Swans more aggressive to own kind than to other birds, study suggests

Swans display more aggression to fellow swans than to other birds, new research shows.

Three species of swan – mute, whooper and Bewick’s – were all most frequently aggressive to their own kind.

The findings suggest that similar individuals are the greatest competition for food and other resources such as shelter, which can lead to conflict.

Mute Swans fighting at Slimbridge (Wildfowl and Wetlands Trust/PA)
Mute Swans fighting at Slimbridge (Wildfowl and Wetlands Trust/PA)

The research, by the Wildfowl and Wetlands Trust (WWT) and the University of Exeter, was undertaken to better understand how swan behaviour affects other waterbirds over winter.

Dr Kevin Wood, from the WWT, said: “We know that swans have a reputation for aggressiveness but some of us suspected that in reality a lot of the aggression was directed towards other swans rather than smaller birds such as ducks or geese.

“To test that idea, we recruited some great students who used the webcams at Slimbridge and Caerlaverock to collect behavioural data on aggressive interactions between the various waterbirds at those sites over the past two winters.

“Our suspicions were right.

“In fact, almost all of the waterbird species in our study were most aggressive to their own species, which makes ecological sense as the individuals that are most similar to you are your greatest competition for food and other resources.

“It’s valuable to finally have the data to show that, and it’s another rung on the ladder of better-informed judgment on swans.”

The study was carried out by monitoring live-stream webcams on reserves at WWT Slimbridge Wetland Centre in Gloucestershire and WWT Caerlaverock Wetland Centre in Dumfries over the past two years.

Whooper swans calling at the Welney Wetlands Centre (Wildfowl and Wetlands Trust/PA)
Whooper swans calling at the Welney Wetlands Centre (Wildfowl and Wetlands Trust/PA)

It is one of the first studies to rely completely on remotely collected data and could be one of the solutions to continuing research with restrictions in place during the Covid-19 pandemic.

Dr Paul Rose, from the University of Exeter, said: “This is a great example of how undergraduate projects can really help wild conservation action by allowing students to practise key research techniques but at the same time collecting data that is valuable to field scientists.”

Across whooper, Bewick’s and mute swans, infighting between the same species accounted for up to 80% of negative interactions.

Bewick’s swans were more likely to behave aggressively with one another, which could reflect their extreme lifestyles that involve a 4,350-mile (7,000km) migration across a continent twice a year.

The number of Bewick’s swans wintering in the UK declined by more than 50% between 1995 and 2015, with numbers continuing to fall.

The next step is to study other waterbirds to see how their behaviour alters depending on the presence and number of swans.

– The paper, Aggressive Behavioural Interactions Between Swans (Cygnus spp) And Other Waterbirds During Winter: A Webcam-based Study, is published in the journal Avian Research.