troop

A pigeon taken hundreds of kilometers from its loft in total darkness will nevertheless depart almost directly for home when it is released. The nature of this map sense remains one of ethology's most intriguing mysteries. Honey bees also exhibit excellent communication abilities. A foraging bee returning from a good source of food will perform a waggle dance on the vertical sheets of honeycomb. The dance specifies to other bees the distance and direction of the food. The dance takes the form of a flattened figure 8; during the crucial part of the maneuver the forager vibrates her body. The angle of this part of the run specifies the direction of the food: If this part of the dance points up, the source is in the direction of the sun, whereas if it is aimed, for example, 70° left of vertical, the food is 70° left of the sun. The number of waggling motions specifies the distance to the food. The complexity of this dance language has paved the way for studies of higher animals. Some species are now known to have a variety of signals to smooth the operations of social living. Vervet monkeys, for example, have the usual set of gestures and sounds to express emotional states and social needs, but they also have a four-word predator vocabulary: A specific call alerts the troop to airborne predators, one to four-legged predators such as leopards, another to snakes, and one to other primates. Each type of alarm elicits a different behavior. Leopard alarms send the vervets into trees and to the top branches, whereas the airborne predator call causes them to drop like stones into the interior of the tree. The calls and general categories they represent seem innate, but the young learn by observation which species of each predator class is dangerous. An infant vervet may deliver an aerial alarm to a vulture, a stork, or even a falling leaf, but eventually comes to ignore everything airborne except the martial eagle.

One fascinating aspect of some animal societies is the selfless way one animal seems to render its services to others. In the beehive, for instance, workers labor unceasingly in the hive for three weeks after they emerge and then forage outside for food until they wear out two or three weeks later. Yet the workers leave no offspring. How could natural selection favor such self-sacrifice? This question presents itself in almost every social species.