A population of birds in California has evolved diverse bill sizes and shapes, even within a small geographic area.

Credit: Kathryn Langin

Diversification within a species is thought to occur mainly when populations are separated by geographical barriers, such as mountains or bodies of water. To see if this happens in a single population, Kathryn Langin at Colorado State University in Fort Collins and her colleagues studied more than 500 island scrub-jays (Aphelocoma insularis; pictured), which have small ranges and live only on the 250-square-kilometre Santa Cruz Island in California.

The team found that birds living in pine forests had longer, shallower bills — presumably for prying open pine cones — than jays in oak forests, even though the two habitats were next to each other. Adaptations at this microgeographic level could be more common than once thought, even for mobile animals, the authors suggest.

Evolution http://doi.org/zt3 (2015)