Brown Jays live and travel in large groups (mean 10 individuals, range 5-24 individuals), which is believed to increase reproductive success (Williams and Hale 2006, dos Anjos 2009). Occasionally, birds leave their home flocks and spend hours to several days with another flock, presumably in an attempt to disperse or form breeding pairs (Lawton and Lawton 1985).
Typically forage in groups ranging from 5-24 individuals (dos Anjos 2009). Foraging generally begins half an hour before sunrise after "rallying" behavior, which consists of bursts of vocalizations followed by rapid flight through the canopy (Morrison and Slack 1977). By mid-morning, adults and juveniles typically separate resulting in small group sizes (Morrison and Slack 1977). Foraging occurs more frequently in lower vegetation strata in the later parts of the day (dos Anjos 2009). Brown Jays only spend about 6.5% of their daily time budget on the ground and only to capture food (Morrison and Slack 1977). They have been observed following army ants (Eciton burchelli) in mixed flocks, consuming arthropods and frogs (Haemig 1989). Also forages with Montezuma Oropendolas (Psarocolius montezuma) in banana plantations for banana nectar (Skutch 1960). Adults are generally silent while foraging whereas juveniles may call while foraging in the canopy (dos Anjos 2009).
Aggressive behaviors, including aerial chasing and harsh calling, are often observed in encounters between territorial flocks. In 31% of encounters aggression led to fights between individuals, which included pecking and foot-grappling (dos Anjos 2009). Observations of such territorial aggression have lasted 10 minutes to 3 hours (dos Anjos 2009). However, in 27% of encounters between flocks, non-aggressive behavior was observed (dos Anjos 2009).
Following population expansion in Monteverde, Costa Rica, aggressive interactions between flocks increased substantially, potentially due to increased reproductive competition (Williams et al. 1994). Aggressive interactions were generally observed at or near nest sites and were more common during the early breeding season. Females engaged in 85% of aggressive interactions during nest building and incubation stages. Aggressive interactions included chasing, stealing food and twigs, and attempting to force individuals out of nests (Williams et al. 1994).
Home range sizes vary from 10-20 hectares (Lawton and Guindon 1981).
Mating system and sex ratios
Mating system varies, especially in the Monteverde, Costa Rica population (Lawton and Lawton 1985). Groups generally consist of a nuclear breeding pair and helpers, however in some groups multiple females contribute to the clutch (Lawton and Lawton 1985). In Monteverde, average clutch size is double the average outside of Monteverde, which suggests that multiple female clutches are fairly common (Lawton and Lawton 1985). Males have been observed in close association with two females and multiple males in close association with one female (Williams et al. 1994).
Courtship feeding by males often precedes copulation (Lawton and Lawton 1985). Females perched in a tree will utter a whine call, lift her tail, spread her wings, and look at the potential mate perched behind her, after which the male will approach her with food. The female retreats to another branch and is followed by the male. This repeats until either the birds fly off or the male copulates with the female (Lawton and Lawton 1985).
Extra-pair copulations appear to be fairly common (Lawton and Lawton 1985). Males in a living group and non-group member males are often genetic fathers of offspring, raising the possibility of extra-pair copulations (Williams 2004).
Social and interspecific behavior
Brown Jays live and travel in large groups (mean 10 individuals, range 5-24 individuals). Also sometimes forages with Montezuma Oropendolas (Psarocolius montezuma) (Skutch 1960).
Kinds of predation
Brown Jays are likely most vulnerable to diurnal predators such as raptor, monkeys, and cats. Nest placement likely reduces risk of nocturnal predators that hunt forest canopy such as opposums, weasels, margays, ocelots, and some snakes (Lawton and Lawton 1980). Emerald Toucanet (Aulacorhynchus prasinus), Broad-winged Hawk (Buteo platypterus), Swallow-tailed Kite (Elanoides forticatus), Collared Forest-Falcon (Micrastur semitorquatus), White-faced Capuchins (Cebus capucinus), coatimundis (Nasua nasua), Tayras (Eira barbara), Variegated Squirrels (Sciurus variegatoides), Common Black Hawks (Buteogallus anthracinus), Red-bellied Squirrels (Rubrisciurus rubriventer), and various snakes are known to prey on Brown Jays (Lawton and Lawton 1980, Williams and Hale 2006).
Response to predation
Predation may be the largest threat to nesting success. It is suggested that Brown Jays mostly build nests in isolated trees in order to reduce predation risk (Lawton and Lawton 1980). Brown Jays are very aggressive and have been observed mobbing and driving off potential predators (Williams and Hale 2006). In Monteverde, Costa Rica, they have been observed fending off Broad-winged Hawks, Common Black Hawks (Buteogallus anthracinus), Red-bellied Squirrels, White-faced Capuchins, and domestic cats (Lawton and Lawton 1980).