UKBirds

Jackdaw

Corvus monedula

The Western Jackdaw, sometimes known as the Eurasian Jackdaw, European Jackdaw or simply Jackdaw, is a passerine bird in the crow family. Found across Europe, western Asia and North Africa, it is mostly resident, although northern and eastern populations migrate south in winter. Four subspecies are recognised, which mainly differ in the colouration of the plumage on the head and nape. Linnaeus first described it formally, giving it the name Corvus monedula. Later analysis of its DNA shows that, with its closest relative the Daurian Jackdaw, it is an early offshoot from the genus Corvus, and possibly distinct enough to warrant reclassification in a separate genus, Coloeus. The common name derives from the word "jack", meaning "small", and "daw", the native English name for the bird.

Measuring 34-39 centimetres (13-15 in) in length, the Jackdaw is a black-plumaged bird with a grey nape and distinctive pale-grey irises. 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. It is an omnivorous and opportunistic feeder, eating a wide variety of plant material and invertebrates, as well as food waste from urban areas. Jackdaws are monogamous and build simple nests of sticks in cavities in trees, cliffs, or buildings. About five pale blue or blue-green eggs with brown speckles are laid and incubated by the female. The young then fledge in four to five weeks.

Measuring 34-39 centimetres (13-15 in) in length, the Western Jackdaw is the second smallest member of the genus Corvus. Most of the plumage is a shiny black, with a purple (in subspecies monedula and spermologus) or blue (in subspecies cirtensis and soemmerringii) 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, which makes up about 75% of the length of the head. There are rictal bristles covering around 40% of the upper mandible and 25% of the lower mandible. 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. Jackdaws undergo a complete moult from June to September in the western parts of their range, and a month later in the east. The purplish sheen of the cap is most prominent just after moulting.

Immature birds have duller and less demarcated plumage. The head is a sooty black, sometimes with a faint greenish sheen and brown feather bases visible; the upperparts and side of neck are dark grey and the underparts greyish or sooty black. The tail has narrower feathers and a greenish sheen.

There is very little geographic variation in size. The main differences are the presence or absence of a whitish partial collar at the base of the nape, the variations in the shade of the nape and the tone of the underparts. Populations in central Asia have slightly larger wings and western populations have a slightly heavier bill. Body colour becomes darker further north, in mountain regions and humid climates, and paler elsewhere. However, individual variation, particularly in juveniles and also during the months before premoult (after April), can often be greater than geographic differences.

A skilled flyer, the Western Jackdaw can manoeuvre tightly as well as tumble and glide. It has characteristic jerky wing beats when flying, though these are not evident when birds are migrating. Wind tunnel experiments show the preferred gliding speed to be between 6 and 11 metres per second, and that the wingspan decreases as the Jackdaw flies faster. On the ground, Western Jackdaws have an upright posture and strut briskly, their short legs giving them a rapid gait. They feed with their heads held down or horizontally.

Within its range, the Western Jackdaw is unmistakable; its short bill and grey nape are distinguishing features. From a distance, it can be confused with a Rook (Corvus frugilegus), or when in flight, with a pigeon or chough. Flying Western Jackdaws are distinguishable from other corvids by their smaller size, faster and deeper wingbeats and proportionately narrower and less fingered wing tips. They also have shorter, thicker necks, much shorter bills and frequently fly in tighter flocks. They can be distinguished from choughs by their uniformly grey underwings and their black beaks and legs. The Western Jackdaw is very similar in morphology, behaviour, and calls to the Daurian Jackdaw, with which its range overlaps in western Asia. Adults are readily distinguished, since the Daurian has a pied plumage, but immature birds are much more similar, both species having dark plumage and dark eyes. The Daurian tends to be darker, with a less contrasting nape than the Western.

Western Jackdaws are voluble birds. The main call, frequently given in flight, 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, has been transcribed 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. Jackdaws also have a hoarse, drawn-out alarm call, arrrrr or kaaaarr, used when warning of predators or when mobbing them. Nestling Western Jackdaws begin making a soft cheep at about a week of age. As they grow, their voice becomes louder until their call is a penetrating screech around day 18. After this, the voice deepens and softens. From day 25, the young cease calling and become silent if they hear an unfamiliar noise.