A sociable species, the monk parakeet usually occurs in large, noisy flocks of around 30 to 50 individuals, with larger flocks gathering outside of the breeding season. Groups also roost together at night (5) (7).
The diet of the monk parakeet includes the seeds of various grasses, trees and other plants, as well as fruits and berries, buds, flowers and occasionally insects (2) (3) (5) (7). Cultivated fruits, seeds and vegetables are also eaten (3) (5) (7), and the monk parakeet can be a serious crop pest (2). Feeding takes place both in the trees and on the ground, and foraging flocks often mix with other bird species (5) (7). In its introduced range, the monk parakeet may obtain a lot of its food from garden bird feeders (3) (11), particularly in winter (11).
The monk parakeet breeds between October and February (2), and nesting takes place communally (2) (3) (5) (12). This species is unique among parrots in building a large stick nest rather than nesting inside cavities. The nest is built from sticks cut with the beak, often from spiny Celtis bushes, and is usually located in a tree, or sometimes on a telephone pole or pylon (2) (3) (5) (6). Sometimes only a single nest is built, but often many nests are joined together to form a large, untidy structure with many chambers, each occupied by a breeding pair (2) (3) (5) (8) (12). The inside of the nest is lined with chewed twigs (5).
Monk parakeets may roost in the nests outside of the breeding season (5) (7) (12), and other bird species also sometimes nest inside them (5). Instead of building large stick nests, the subspecies M. m. luchsi typically nests on cliffs (5).
The female monk parakeet lays clutches of up to 11 or 12 eggs, which hatch after 23 to 24 days (2) (5) (7) (13). The young parakeets leave the nest at around six to seven weeks old (2) (7). Some studies have reported quite low proportions of young surviving to fledge (13), but this species’ relatively large clutch size means it has a high reproductive rate for a parrot (2). The monk parakeet may live to around 25 years old (7).
Rather than always breeding in pairs, the monk parakeet has occasionally been observed to breed in trios. It is thought that there may be some level of cooperative breeding in this species, with young birds possibly staying with their parents to help rear subsequent broods (12).