February 23, 2009
Those adorable little meerkats aren’t just good TV fodder—they’re great research fodder as well.
A couple of University of Zurich scientists, publishing in the March issue of the American Naturalist, studied alarm calls produced by meerkats and Cape ground squirrels that lived sympatrically on the Kalahari Desert.
Alarm calls produced by animals come in two flavors: One type denotes only a level of urgency, while the other includes information about predator type and how individuals should respond (“functionally referential” signals). Theories of how these alarm calls evolve have suggested that the type of alarm call used by a species is influenced most by how it responds to threats. Species that use different strategies for escaping different predators, logically enough, would be best served by functionally referential signals. But creatures that use a single strategy would need only the urgency level in their alarms.
The meerkats and Cape ground squirrels, though, respond in a similar fashion to threats—they run for cover, escaping down bolt holes into burrows that the two species often share. The Cape ground squirrels use the urgency-dependent alarm calls, as would be expected by the theory, but the meerkats use functionally referential signals. Why the difference?
The Cape ground squirrels eat vegetable matter that they can find close to home, while the meerkats have to venture farther for their meals of insects and other small animals. The Cape ground squirrels don’t lose much by retreating to their burrows, because they aren’t that far away. The meerkats, though, can’t run home every time they’re threatened, because the cost would be too high (lost yummies). They respond differently to different threats (such as by moving away from an ambush predator like a jackal instead of returning all the way to the burrow and trying to wait the jackal out). In addition, the meerkats have to be able to respond in the same way to a threat, because if one runs in the opposite direction of the group, he could be toast (single meerkats and small groups have a higher likelihood of being eaten by a predator).
This video (meerkats responding to the “threat” of an ultralight plane flying above) comes from YouTube user nyatnagarl who has made many videos of the meerkats at the Hanover Zoo in Germany and has noticed:
The meerkat group react[s] quite differently to the aerial encounters made in this location:
* Passenger jet planes high in the sky – usually ignored, but at sunset, when they are caught and illuminated in the sky by the last rays of the sun, they are watched closely, but an alarm is never raised.
* Small propeller planes (Cessna, etc.), low flying – sometimes completely ignored (i.e., not even the head is raised), sometimes watched. Since there is a small airport nearby, they know these planes very well, and understand they pose no danger. In general the sound of the classic piston engine aircraft is associated with “not dangerous”, you can often hear an engine drone in parts of the videos I have posted.
* Anything that has a triangular shape like hang gliders, ultralights – will usually cause an intense warning. It is worse when the flying object is silent (like hang gliders) – this will usually cause an at least partial retreat of the family into the burrow. A silent slowly moving object with swept wings probably reminds them most of a predatory bird.
* Hot air balloons – they do not like these at all. Although they are usually distant, the silent, looming presence on the horizon seems to disturb the meerkats deeply. They will usually watch these intently and most activity will cease until they disappear.
* Zeppelins – we don’t get these very frequently but when the “Zeppelin NT” flew over the enclosure at low altitude one afternoon it was considered the ultimate enemy. The meerkats raised alarm, disappeared into the burrow and did not reappear for the rest of the day!
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