The jackdaw is a highly sociable species outside of the breeding season, occurring in flocks that can contain hundreds of birds (6). Within flocks there is a strict hierarchy, with a head bird (6). Occasionally the flock makes 'mercy killings', in which a sick or injured bird is mobbed until it is killed (6).
The jackdaw typically feeds on the ground, taking insects and insect larvae, young birds, fruit and acorns (6). This is a playful species, performing aerobatics such as turning over in strong winds and diving; occasionally entire flocks may perform such displays at the same time (6).
Males and females pair up in their first year of life, but they do not begin to breed for another year; the pair remains closely tied for life (6). Nests are usually constructed in some type of crevice, the pair drops sticks into the crevice until some become lodged; the nest is then built on this platform (6). This behaviour has often led to chimneys being blocked and even nests, with the birds present, crashing down into fireplaces (7). The pair defend their nest vigorously against intruding jackdaws (6). Four to six greenish-blue eggs are laid and incubated for up to 17 days by the female (6). Both parents feed the chicks for around 30 days (6).