Barn owl nestlings recognise their siblings' calls

Barn owl nestlings

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Barn owl nestlings recognise their siblings' calls, according to researchers.

Instead of competing aggressively for food, young barn owls are known to negotiate by calling out.

A team of scientists in Switzerland discovered that the owlets have remarkably individual calls.

They suggest this is to communicate each bird's needs and identity in the nest.

The findings were announced in the Journal of Evolutionary Biology by Dr Amelie Dreiss and colleagues at the University of Lausanne, Switzerland.

Barn owls (Tyto alba) are considered one of the most widespread species of bird and are found on every continent except Antarctica.

An average clutch size ranges between four and six eggs but some have been known to contain up to 12.

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Previous studies have highlighted how barn owl nestlings, known as owlets, negotiate with their siblings for food instead of fighting.

While their parents search for food the owlets advertise their hunger to their brothers and sisters by calling out.

"These vocal signals deter siblings from vocalizing and from competing for the prey at parental return," explained Dr Dreiss.

"If there is a disagreement, they can escalate signal intensity little by little, always without physical aggression, until less hungry siblings finally withdraw from the contest."

To understand more about about this communication, researchers studied wild owls living in nest boxes in western Switzerland.

Based on recordings, the scientists estimated that a single nestling makes up to 5,000 calls a night in the absence of its parents.

They suggested that the probability of the chick making false signals is low because it is an energetically costly activity.

Earlier this year another member of the research team, Prof Alexandre Roulin, revealed that the owlets do not interrupt each other's calls and that they eavesdrop on calling contests as part of this negotiation for food.

In their latest study, Dr Dreiss and colleagues recruited students to listen to the recorded calls of owl chicks.

The students were able to tell the difference between owlets' calls by ear, suggesting that the birds had individual voices that made them identifiable to nest mates.

Further analysis of the calls revealed that they varied depending on the owlet's family, age and sex, as well as how hungry they were.

Dr Dreiss suggests this shows that sibling rivalry has promoted the evolution of individual voices amongst barn owls.

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