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The Montezuma Oropendola (Psarocolius montezuma, sometimes known as Gymnostinops montezuma) is the largest member of the blackbird family (Icteridae). The sexes are similar in appearance, but males are considerably larger. Males average 47.5 cm long and 521 g (but some may exceed 560 g), females 39.2 cm and 246 g. The loud male song begins with low-pitched gurgles, then increases in pitch and volume, with complex harmonics, finally ending in a long note (listen to recordings under Media tab).
Montezuma Oropendolas are distributed along the Atlantic slope of central and southern Mexico and along the Caribbean slope from Belize south to southern Panama. They occur up to around 1600 m and are associated with humid tropical forest, often in clearings and edges (especially when breeding), as well as riparian forest along rivers and channels, second-growth forest, shady pastures, and plantations (banana, cacao, etc.).
The diet of Montezuma Oropendolas includes insects and other arthropods as well as small vertebrates such as frogs. Fruits are an important component of the diet, along with nectar from large flowers. Feeding is mainly high in trees, rarely lower down or on the ground. Because of the difference in size, males and females may tend to forage in different parts of a tree. Outside the breeding season, Montezuma Oropendolas often form mixed-species foraging flocks with other icterids and jays.
Montezuma Oropendolas are polygynous colonial breeders, with several to well over a hundred nests per colony constructed in one to several trees. Males in the colony form a linear dominance hierarchy, with the one or two highest ranking males siring most of the offspring in the colony. The nest, which is constructed by the female over 13 to 18 days largely from coarse plant fibers, is a purse 60 to 180 cm long, open at the top, and suspended from a branch tip. Nests are typically located over a river, channel, or road and sometimes even near buildings if the birds are unmolested. The two eggs are incubated by the female for 17 to 18 days. Nestlings are fed by the female and remain in the nest for around 35 days. Nests are often parasitized by the brood parasitic Giant Cowbird (Molothrus oryzivorus), although the host usually removes the cowbird's eggs. Males may attack nest predators and brood parasites. Reports from Costa Rica indicate that the second of the two hatchlings in a Montezuma Oropendola clutch typically survives for just a few days.
Other than some possible altitudinal movements in Costa Rica and Panama, these birds are essentially sedentary. Montezuma Oropendolas are locally common to uncommon and are found in many national parks and other protected areas. They tolerate (and may even benefit from) moderate deforestation.
(Fraga 2011 and references therein)