Did you know: Bird Calls That Cannot be Traced by Predators
Updated: Nov 4, 2019
When danger threatens an animal, particularly one that lives in a group, it is faced with a dilemma: does it raise the alarm and thereby draw attention to itself at considerable risk or does it keep quiet risking it relatives being caught?
Since many pairs of alert eyes are more likely to spot a predator, social animals tend to rely on their fellow group-members for a warning. This is one reason why fish swim in shoals, antelopes wander in herds and birds fly in flocks. For the system to work, group animals have to play their part in detecting predators and sounding the alarm, but some animals have found a way in which to minimise the danger to themselves.
Predators find it hard to locate the black-capped chickadee’s alarm call (photo Flickr)
For a predator to locate the source of a sound, the sound must have detectable intervals or gaps, which means there must be a slight delay between these stops and starts reaching the predator’s right and left ears to know in which direction to attack.
Some birds have developed alarm calls that minimise these clues. They do this with high-pitched sounds that fade in gradually to the most intense and then slowly fade out at a wavelength shorter than the distance between their ears.
In North America, the black-capped chickadee has one of these non locatable alarm calls. When a predator approaches a flock, the birds emit their alarm calls, known as ‘high zees’ (at 8kHz) fading in and out gradually diminishing rapidly in the environment. They are just loud enough to travel to other members in the flock but no further.
Hungry Baby Robins (Pinterest)
Unlike the ’thin’ alarm call of robins to warn off hawks, that actually greets the local cat with a loud ‘tick-tick’ call, these calls are not thought to be aimed at offspring or the rest of the flock. For instance, youngsters often disperse to other flocks many miles away. The secret lies rather in the long-term monogamous mating system. Mated pairs of chickadees stay close together in the same flock with alarm calls directed at the mate protecting it from predation. That way a pair of successful breeding birds ensure that they survive together until the next breeding season.
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Reader’s Digest “Intelligence in Animals”, 1995 (viewed 21.05.2018)