In this edition of Field Talk, we catch up with Ethan Temeles, a biologist at Amherst College, who tells us a tale of competition among the sexes in Caribbean hummingbirds – competition so severe that it drives their evolution. The short, straight bills of male purple-throated caribs and the long, curved bills of female caribs correspond to the shape of heliconia flowers on which they feed. The story got more complicated, though, when Dr. Temeles and his students discovered that despite their curved bills, females prefer straight flowers to curved ones. Join us as Dr. Temeles explains how this species’ sexual dimorphism evolved, and read more in his paper in the May issue of Ecology.