Red Crossbill

Identification

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.<p>The distinctive crossed mandibles eliminate most other species, but this feature is shared by the similar two-barred crossbill, with which it overlaps considerably in range. The two-barred crossbill has two bright white wing bars, while the wings of the red crossbill are entirely brownish-black.<p>The red crossbill is the only dark-winged crossbill throughout most of its range, but it overlaps at least seasonally with the small ranges of the very similar parrot, Scottish, and Cassia crossbills. These species were formerly considered subspecies of the red crossbill, and though they show very slight differences in bill size and shape, they are very difficult to visually distinguish from the red crossbill and are generally best identified by call. The plumage differences between these four crossbills are negligible, there being more variation between individual birds than between species.<p>Measurements:

Taxonomy

The red crossbill was formally described by the Swedish naturalist Carl Linnaeus in 1758 in the tenth edition of his Systema Naturae under the binomial name Loxia curvirostra. Linnaeus specified the locality as Europe but this was restricted to Sweden by Ernst Hartert in 1904. The genus name Loxia is from Ancient Greek loxos, "crosswise"; and curvirostra is Latin for "curved bill".<p>The red crossbill is in the midst of an adaptive radiation into the niches presented by the various species of conifer. There are about 10 North American and 18 Eurasian types so far identified, with many known to affiliate with a particular conifer species or a suite of similar conifer species. While each type may be seen to feed on many different conifer species when not breeding, each has optimal breeding success only in a particular type of conifer forest. This isolates the populations against interbreeding, which over time has resulted in their diverging genetically, phenotypically, and even speciating. Birds of all types are essentially identical in appearance but have slight differences in their vocalizations. Typically they are identified by their single note "chip" calls, which they give frequently and which differ considerably between types. Often computer analysis is used to distinguish the call types, but experienced observers can learn to separate the more distinctive ones by ear in the field.<p>The different populations of red crossbill are referred to as "types" because they are differentiated by a phenotypic feature (call note) and not all of them have yet been proven to be genetically distinct. Those populations which have been found to be genetically distinct are considered subspecies. Three populations formerly considered to be subspecies of red crossbill are now recognized by most authorities as full species:<p>As research into the species has progressed, types are increasingly being found to be genetically distinct and elevated to the subspecies level. It is expected that this trend will continue, and it is also likely that more of these subspecies will eventually be recognized as full species.<p>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 (L. c. balearica) and the North African crossbill (L. c. poliogyna), feeding primarily on Aleppo pine (Pinus halepensis); the Cyprus crossbill (L. c. guillemardi), feeding primarily on European black pine (Pinus nigra); and an as-yet unidentified crossbill with a parrot crossbill-sized bill feeding primarily on Bosnian pine (Pinus heldreichii) 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.[citation needed]

Scientific name

Loxia curvirostra

Authority

Linnaeus, 1758

Order

Passeriformes

Family

Fringillidae

Genus

Loxia

Range and habitat

Breeding range

PAL, OR, NA, MA : subarctic to subtropical Holarctic conifer forest: British Is., Scandinavia (except far n) e across Russia to Sea of Okhotsk, Sakhalin and s Kuril Is. (se Russia), Hokkaido to c Honshu (n, c Japan), n Korean Pen., in s through Iberian Pen., Morocco to Tunisia (nw, nc Africa), e through Mediterranean, Turkey, Caucasus, Altai of e Kyrgyzstan, e Kazakhstan, nw Xinjiang (nw China), s, c Mongolia to Heilongjiang and Hebei (ne China); disjunctly wc to e Himalayas, se Tibet, Qinghai and Gansu to nw Yunnan; s Vietnam; Luzon (n Philippines); se Alaska e to Newfoundland (ne Canada), s to n Baja California (nw Mexico), Rocky and Appalachian mts., s through Nicaragua

Non-breeding range

irruptively southward

Migration

Resident species

Conservation

Population trend

stable