page_title: Western jackdaw
section_title: Breeding
hierarchical_section_title: Western jackdaw / Behaviour / Breeding
caption_attribution_description: Deutsch: Dohle Corvus monedula, Ei, Coll. Museum Wiesbaden, Fundort: Neusiedler See, Oesterreich, 19.04.1973, leg. W. Abelmann English: Western jackdaw Corvus monedula, egg, Coll. Museum Wiesbaden, Origin: Lake Neusiedl, Austria, 19.04.1973, leg. W. Abelmann
context_page_description: The western jackdaw, also known as the Eurasian jackdaw, the European jackdaw, or simply the 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 the winter. Four subspecies are recognised, which differ mainly in the colouration of the plumage on the head and nape. Linnaeus first described it formally, giving it the name Corvus monedula. The common name derives from the word jack, denoting "small", and daw, a less common synonym for "jackdaw", and the native English name for the bird.
  Measuring 34–39 centimetres in length, the western 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. Like its relatives, jackdaws are intelligent birds, and have been observed using tools. An omnivorous and opportunistic feeder, it eats a wide variety of plant material and invertebrates, as well as food waste from urban areas.
context_section_description: Western jackdaws become sexually mature in their second year. Genetic analysis of pairs and offspring shows no evidence of extra-pair copulation and there is little evidence for couple separation even after multiple instances of reproductive failure. Some pairs do separate in the first few months, but almost all pairings of over six months' duration are lifelong, ending only when a partner dies. Widowed or separated birds fare badly, often being ousted from nests or territories and unable to rear broods alone.
  Western jackdaws 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, the common feature being a sheltered site for the nest. The availability of suitable sites influences their presence in a locale. They may also use church steeples for nesting, a fact reported in verse by 18th century English poet William Cowper:
  A great frequenter of the church,
  
  Where, bishoplike, he finds a perch,
  
  And dormitory too.
  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. This behaviour has led to the blocking of chimneys and even resulted in nests crashing down into fireplaces, sometimes with birds still on them.
  In his The Natural History of Selborne, Gilbert White notes that western jackdaws used to nest in crevices beneath the lintels of Stonehenge, and describes an example of the bird using a rabbit burrow for nesting. The species has been recorded outcompeting the tawny owl (Strix aluco) for nest sites in the Netherlands. They can take over old nest sites of the black woodpecker (Dryocopus martius) and stock dove (Columba oenas). 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.
  Nests are lined with hair, wool, dead grass and many other materials. The eggs are a lighter colour than those of other corvids, being smooth, a glossy pale blue or blue-green with darker speckles ranging from dark brown to olive or grey-violet. Egg size and weight varies slightly between subspecies; those of subspecies monedula average 35.0 by 24.7 millimetres (1.38 in × 0.97 in) and 11.1 g (0.39 oz) in weight, those of subspecies soemmerringii 34.8 by 25.0 millimetres (1.37 in × 0.98 in) in size and 11.3 g (0.40 oz) in weight, and those of subspecies spermologus 35.0 by 25.2 millimetres (1.38 in × 0.99 in) in size and 11.5 g (0.41 oz) in weight. Clutches usually contain 4 or 5 eggs, although a Slovakian study found clutch sizes ranging from 2 to 9 eggs. The eggs are incubated by the female for 17–18 days until hatching as naked altricial chicks, which are completely dependent on the adults for food. They fledge after 28–35 days, and the parents continue to feed them for another four weeks or so.
  Western jackdaws hatch asynchronously and incubation begins before clutch completion, which often leads to the death of the last-hatched young. If the supply of food is low, parental investment in the brood is kept to a minimum as little energy is wasted on feeding a chick that is unlikely to survive. Replacement clutches are very rarely laid in the event of clutch failure.
  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. Nest robbers include the common raven in Spain, tawny owl, and least weasel (Mustela nivalis) in England, and brown rat (Rattus norvegicus) in Finland. The European pine marten (Martes martes) raids isolated nests in Sweden but is less successful when nests are part of a colony.
caption: Eggs, Collection Museum Wiesbaden
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