Crossbills: The bird that gets redder feathers, the more it exercises

A Scottish crossbill

Do you ever go a bit red after exercising? Well, it turns out the same might be true for a certain type of bird!

New research shows that male crossbills grow redder feathers when they exercise harder.

Crossbills are a type of finch and have a beak - or bill - which is crossed over at the tip, giving them their name. This crossed bill is used to extract seeds from conifer cones.

Scientists from the Spanish National Research Council in Madrid have found a link between how hard a male crossbill has to work to fly, and how red his feathers are.

The bright colouring of some birds comes from things they eat in their diet - they take in special pigments from their food and use these to make the vibrant colours seen in their feathers.

For example, flamingos are born with grey feathers but the more they eat certain foods, the pinker their feathers get!

In an experiment to test this, between October 2019 and February 2020, scientists captured 295 male crossbills in central Spain, taking measurements of their colour, size and weight.

The researchers clipped some wing feathers from about half the crossbills to make flying more physically challenging.

When the team caught and checked the birds later on, they found that the birds with clipped wings had redder feathers.

This led the team to conclude that red feathers were partially a result of exercise and not just because of a bird's diet and foraging skills.

"We might conventionally assume that birds with impaired flight are 'lower quality', but here they are growing redder feathers," says Rebecca Koch at the University of Tulsa, Oklahoma, adding that study's approach is "breathing fresh life" into work on feather pigments.