BioEd Online

It takes brains to make it through the winter, at least if you're a bird. A new survey suggests that bird species that have evolved to fly south for the coldest months tend to be those that weren't smart enough to survive if they stayed put.

The study shows that migratory birds, which leave temperate regions in search of warmer climes when temperatures start to dip, have smaller brains than those who stay behind. Non-migrating species also show more creativity when it comes to finding a meal in the frugal winter months.

Daniel Sol of the Independent University of Barcelona in Spain and his colleagues used previous observations of 134 bird species in Europe, Scandinavia and western Russia. They collected data on brain size, and also counted the number of times researchers had spotted the birds adopting a novel feeding technique.

Not-so-fussy eaters

Species that remain resident during the winter have adopted more feeding innovations, the team reports in a paper published online by Proceedings of the Royal Society¹. The blackbird, Turdus merula, for example, has been seen using twigs to clear snow away while foraging. And the bullfinch, Pyrrhula pyrrhula, has been spotted tearing flesh from chicken and duck carcasses to get a meal.

On average, non-migratory birds have been spotted using four novel feeding styles per species, compared with around three for short-distance migrants, and just over one for species that commute beyond the Sahara Desert to the south.

"Species with greater foraging flexibility seem to be able to cope with seasonal environments better, while less flexible species are forced to become migratory," say Sol and his team.

Bird brains

A similar pattern was seen in brain size, with the resident species tending to have more upstairs than short-distance migrants, who in turn had larger brains than the long-distance fliers.

Brain tissue requires a lot of energy, the researchers say. So migratory birds, which expend a large chunk of their energy commuting, may benefit from having smaller brains to maintain. But, the team argues, small brains probably forced the birds to adopt a migratory lifestyle in the first place, because they were not smart enough to cope with winter.

Their lack of inventiveness may mean that migratory species will have more trouble adapting to future changes in environmental conditions, Sol and his colleagues add. With climate change and human intervention changing the landscape, these birds may be at greater risk of extinction than those that stay put.