Alarm Signals

Alarm Signals
Meerkats and prairie dogs are just two of the many animals that give alarm calls when they see predators. Scientists have found that many kinds of animals give alarm calls. These animals often give different calls for different predators. The animals that hear the alarms behave in different ways for each call.

Florida scrub jays take turns being on guard duty while the rest of the family group feeds. When a scrub jay sees a predator, it gives an alarm call. It makes a high-pitched scream if it sees a hawk, and a sharp cawing sound if it sees a cat. The alarm call warns other birds of danger. It also tells the predator that it has been spotted.

Little birds called black-capped chickadees also send coded alarm calls. If a chickadee sees a flying predator, such as a hawk, it makes a soft, high-pitched call. This tells other birds to hide. Other calls are used to warn of predators that are perched on a branch or on the ground. These calls warn other birds that a predator is near, and even tell them how dangerous it is.

A chickadee that sees a small owl perched in a tree, for example, adds extra “dee” sounds to the end of its “chick-a-dee” call. These extra sounds warn other chickadees that a very dangerous predator is in the area. A big owl gets one extra “dee.” This is because the small owl is quick enough to catch a chickadee, but the big owl is not; it is more likely to hunt for mice and rats.

Some mammals, such as meerkats, also communicate information about predators with their alarm calls. A meerkat on guard duty peeps quietly to let others know that everything is fine. If it sees an eagle, it gives a call that sends meerkats scurrying into burrows. If it sees a snake, it gives a call that tells other meerkats to climb trees instead. Yet another call tells other meerkats to mob a less-dangerous predator and chase it away.

Vervet monkeys, found in Africa, have one call that means a big cat, such as a leopard, is near. This call tells other vervets to climb high up into a tree. Another call means an eagle is overhead. This causes monkeys to hide in a bush or among the branches of a tree. A third call means “snake.” Monkeys stand up on their hind legs and look around carefully when they hear this call.

Other species of monkey—as well as ground squirrels, tree squirrels, and lemurs—also use different calls for different predators. Scientists have also found that one species’ alarm call may be understood by other species. Many animals flee when they hear other animals get excited or alarmed, but some animals appear to understand the details of the alarm. Little birds called nuthatches know when a chickadee’s alarm call means “little owl” and when it means “big owl.”

Not all alarm signals are calls. Alarm signals can also be seen, smelled, or otherwise sensed. An alarmed black-tail deer raises its tail and the hair on its rump. A patch of skin on its hind leg also releases a strong odor. The pronghorn, an antelope-like animal of western North America, also raises long, white hairs on its rump and releases a scent from its musk glands.

Insects also use smells as alarm signals. Pheromones are scents and other chemicals used for communication. Bees, wasps, and ants produce pheromones when they sting. The pheromones alert other insects, which come to help defend the nest. An insect called a lace bug protects her eggs and young by fluttering her wings at beetles. If her defense fails and a larva is grabbed, she produces a pheromone that warns the other larvae to flee. Likewise, an aphid attacked by a predator makes a fluid that not only clogs up the predator’s mouth, but also contains a pheromone that causes other aphids to dash away.

Underwater animals use pheromones as alarm signals, too. A sea anemone that is nibbled by a fish gives off a pheromone that makes nearby anemones close up. Many fish, such as minnows, release pheromones when a predator injures them. Fish that pick up the scent will hide or swim away.