Red crossbill
The red crossbill is a small passerine bird in the finch family Fringillidae, also known as the common crossbill in Eurosiberia. Crossbills have distinctive mandibles, crossed at the tips, which enable them to extract seeds from conifer cones and other fruits.
Adults are often brightly coloured, with red or orange males and green or yellow females, but there is wide variation in colour, beak size and shape, and call types, leading to different classifications of variants, some of which have been named as subspecies.
Description
Crossbills are characterized by the mandibles crossing at their tips, which gives the group its English name. Using their crossed mandibles for leverage, crossbills are able to efficiently separate the scales of conifer cones and extract the seeds on which they feed. Adult males tend to be red or orange in colour, and females green or yellow, but there is much variation.In North America, nine distinct red crossbill variants differing in vocalizations as well as beak size and shape are recognized. Each call type evolved to specialize on different species of conifer.
Breeding and irruption
The red crossbill breeds in the spruce forests of North America, as well as Europe and Asia. Some populations breed in pine forests in certain areas of all three continents, and in North America, also in Douglas fir. It nests in conifers, laying 3–5 eggs.in his Chronica Majora of a crossbill holding a fruit in its beak, with the Latin words Alaudis parum majores.
This crossbill is mainly resident, but often irrupts south when its food source fails. These irruptions led in the twentieth century to the establishment of permanent breeding colonies in England, and more recently in Ireland. This species forms flocks outside the breeding season, often mixed with other crossbills.
The first known irruption, recorded in England by the chronicler Matthew Paris, was in 1254; the next, also in England, appears to have been in 1593. The engraver Thomas Bewick wrote that "It sometimes is met with in great numbers in this country, but its visits are not regular", adding that many hundreds arrived in 1821. Bewick then cites Matthew Paris as writing "In 1254, in the fruit season, certain wonderful birds, which had never before been seen in England, appeared, chiefly in the orchards. They were a little bigger than Larks, and eat the pippins of the apples ' but no other part of them... They had the parts of the beak crossed ' by which they divided the apples as with a forceps or knife. The parts of the apples which they left were as if they had been infected with poison." Bewick further records an account by Sir Roger Twysden for the Additions to the Additamenta of Matt. Paris "that in the apple season of 1593, an immense multitude of unknown birds came into England... swallowing nothing but the pippins, and for the purpose of dividing the apple, their beaks were admirably adapted by nature, for they turn back, and strike one point upon the other, so as to show... the transverse sickles, one turned past the other."
Taxonomy and systematics
The genus name Loxia is from Ancient Greek loxos, "crosswise", and curvirostra is Latin for "curved bill".This species is difficult to separate from the parrot crossbill and Scottish crossbill, both of which breed within its Eurasian range, as plumage distinctions from those two species are negligible, though the head and bill are smaller than in either of the other species. Care is needed in identification, especially in Eurasia, where the glip or chup call is probably the best indicator. The identification problem is less severe in North America, where only the red crossbill and white-winged crossbill occur. However, there has been debate as to whether different call types should be considered separate species. For example, the Cassia crossbill, occurring in the South Hills and Albion Mountains in Idaho, has been described as a new species because it shows a very low degree of hybridization with the red crossbill. There are also genetic differences between the call type populations. Nevertheless, few ornithologists have chosen to give these forms species status.
Some large-billed, pine-feeding populations currently assigned to this species in the Mediterranean area may possibly be better referred to either the parrot crossbill or to new species in their own right, but more research is needed. These include the Balearic crossbill and the North African crossbill, feeding primarily on Aleppo pine ; the Cyprus crossbill, feeding primarily on European black pine ; and an as-yet unidentified crossbill with a parrot crossbill-sized bill feeding primarily on Bosnian pine in the Balkans. These populations also differ on plumage, with the Balearic, North African and Cyprus subspecies having yellower males, and the Balkan type having deep purple-pink males; this, however, merely reflects the differing anthocyanin content of the cones they feed on, as these pigments are transferred to the feathers.
Diversity
| Distinct Eurasian common crossbill populations | Associated tree species | Summers' list based on calls | The Sound Approachs list based on calls | Call-type, flight call |
| Balearic crossbill, L. c. balearica | Aleppo pine | |||
| North African crossbill, L. c. poliogyna | Aleppo pine | 3E | ||
| Corsican crossbill, L. c. corsicana | European black pine | |||
| Cyprus, Turkey + Caucasus crossbill, L. c. guillemardi | European black pine | 5D | ||
| Crimean crossbill, L. c. mariae | European black pine | |||
| Luzon crossbill, L. c. luzoniensis | Khasi pine | |||
| Annam crossbill, L. c. meridionalis | Khasi pine | |||
| Altai crossbill, L. c. altaiensis | Spruces | |||
| Tian Shan crossbill, L. c. tianschanica | Schrenk's spruce | |||
| Himalayan crossbill, L. c. himalayensis | Himalayan hemlock | |||
| Japanese crossbill, L. c. japonica | ||||
| Other Eurasian crossbills' | ||||
| 1A | 'British crossbill' | Type E - flight call "Chip" | ||
| 1B | 'Parakeet crossbill' | Type X - flight call "Cheep" | ||
| 2B | 'Wandering crossbill' | Type A - flight call "Keep" | ||
| Parrot crossbill, Loxia ptyopsittacus | Scots pine | 2D | ||
| Scottish crossbill, Loxia scotica | Scots pine, larches, lodgepole pine | 3C | ||
| 'Bohemian crossbill' | Type B - flight call "Weet" | |||
| 4E | 'Glip crossbill' | Type C - flight call "Glip" | ||
| 'Phantom crossbill' | Type D - flight call "Jip" | |||
| 'Scarce crossbill' | Type F - flight call "Trip" |
| North American red crossbill subspecies based on biometrics | Jeff Groth's list using call types | Recorded on tree species |
| Newfoundland crossbill, L. c. percna | Type 8 | black spruce |
| Lesser crossbill, L. c. minor | Type 3 | western hemlock |
| Sitka crossbill, L. c. sitkensis | Type 3 | ditto |
| L. c. neogaea | Type 1 | Tsuga species, Picea glauca, Pinus strobus |
| L. c. neogaea | Type 4 | Douglas fir |
| Rocky Mountain crossbill, L. c. benti | Types 2, 7 | Type 2: Rocky Mountains ponderosa pine in the west, various Pinus species in the east; Type 7: possibly a general diet |
| Sierra crossbill, L. c. grinnelli | Type 2, 7 | ditto |
| Bendire's crossbill, L. c. bendirei | Type 2, 7 | ditto |
| Mexican crossbill, L. c. stricklandi | Type 6 | pine species in section Trifoliae |
| Central American crossbill, L. c. mesamericana | ||
| Cassia crossbill | Type 9 | isolated population of the lodgepole pine |