Montezuma Oropendola primarily forages in the canopy, searching among foliage, in epiphytes and bark crevices, and along the undersides of branches and fronds (Stiles and Skutch 1989). Specific foraging maneuvers include gleaning, poking, and prying (Stiles and Skutch 1989).
The flight of Montezuma Oropendolas is slow, with measured wingbeats, and often is at treetop level (Stiles and Skutch 1989).
Montezuma Oropendolas breed colonially, in colonies of up to 130 nests (Webster 1994a), so apparently little individual territoriality. There are no data on home range size. Fraga (1989) sampled 1109 nests (over 36 different colony sites), and found that the mean linear density was one colony every 8.7 km, with 6 colonies (341 nests) in a 19-km stretch. Nest numbers averaged 30.9 ± 35.2, and ranged 3-172 with a median of 21.5.
Montezuma Oropendola is highly polygynous.
The following summary is based largely on Webster (1994b) from a Costa Rican population. Males defend groups of sexually receptive females, and aggressively compete with each other for access to groups of females at nesting colonies. The outcome of aggressive interactions determines the rank of males. The top-ranking (alpha) male physically excludes all lower-ranking males from the colony and prevents them from approaching females. The alpha male is present at the nesting colony when the greatest number of females is present; at other times of the day, when the alpha male often was absent, lower ranking males enter the colony and defend females until the return of the alpha male. Over the course of the season, the number of males present at the colony was positively correlated with the number of sexually receptive females. Nesting within a colony is not synchronous; male competition is focused at that portion of the colony containing the highest number of nest-building females, and as a female begins laying eggs, the male's attention shifts to females that have not mated. Males also move to new colony sites whenever females move, both within and between breeding seasons. Male mating success at the focal observation colony is strongly and positively associated with dominance rank; 77% of 88 copulations observed were obtained by the alpha male. These results indicate that the Montezuma Oropendola has a female-defense mating system. This mating system is more similar to those of polygynous mammals than it is to those of most other polygynous birds (Webster 1994b).
Montezuma Oropendolas nest in colonies (multiple nests in one tree or adjacent trees). The average number of nests in these colonies is 24, but ranges up to 130 (Webster 1994a). Webster observed that 88% of nests were in distinct clusters, and that the ones that were not seemed to have some sort of pattern to them (the nest were not randomly built in places). Females breeding in colonies begin nesting 10-14 days earlier than noncolonial females (Webster 1994a). The reason for this is unknown, but it does have a direct effect on the males, increasing the likelihood that dominant males will stay close to the females and protect them (instead of guarding the territory). This ensures that the male will have better mating success the following breeding season (because the colonies do move each breeding season). As the colony size increases, the number of competing males increases (Webster 1995).
During the pre-copulatory display, the male approaches one or more females and bows to an angle of ca 45º below horizontal. Initially the male is silent, and does not ruffle the plumage. Howell (1964) described a mating display as follows: The male approached multiple females, then bowed as the females stood motionless. At this time the plumage was not shown, and no sounds were made. The male then moves to the side of one female and pecks at her outer rectrices. The male then performs a more exaggerated display, bowing, extending the neck, and pointing the bill downward while ruffling the feathers of the nape, spreading the tail and drooping the wings. Copulation follows, if the female does not leave (Howell 1964, Jaramillo and Burke 1999).
Social and interspecific behavior
Montezuma Oropendolas usually forage in small flocks, especially of females accompanied by one or more males, or, especially in the case of males solitarily (Jaramillo and Burke 1999). These flocks also may associate with other large bodied canopy species, such as White-fronted Nunbird (Monasa morphoeus), Purple-throated Fruitcrow (Querula purpurata), Black-faced Grosbeak (Caryothraustes poliogaster), Chestnut-headed Oropendola (Psarocolius wagleri), and Scarlet-rumped Cacique (Cacicus uropygialis) (Skutch 1996).
Montezuma Oropendola is reported from the diet of Ornate Hawk-Eagle (Spizaetus ornatus) (Whitacre et al. 2012), and probably is preyed upon by other large bodied raptors.