It is gregarious and vocal, living in small groups with a complex social structure in farmland, open woodland, on coastal cliffs, and in urban settings.

Other dialectal or obsolete names include caddesse, cawdaw, caddy, chauk, college-bird, jackerdaw, jacko, ka-wattie, chimney-sweep bird (from their nesting propensities), and sea-crow (from the frequency with which they are found on coasts).

[19] This led Pamela Rasmussen to reinstate the genus name Coloeus, created by Johann Kaup in 1829,[20] in her Birds of South Asia (2005),[21] a treatment also used in a 1982 systematic list in German by Hans Edmund Wolters.

[37] Wind tunnel experiments show that the preferred gliding speed is between 6 and 11 metres (20 and 36 ft) per second and that the wingspan decreases as the bird flies faster.

[37] Flying western jackdaws are distinguishable from other corvids by their smaller size, faster and deeper wingbeats and proportionately narrower and less fingered wing tips.

[44] The western jackdaw is found from Northwest Africa through all of Europe, except for the subarctic north, and eastwards through central Asia to the eastern Himalayas and Lake Baikal.

[37] Along with other corvids such as the rook, common raven (Corvus corax), and hooded crow (C. cornix), some western jackdaws spend the winter in urban parks; populations measured in three urban parks in Warsaw show increases from October to December, possibly due to western jackdaws migrating there from areas further north.

[56] Flocks increase in size in autumn and birds congregate at dusk for communal roosting,[13] with up to several thousand individuals gathering at one site.

[58] Western jackdaws sometimes mob and drive off larger birds such as European magpies, common ravens, or Egyptian vultures (Neophron percnopterus); one gives an alarm call which alerts its conspecifics to gather and attack as a group.

[59] In his book King Solomon's Ring, Konrad Lorenz described and analysed the complex social interactions in a western jackdaw flock that lived around his house in Altenberg, Austria.

A mated pair usually constructs a nest by improving a crevice by dropping sticks into it; it is then built on top of the platform formed.

[62] Breeding colonies may also edge out those of the red-billed chough, but in turn be ousted by larger corvids such as the carrion crow, rook or magpie.

[68] The eggs are a lighter colour than those of other corvids,[69] being smooth, a glossy pale blue or blue-green with darker speckles ranging from dark brown to olive or grey-violet.

[70] The great spotted cuckoo (Clamator glandarius) has been recorded as a brood parasite of the western jackdaw, depositing its eggs in their nests in Spain and Israel.

[73][74] Nest robbers include the common raven in Spain, tawny owl, and least weasel (Mustela nivalis) in England, and brown rat (Rattus norvegicus) in Finland.

[76] Jackdaws will ride on the backs of sheep and other mammals, seeking ticks as well as actively gathering wool or hair for nests, and will catch flying ants in flight.

[77] The western jackdaw tends to feed on small invertebrates up to 18 millimetres (0.71 in) in length that are found above ground, including various species of beetle (particularly cockchafers of the genus Melolontha,[78] and weevil larvae and pupae.

Vegetable items consumed include farm grains (barley, wheat and oats), weed seeds, elderberries, acorns, and various cultivated fruits.

[76] Examination of the gizzards of western jackdaws shot in Cyprus in spring and summer revealed a diet of cereals (predominantly wheat) and insects (notably cicadas and beetles).

[40] A study in southern Spain examining western jackdaw pellets found that they contained significant amounts of silicaceous and calcareous grit to aid digestion of vegetable food and supply dietary calcium.

[78] A field study of a large city dump on the outskirts of León in northwestern Spain showed that western jackdaws forage there in the early morning and at dusk, and engage in some degree of kleptoparasitism.

[86] Western jackdaws practice active food sharing – where the initiative for the transfer lies with the donor – with a number of individuals, regardless of sex or kinship.

The function of this behaviour is not fully understood, though it has been found to be detached from nutrition and compatible with hypotheses of mutualism, reciprocity and harassment avoidance.

[88] Western jackdaws have learned to peck open the foil caps of milk bottles left on the doorsteps after delivery by the milkman.

This activity was linked to cases of Campylobacter gastroenteritis in Gateshead in northeast England[89] and led the Department of Health to suggest that milk from bottles which had been pecked open should be discarded.

[93] After a series of poor harvests in the early 1500s, Henry VIII introduced a Vermin Act in 1532 "ordeyned to dystroye Choughes (i.e. jackdaws), Crowes and Rokes" to protect grain crops from their predations.

[94] In a 2003 dissertation on public opinion of corvids, Antonia Hereth notes that the German naturalist Alfred Brehm considered the western jackdaw to be a lovable bird, and did not describe any negative impacts of this species on agriculture.

[80] An ancient Greek and Roman adage runs "The swans will sing when the jackdaws are silent", meaning that educated or wise people will speak only after the foolish have become quiet.

[99] The mythical Princess Arne Sithonis was bribed with gold by King Minos of Crete, and was punished by the gods for her greed by being transformed into an equally avaricious jackdaw, who still seeks shiny things.

The 12th-century historian William of Malmesbury records the story of a woman who, upon hearing a jackdaw chattering "more loudly than usual," grew pale and became fearful of suffering a "dreadful calamity", and that "while yet speaking, the messenger of her misfortunes arrived".