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Birds will mock-up the scene of an attack to stop rivals from stealing their nest.
Researchers found that cavity-nesting birds were much slower and less likely to enter holes with white feathers in, suggesting the animals are afraid a predator is already in residence.
Like the best murder mystery, some birds may intentionally fake their own death to protect their nests. By incorporating white feathers into their nests, resident birds may be deterring rivals by suggesting that a predator is lurking inside.
A team of international researchers found that three different species of birds which typically nest in holes or cavities hesitated to enter unfamiliar nest boxes when white feathers were inside. The scientists suggest that the detached feathers make the animals wary that a bird has been attacked by a predator.
In the wild, this helps birds prevent their nests from being stolen by a rival, with individuals incorporating white feathers found in the environment into their nests.
Douglas Russell, Senior Curator of birds at the Museum who looks after the nest collections, says, 'It's always fascinating to see new hypotheses on what might lead to decision-making in birds. The fear of feathers hypothesis is certainly a concept that should be further investigated.'
The research, conducted by Norwegian and Canadian scientists, was published in Royal Society Open Science.
But underneath the tough outer feathers, there is a layer of soft, fluffy feathers known as down. These feathers play an important role in keeping the bird warm and are normally only exposed on the underside of the animal.
As they aren't for show, down feathers often have muted tones such as white and grey. While they can fall out naturally, these feathers lying on the ground can suggest a dead bird has been plucked by a predator.
Smaller mammals and birds of prey frequently use cavities in trees and other structures to eat their prey, but some birds also make use of the same holes to build nests. Researchers wanted to see if the presence of feathers at these sites would warn away a broody bird or if they would get on with building a nest.
To test this, the scientists looked at three species which nest in cavities: pied flycatchers, blue tits and tree swallows. They gave the animals a choice of nest boxes, in which they changed the presence, number and colour of artificial feathers, as well as putting in paper labels to see if colour alone affected their behaviour.
The researchers found that all three species were much more hesitant at entering a nest box when white feathers were inside. When given the choice between a box with white feathers and one with black feathers, or no feathers, blue tits and tree swallows spent almost an hour longer before entering the boxes when white feathers were present
Even pied flycatchers, which prefer to nest in abandoned or even still occupied tit nests, waited around half an hour more when given the choice between a feathered nest and a non-feathered one. In almost a third of all trials, birds would never enter a nest box with white feathers in.
The effect was specific to feathers, with birds entering nests with white paper labels more quickly than those with white feathers. Even once the birds had already entered the box they were still suspicious, with blue tits shown to be more hesitant to re-enter even after they had found the box to be safe.
Even though many birds eventually entered the boxes regardless of feathers, the researchers suggest that the feathers cause the incoming animals to hesitate just long enough that the nest's owner is likely to return. White feathers are more visible from the outside than black ones, increasing the effect.
In the case of pied flycatchers stealing tit nests, females can begin building their nest in just a few hours of taking over. Extra hesitancy ensures there is a greater chance the tits inhabiting the nest will return and force them to leave.
The feathers also have added benefits, including strengthening the nest as well as keeping developing eggs and newborn chicks warm. There is also evidence that other materials, such as snake skins, are also used by birds when building their nests to induce fear.
The researchers now hope to find out whether feathers in the nest discourage potential predators, as well as birds like the cuckoo which lay their eggs in other nests.