Swans wake up and choose violence, forgoing rest in favour of aggressive behaviour

Swans will cut down on resting time to engage in aggression, according to a study published in PLoS One.

Based on webcam observations of mute (Cygnus olor) and whooper (C. cygnus) swans in a Scottish reserve, the research found that both types of bird will sacrifice resting in order to spend more time behaving aggressively.

“These swans use aggression if there’s competition over foraging areas,” says co-author Dr Paul Rose, a researcher at the University of Exeter, UK, and Wildfowl & Wetlands Trust. “Our findings show that this requires a trade-off, and that both species reduce resting time to allow for this aggression.”

The researchers also tracked swans’ time spend foraging for food, and “maintenance” – preening and oiling feathers.

While rest and aggression was the strongest trade-off, the researchers also found the swans would sacrifice rest in favour of foraging.

Mute swans in a lake
Mute swans. Credit: Paul Rose

“However, there was no apparent trade-off between some behaviours, such as aggression and foraging, and aggression and maintenance,” says Rose.

“We get lots of questions from our visitors about the aggressiveness of swans,” says co-author Dr Kevin Wood, from the Wildfowl & Wetlands Trust. “This new study helps us to understand how swans’ behaviour changes when they engage in their disputes.”

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Lake filled with swans and other birds
Mute and whooper swans along with other species at Caerlaverock, where the study was done. Credit: Paul Rose

Rose says that providing more foraging ground for swans would reduce their desire to squabble with each other, meaning they could rest more.

This is particularly important for migratory whooper swans, which need to rest so they can store up enough fat to migrate to their breeding grounds in Iceland.

“This can help to ensure that migratory species don’t ‘push out’ non-migratory species when they mix in the same wintering locations,” says Rose.

“Our study also demonstrates how remotely collected data can be used to investigate fundamental questions in behavioural research.”

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