Definition
An alarm call is a survival signal. An animal that spots a predator or other danger first makes a sound to warn the animals around it. The caller risks giving away its own position, but it greatly raises the odds that the whole group survives.
A signal that risks one to save everyone
Think of a fire alarm ringing through a whole building when a fire breaks out. Animals do something similar and call at the top of their lungs when a predator appears. Picture a squirrel or a meerkat letting out a sharp cry when a fierce hawk shows up in the sky. Hearing it, the others dash into rock crevices or underground burrows and save their lives.
But the animal that made the sound is in serious danger. Its sharp call pulls the predator's eyes and attack toward itself. So why hasn't this risky behavior died out? It harms the caller, yet it has kept going.
The best-known explanation comes from who lives nearby. In species like ground squirrels, where females stay close to where they were born, many of the neighbors are parents, siblings, and offspring. They are family who share the caller's genes.
Even if I risk getting caught, if several of my blood relatives survive, more of my genes get passed to the next generation. Biologists call this kin selection (helping family so your own genes get passed on). A 1977 study of Belding's ground squirrels supported this idea. Other explanations are also being studied, though, such as distracting the predator or telling it "I've already seen you."
Different predators get different calls
An animal's alarm call is not just a startled scream. The pitch and rhythm change in fine detail, depending on which predator is coming and how it is approaching.
A well-known example is the vervet monkey of Africa. These monkeys make completely different calls for a leopard, a snake, and an eagle. Each call carries a different meaning, so the other monkeys react differently to each one.
When the leopard call rings out, the monkeys run to the tips of high branches that a leopard can hardly climb. When they hear the eagle call, they dive into thick bushes to hide from the sky. When they hear the snake call, they stand up on two legs and look hard at the grass on the ground.
So an alarm call is more than noise. It works like a secret code that instantly passes along the right action for the situation.
To be more precise
Alarm calls are not always a kind, honest signal meant for friends. In nature, some animals cleverly use them to cheat.
A bird called the fork-tailed drongo, which lives in southern Africa, gives a fake alarm call when a meerkat catches a tasty meal. The startled meerkat thinks a predator has appeared and bolts into its burrow. In that moment, the drongo swoops in and steals the abandoned food.
Also, the audience for an alarm call is not always friends. Sometimes the call is aimed at the predator, to say "I've already spotted you, so your ambush has failed." This works as a way to discourage the hunt.
A predator whose ambush has been exposed often gives up the hunt so it doesn't waste energy. In the end, an alarm call is not only a sacrifice to protect the group. It is a strategy that holds many survival skills, including fooling others and driving off enemies.
Common misconceptions
An alarm call is always a purely selfless act of sacrificing yourself for the group.
It may rest on an evolutionary calculation to protect family genes, and it is often used as a strategy for the individual's own gain, such as a fake alarm call that steals someone else's food.
Where you meet it
Vervet monkeys tell an eagle in the sky from a leopard on the ground and make a different alarm call for each.
Drongos sound a fake alarm call to make meerkats run away, so they can steal the meerkats' food.
In one sentence
An alarm call is a finely tuned survival signal that warns of a predator, protects family, and helps others respond the right way.