Although it is occasionally described as a short-distance migrant, the fish crow does not truly migrate and movements are thought to be due to food availability rather than weather conditions. Similarly to other crow species, the fish crow is a highly social bird, particularly outside of the breeding season. It is known to forage in flocks of several hundred, and roosts can contain over 45,000 individuals. During the breeding season, the fish crow may congregate with conspecifics, but in much smaller groups, and roosts alongside American crows, herons and egrets. Grooming between mating pairs is frequently seen throughout the year, and the male is also known to groom large nestlings (2).
The fish crow is known to nest in solitary pairs, or in small nesting groups. It is likely that this species is monogamous, similarly to other members of the Corvidae family. Mating pairs begin building their nest between March and June and it is usually a round structure, although this is dependent on where it is placed within the tree. The nest usually takes around nine days to build and is made from freshly plucked twigs from nearby deciduous trees. Pairs are known to start building several nests at once before concentrating on one and abandoning the others. One brood of between two and six eggs is produced each breeding season and the eggs are pale bluish-green in colour and are patterned with brown markings. The female incubates the eggs while the male guards the area and will stand in the nest if the female leaves. The eggs will generally hatch after being incubated for 18 or 19 days. The young fish crows fledge the nest around five weeks after hatching, but may continue to be fed by the male and female for around a month after leaving the nest (2).
Co-operative breeding is not known among fish crows, although a third individual is often seen with a breeding pair. This third individual may help with nest-building and feeding of the brooding female and its nestlings. However, the presence of the third bird is often disruptive, and it is frequently chased away by the breeding pair. It is thought that the third individual is not a true helper and may remain close to the nest to try and mate with the incubating female (2).
The fish crow is an omnivorous species that is known to take carrion, marine invertebrates, bird and turtle eggs, young birds, insects and fruit (2) (4). The diet of an individual is heavily dependent on its location, and birds in urban areas are known to rely on human waste as one of their main food sources (2).