The Western jackdaw is a passerine bird that belongs to the crow family. Most of its plumage is a shiny black, with a purple or blue sheen on the crown, forehead, and secondaries, and a green-blue sheen on the throat, primaries, and tail. The cheeks, nape, and neck are light grey to greyish-silver, and the underparts are slate-grey. The legs are black, as is the short stout bill. The irises of adults are greyish or silvery-white while those of juveniles are light blue, becoming brownish before whitening at around one year of age. The sexes look alike, though the head and neck plumage of male birds fades more with age and wear, particularly just before moulting.
Western jackdaws are 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. To the east, they occur throughout Turkey, the Caucasus, Iran, Iraq, Afghanistan, Pakistan, and northwestern India. These birds are mostly resident, although northern and eastern populations migrate south in the winter. Western jackdaws live in wooded steppes, pastures, cultivated land, coastal cliffs, and towns. Preferred habitats include a mix of large trees, buildings, and open ground.
Western jackdaws are highly gregarious and are generally seen in flocks of varying sizes. In autumn flocks usually increase in size and birds congregate at dusk for communal roosting, with up to several thousand individuals gathering at one site. Jackdaws are active during the day and forage mostly on the ground in open areas and sometimes in trees. While feeding they use various methods such as jumping, pecking, clod-turning, and scattering, probing the soil, and occasionally, digging. Jackdaws spend a lot of time exploring and turning over objects with their bill; they have a straight and not too downturned bill and increased binocular vision which are advantageous for this foraging strategy. Western jackdaws are very vocal birds. Their main call is a metallic and squeaky 'chyak-chyak' or 'kak-kak'. This is a contact or greeting call. A feeding call made by adults to call young, or males when offering food to their mates, sounds as 'kiaw' or 'kyow'. Females in return give a more drawn out version when begging for food from males, written as 'kyaay', 'tchaayk' or 'giaaaa'. Perched birds often chatter together, and before settling for the night, large roosting flocks make a cackling noise. Western jackdaws also have a hoarse, drawn-out alarm call, 'arrrrr' or 'kaaaarr', used when warning of predators or when mobbing them.
Western jackdaws are opportunistic and highly adaptable omnivores. They feed on beetles, spiders, snails, small rodents, bats, the eggs and chicks of birds, and carrion such as roadkill. Vegetable items consumed include farm grains (barley, wheat, and oats), weed seeds, elderberries, acorns, and various cultivated fruits.
Western jackdaws are monogamous breeders; they mate for life and pairs always stay together within flocks. They usually breed in colonies with pairs collaborating to find a nest site, which they then defend from other pairs and predators during most of the year. They nest in cavities in trees or cliffs, in ruined or occupied buildings, and in chimneys. Nest platforms can attain a great size. 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. The nest is then lined with hair, wool, dead grass, and many other materials. The female lays 4-5 eggs which are smooth, a glossy pale blue or blue-green with darker speckles ranging from dark brown to olive or grey-violet. The eggs are incubated by the female for 17-18 days until naked altricial chicks are ready to hatch. They are completely dependent on the adults for food and fledge after 28-35 days; however, the parents continue to feed them for another 4 weeks or so. The young become reproductively mature in their second year.
Western jackdaws are not threatened at present, however, they are often persecuted as pests by farmers to protect grain and fruit crops from their predation.
According to the IUCN Red List, the total population size of the Western jackdaw is 39,800,000-83,400,000 mature individuals. In Europe, the breeding population consists of 9,930,000-20,800,000 pairs, which equates to 19,900,000-41,700,000 mature individuals. Currently, this species is classified as Least Concern (LC) on the IUCN Red List and its numbers today are stable.