Breeding

Montezuma Oropendolas nest colonially. Nests are built in tall, isolated trees, with disjunct canopies located in cleared areas (Webster 1994a); and tree heights range 12-30 meters (Fraga 1989). The nest is a long pouch attached to a terminal twig or branch, constructed from multiple fibrous sources and lined with leaves for cushion and/or insulation (Webster 1994a). Nests are constructed solely be the female. A sample of fallen nests (n = 28) measured 111.3 ± 26.5 cm in length, 68.3 ± 5.7 cm in circumference, and 414.4 ± 101.4 g in dry weight (Webster 1994a.
Webster (1994a) also observed that females incubated the eggs and fed the newly hatched birds with no assistance from males. Incubation time lasts 15.5 ± 1.9 days (n = 14 nests); the nestling period lasts from 29-42 days.
Clutch size is believed to be 2 eggs (Skutch 1954), but nests rarely fledge more than one bird (Webster 1994a). The eggs are white or buffy (Stiles and Skutch 1989).
Mean egg dimensions are: length 36.80 ± 2.41 mm, breadth 26.24 ± 1.14 mm, volume 12.58 ml, thickness of 0.187 mm (Spaw and Rohwer 1987).

Montezuma Oropendola is vulnerable to brood parasitism by Giant Cowbird (Molothrus oryzivorus) (Crandall 1914, Skutch 1954, Webster 1994c). Oropendolas attempt to defend against cowbirds that approach active oropendola nests (Skutch 1954, Webster 1994c), and at least occasionally oropendolas remove cowbird eggs from their nests (Skutch 1954).