Eurasian jackdaw

Description

The eurasian jackdaw is a medium-sized corvid with a body length of 33-39 cm. It appears stocky - especially in comparison with most ravens and crows - and has a stout, strong beak and relatively short legs. The jackdaw's tail is of medium length and slightly rounded in comparison to the genus, its wings are round, weakly digitated and fall slightly behind the tail when attached. Male jackdaws grow larger on average than females, although there is overlap in the dimensional ranges: Males reach a wing length of 208-255 mm and a tail length of 122-138 mm. Their beak grows to 20.6-21.5 mm from the nostrils to the tip, and the male tarsometatarsus 42.3-49.0 mm. The male weight is 174-300 g. With 205-250 mm wing length, 115-134 mm tail length, a 19.8-23.2 mm long bill and 41.2-46.5 mm length of the tarsometatarsus, and a weight of 175-282 g, females achieve only slightly smaller maximum measurements, but significantly smaller mean values.

The sexes are very similarly coloured, differing at most in a slightly lighter colouration of male birds at certain times of the year. The nasal bristles, forehead, crown, eye area, cheeks and chin down to the throat are black in adult jackdaws. The black head plate has a metallic blue or violet shimmer. The back of the crown, the back of the head, the nape of the neck and the ear coverts contrast with the black crown due to their light to slate grey coloration, but merge into black in the cheek, throat and nape area. On the sides of the neck and in the nape of the neck, some individuals develop a sometimes more, sometimes less distinct, silver-grey band, which becomes broader towards the breast and separates the plumage of the head from the body plumage. The eurasian jackdaw's back, like its wings and tail, is black-grey to black.[2] The wing feathers have a faint greenish or bluish sheen. The underparts - breast, flanks, belly and abdomen - are slate grey and darker than the back of the head. From moult to moult, especially the grey areas of the plumage fade. In black feathers, usually only the edges fade, resulting in a scaly pattern on the back. The nasal bristles turn rusty brown with time. Old birds have a whitish-blue iris, which contrasts strikingly with the black facial plumage. Their beak is black, as are their legs.
Juveniles differ from adults in colour only in a few details. Their plumage colours are duller and have much less sheen than adults. The black parts of the adult plumage appear more brownish or greyish, and the colour separation of the head plate from the back of the head is less distinct. The most obvious difference is the eye colour: after the juvenile moult, the iris colour of the birds changes from light blue to dark brown. Only after about one year does it become lighter again on the outside, and from the third year of life it is completely white-blue again.

The availability of potential breeding sites and suitable areas for foraging influence the habitat selection of the eurasian jackdaw. As a predominantly cavity-nesting bird, it is strongly dependent on old wood stands with woodpecker cavities, on rock holes or on buildings with sufficient niches in its habitat, at least during the breeding season. Quarries, rocky coasts, settlements with old buildings, medieval churches as well as parks and groves with large, old trees are therefore frequently used breeding habitats by the jackdaw. They also serve as roosting sites outside the breeding season. Forests are colonised only at the edges (maximum 2 km from the forest edge).

The species needs relatively wide open areas to forage on the ground. These areas must have low vegetation (maximum 15-20 cm) so that the eurasian jackdaw can move around on them, so parkland and pastureland are preferred. Because they should also be rich in insects, the bird likes to use dry grasslands and extensively cultivated areas. In the course of the year, the eurasian jackdaw uses very different areas - pastures, steppes, stubble fields, floodplains - for foraging.

The eurasian jackdaw is relatively weather and temperature tolerant, but avoids extremes of heat and cold. It is more likely to be found in lowlands and valleys than in mountainous areas. Below 500 m it is usually widespread, between 500 and 1000 m it is often found only in local aggregations. In some exceptional cases, breeding habitats extend beyond 1000 m, for example in the Alps, in the Atlas or in Kashmir up to about 2000 m. Outside the breeding season, it can also be found at altitudes of up to 3500 m.

The text is a translation of an excerpt from Wikipedia (https://de.wikipedia.org/wiki/Dohle). On wikipedia the text is available under a „Creative Commons Attribution/Share Alike“ licence. Status: 14 December 2021