24-3-2017 RANCHO NATURALISTA, COSTA RICA - MONTEZUMA OROPENDOLA (Psarocolius montezuma) COURTESY MRS VALERIE FISHER

The Montezuma Oropendola (Psarocolius montezuma ) is a New World tropical icterid bird. It is a resident breeder in the Caribbean coastal lowlands from southeastern Mexico to central Panama, but is absent from El Salvador and southern Guatemala. It also occurs on the Pacific slope of Nicaragua and Honduras and northwestern and southwestern Costa Rica. It is among the oropendola species sometimes separated in the genus Gymnostinops. The English and scientific names of this species commemorate the Aztec emperor Moctezuma II.

The sexes are very different in size; the male is 50 cm (20 in) long and weighs 520 g (18 oz); the smaller female is 38 cm (15 in) long and weighs 230 g (8.1 oz). In total body mass, the males are 100% bigger than the females, which is a 2:1 body-to-mass ratio and makes the Montezuma oropendola one of the most sexually-dimorphic birds in the world. Webster et al. says that the size difference in males and females is probably directly related to differences in foraging habits. The females often forage on thin branches, eating insects out of curled up leaves, while the males often perch on thick branches and forage in epiphytes and bromeliads.