Scottish Crossbill (Loxia scotica)

Scottish Crossbill

[order] PASSERIFORMES | [family] Fringillidae | [latin] Loxia scotica | [UK] Scottish Crossbill | [FR] Bec-croise d’Ecosse | [DE] Schottischer Kreuzschnabel | [ES] Piquituerto escosses | [NL] Schotse Kruisbek

Subspecies

Monotypic species

Physical charateristics

The Scottish crossbill is a sparrow-sized member of the finch family, measuring about 16 centimetres in length, and is closely related to goldfinches and canaries. Males and females are quite different in colouration, with the male having a bright orange-red, brick-coloured plumage, while the female is a dull green-yellow, which provides her with good camouflage when she is sitting on her nest. Both males and females have dark brown wings and tails.

All crossbills are instantly recognisable by the curved mandibles which cross over when their bills are closed – they are the only type of bird which exhibits this characteristic. The mandibles cross either to the left or the right, and enable the bird to pry open the tight scales of cones and extract the seed from within them. It is the differences in bill sizes between the Scottish crossbill and its close relatives which led to it first being identified as a separate species. The common crossbill, which feeds mainly on spruce seeds contained in relatively small cones, has a slender bill, whereas the parrot crossbill has a much larger bill for opening the tougher cones of Scots pine. The bill of the Scottish crossbill is in between the others in size. The Scottish crossbill is a gregarious species, and is often seen in flocks or groups. This behaviour is thought to have arisen partly as a result of the bird’s diet, which consists almost exclusively of the seeds of Scots pine (although this has been augmented more recently by seeds of introduced exotic conifers such as European larch). As the cones of Scots pines take 2 years to ripen and cone production varies considerably from year to year, the birds have to vary their feeding grounds, depending on where the cones are abundant, and flocking may be a natural consequence of them converging on cone-laden trees.
The crossbill uses a variety of different calls and sounds, including a loud piercing cheeping call whilst in flight and a deep toop call to express a range of emotions, such as alarm or aggression.

Listen to the sound of Scottish Crossbill

[audio:http://www.aviflevoland.nl/sounddb/S/Scottish Crossbill.mp3]

Copyright remark: Most sounds derived from xeno-canto

wingspan min.: 27 cm wingspan max.: 31 cm
size min.: 16 cm size max.: 17 cm
incubation min.: 12 days incubation max.: 15 days
fledging min.: 17 days fledging max.: 15 days
broods: 1   eggs min.: 3  
      eggs max.: 4  

Range

Eurasia : Scotland

Habitat

Scottish crossbills are believed to be largely restricted to the Caledonian pine forests and old
Scots Pine plantations of the Scottish Highlands (Knox, in Gibbons et al 1993). They nest
mainly in old pine forest, including areas of bog pines, but also locally in Larches and other
predominantly coniferous woodland. Scottish Crossbills do not usually nest in dense
plantations.

Reproduction

Courtship amongst crossbills begins in late winter or early spring when the males in a flock sing loudly and in chorus, with each individual seeking to broadcast his fitness for mating. They become aggressive towards each other, and will often fight for the right to mate with a female. When a female accepts a male, she will allow him to touch her bill with his, and the male will then feed her to confirm their partnership. Mating often takes place during the process of nest-building, which is done almost exclusively by the female, although males sometimes help in the initial stages of construction. Nests are usually situated high up in pine trees, 10-15 metres above the ground, although occasionally a stunted bog pine, no more than 5 metres tall, may be used. The nest itself is made from a base of twigs, upon which grass, straw and lichen are built up, followed by a lining of moss, feathers and animal hair or fur. Nesting has been observed in all months between February and June, with March and April being the main months when eggs are laid.

The clutch size varies from 2 to 6, with 4 eggs being the most common size. The key factor which determines the size of the clutch is the availability of pine seeds, and in years of poor cone production crossbill pairs may fail to breed at all.
The female broods on the eggs for 13 to 15 days until they hatch, and during this period the male will feed her. Both birds feed the young, which leave the nest about 3 weeks after hatching. It is usually a further 10 days before the young birds’ bills become crossed, so they still depend on their parents to provide them with pine seed during this period. After this, the family group will split up, although the young may stay with one or other of their parents, and, with them, may become part of a flock.

Feeding habits

The crossbill feeds on pine seeds either by pulling a cone off a branch and then holding it with its feet while it uses its bill to extract the seeds, or it acrobatically moves around the cone, extracting the seeds without removing the cone from the branch. The location of a feeding crossbill can often be determined by the floating seed cases and occasional falling pine cones which result from its foraging. When crossbills are nesting, they will often favour particular pines near their nest which are heavily-laden with cones and will return to them repeatedly to feed.

Although pine seeds form the vast majority of their diet, crossbills occasionally feed on small shoots and buds, while in spring the females frequently feed on insects, to provide the extra protein needed to produce their eggs. Males feed on insects to a lesser extent than the females, but insects, including the larvae of the pine sawfly (Neodiprion sertifer), are sometimes brought to the young in the nest.

Conservation

Although this species has a small range, it is thought to be stable and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend appears to be stable, and hence the species does not approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
Scottish Crossbill status Least Concern

Migration

Resident and dispersive. In most years, birds disperse after breeding to seek better food supplies, settling in adjacent or fairly close woods or plantations in Scottish highlands. When large populations build up after several years of successful breeding, birds sometimes move further in general exodus; e.g. in summer of 1936 many birds in upper Strathspey dispersed in large flocks, and few remained there to breed in spring 1937.

Distribution map

Scottish Crossbill distribution range map

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