One of the better-studied New World jays, the white-throated magpie-jay is a large blue, black and white bird that sports jaunty black plume. It occurs primarily in tropical dry forest, and tracks this habitat through its southern limit in Guanacaste, Costa Rica, turning it over to its close relative, the black-throated magpie-jay, around Jalisco, Mexico. During the dry season, white-throated magpie-jays subsist in large part on fruits, especially those of ant-acacias. After insect activity is stimulated by rains, they focus on insects, especially the larvae of large lepidoperans.
White-throated magpie-jays are highly social and breed cooperatively. Unusually among birds, the female offspring stay in the group and help their parents raise future broods, while male offspring disperse. Therefore, groups generally consist of a dominant female, her lone social mate, and a number of retained female offspring who feed the dominant female, nestlings, and fledglings. However, dispersing males (floaters) have carte blanche to enter territories and accompany groups while foraging. Floaters may visit multiple groups in a day, and group males show little aggression to them unless the dominant female is fertile.
Such a dynamic social scene lays the groundwork for a complex mating system. Dominant females are fairly faithful to their mates, but not entirely, with paternity going to both visiting floaters and to neighboring group males. Occasionally, a helper will start a nest of her own; she is not prevented from doing so, but the group will not help her unless the nest of the dominant female fails. In addition, helpers may act as brood parasites on the nests of their own mothers, laying eggs for the group to raise. Both sexes, therefore, compete for mating opportunities; males for a chance to pair with the dominant female, and females for the dominant position in the group.
Such reproductive skew within groups seems to have lead to the evolution of one of the more astonishing vocal systems in the bird world. Male magpie-jays can individually produce upwards of 60 vocalizations (probably many more), but they do so in an unusual context. When a magpie-jay of either sex encounters a low-threat predator or even an innocuous species such as a dove or guan, they may fly slowly and directly at the threat, calling loudly. In this context males may produce a wide range of chirps, whoops, pops, yells and clicks. One possible explanation is that because male magpie-jays do not defend any resources needed by females, their best opportunity to be noticed by females is during predator encounters, when groups must pay attention to conspecific alarm calls.