look frantic, but this one was actually doing evasive maneuvers. Another pigeon nearby was doing the same thing, and it was not flying in parallel with the first. And a third a ways away had yet a third vector of flight. Flocking birds fly in parallel. Frantic birds do not.
So my eyes traveled to the point from which the birds may have diverged, and there was a fast flying, powerfully flapping raptor. My first thought was Falco peregrinus, the peregrine falcon, because they are big, fast, and eat birds. But after a brief moment I recognized the fluttering moth-like flight of Accipiter gentilis, the northern goshawk. Having no chance of catching up to the pigeons, the goshawk turned towards a lone tree that I always check on passing for raptors, as this is the territory of a pair of Buteo jamaicensis we have been watching for years. Just as the goshawk flew into the canopy, the canopy emptied out like a country western bar at 3:00 AM when the sheriff deputies arrive to break up a fight. Only instead of drunk cowboys it was blackbirds and sparrows which had been hoping no one would notice them, piling out of that place.
(On the way back, a half hour later, Accipiter gentilis was perched on a branch in that very tree, munching on … something with feathers.)
In the Semliki Valley, when I was looking into the behavior of large carnivores and their eating habits and landscape movements, the same principle applied. Drive up to a herd of antelope (in this case, Kobus kob thomasi, the Ugandan kob) and they all stare at you, except three or four who are the farthest away. They are all staring at something else. Kill the engine and sit tight for 20 minutes. Over time, the kob will increasingly ignore you, and more frequently glance in a certain direction, most of them looking the same way. Now you know where gimpy old Uncle Elmo’s remains lie scattered in the tall grass, two or three well fed lions napping in the nearby shade.
For years we have known that monkeys pay more attention to each other’s reaction than to potential threats, under certain circumstances. Indeed, the efficacy of responding to another individual who is not a predator rather than only to predators is so marked that alarm calls have evolved in many species. Alarm calls presumably put the alarm caller at risk. A predator that elicits the call response may well have not noticed the caller, but now, there is no doubt that something to eat is nearby. Of course a well placed alarm call can also signal that the potential prey is on to the predator’s approach, and will thus put the predator off. But the conventional wisdom is that alarm calling has a cost, so it must therefore have a benefit. That benefit has to be realized via kin selection, whereby relatives benefit even if some die warning others. And, once alarm calling gets going, it can play a role interspecifically, with one species gathering information by observing the behavior, including the alarm calls, of another.
A recent study by Kitchen, Bergman, Cheney, Nicholson and Seyfarth (most of you will recognized Cheney and Seyfarth as big kahunas in the primatology world) demonstrates a good example of this. One question they explored is this: Is the reaction towards the alarm calls of a different species something that is mainly encoded in the genes or something that involves more social learning?
To examine whether familiarity and/or shared vulnerability with the calling species might influence the ability of sympatric species to distinguish heterospecific alarm calls, we tested whether four ungulate species (impala: Aepyceros melampus; tsessebe: Damaliscus lunatus; zebra: Equus burchelli; wildebeest: Connochaetes taurinus) could distinguish baboon (Papio hamadryas ursinus) alarm calls from other loud baboon calls produced during intra-specific aggressive interactions (‘contest’ calls). Overall, subjects’ responses were stronger following playback of alarm calls than contest calls. Of the species tested, impala showed the strongest responses and the greatest difference in composite response scores, suggesting they were best able to differentiate call types. Compared with the other ungulate species, impala are the most frequent associates of baboons. Moreover, like baboons, they are susceptible to both lion and leopard attacks, whereas leopards rarely take the larger ungulates. Although it seems possible that high rates of association and/or shared vulnerability may influence impala’s greater ability to distinguish among baboon call types, our results point to a stronger influence of familiarity.
So, even a basic and widespread mammalian trait is shaped by experience. This should help, a little, to calibrate one’s thinking on such matters when it comes to assertions that different groups of humans have genetically determined differences in ability.
The research in this paper (Comparing responses of four ungulate species to playbacks of baboon alarm calls) does have a confounding problem, which the authors recognize: Impala’s ‘get’ interspecific calls better than, say Zebras. But they may also be more vulnerable to predators (for a number of reasons). Selection on this ability may simply be stronger for them.
So, remember this: Next time you are walking to the store and you see and hear a murder of crows which seem focused on a certain large and well flushed tree, don’t think “Noisy Corvus brachyrhynchos.” Rather, think “Ah … Bubo virginianus…”
Kitchen DM, Bergman TJ, Cheney DL, Nicholson JR, & Seyfarth RM (2010). Comparing responses of four ungulate species to playbacks of baboon alarm calls. Animal cognition PMID: 20607576