Red Crossbill
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The red crossbill or common crossbill (''Loxia curvirostra'') is a small
passerine A passerine () is any bird of the order Passeriformes (; from Latin 'sparrow' and '-shaped'), which includes more than half of all bird species. Sometimes known as perching birds, passerines are distinguished from other orders of birds by t ...
bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...
in the
finch The true finches are small to medium-sized passerine birds in the family Fringillidae. Finches have stout conical bills adapted for eating seeds and nuts and often have colourful plumage. They occupy a great range of habitats where they are usua ...
family Fringillidae. 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 beak size and shape, and call types, leading to different classifications of variants, some of which have been named as subspecies. The species is known as "red crossbill" in North America and "common crossbill" in Europe.


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.


Identification

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. 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 Parrots, also known as psittacines (), are birds of the roughly 398 species in 92 genera comprising the order Psittaciformes (), found mostly in tropical and subtropical regions. The order is subdivided into three superfamilies: the Psittacoid ...
, 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. Measurements: * Length: 20 cm * Weight: 40-53 g * Wingspan: 27–29 cm


Breeding and irruption

Red crossbills breed in a variety of coniferous forests across
North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...
and
Eurasia Eurasia (, ) is the largest continental area on Earth, comprising all of Europe and Asia. Primarily in the Northern and Eastern Hemispheres, it spans from the British Isles and the Iberian Peninsula in the west to the Japanese archipelago a ...
. Its movements and occurrence are linked very closely to the availability of
conifer Conifers are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single ...
seeds, its primary food source. They typically nest in late summer (June–September) when the seeds of most conifer species mature, but may nest at any time of year if they locate an area with a suitable cone crop. This species is considered nomadic and highly irruptive, as conifer seed production may vary considerably year to year and birds disperse widely to breed and forage when the cone crop in their particular vicinity fails. In many areas of their range they are considered irregular because they may be present in certain years and not in others. The various types of red crossbill (see Taxonomy and Systematics) prefer different types of conifers, and therefore may differ in the regularity, timing, and direction of their irruptions. A few populations, such as the Newfoundland crossbill (North American type 8), are resident and do not undertake significant movements. When they are not breeding, the various types of red crossbill may flock together, and may also flock with other species of crossbill. Red crossbill irruptions in the
British Isles The British Isles are a group of islands in the North Atlantic Ocean off the north-western coast of continental Europe, consisting of the islands of Great Britain, Ireland, the Isle of Man, the Inner and Outer Hebrides, the Northern Isles, ...
occur very infrequently, and were remarked upon by writers dating back to the 13th century. These irruptions led in the twentieth century to the establishment of permanent breeding colonies in England, and more recently in Ireland. The first known irruption, recorded in England by the chronicler
Matthew Paris Matthew Paris, also known as Matthew of Paris ( la, Matthæus Parisiensis, lit=Matthew the Parisian; c. 1200 – 1259), was an English Benedictine monk, chronicler, artist in illuminated manuscripts and cartographer, based at St Albans Abbey ...
, was in 1254; the next, also in England, appears to have been in 1593 (by which time the earlier irruption had apparently been entirely forgotten, since the crossbills were described as "unknown" in England). The engraver
Thomas Bewick Thomas Bewick (c. 11 August 17538 November 1828) was an English wood-engraver and natural history author. Early in his career he took on all kinds of work such as engraving cutlery, making the wood blocks for advertisements, and illustrating ch ...
wrote that "It sometimes is met with in great numbers in this country, but its visits are not regular",. Roger Twysden's Latin note on the 1593 outbreak is given in William Wats's edition of Paris's ''Chronica Majora'' (London, 1640). 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 '' omorum grana' but no other part of them... They had the parts of the beak crossed '' ancellatas' 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 Sir Roger Twysden, 2nd Baronet (21 August 1597 – 27 June 1672), of Roydon Hall near East Peckham in Kent, was an English historian and politician who sat in the House of Commons at various times between 1625 and 1640. Life Twysden was the son ...
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, '' ranella ipsa sive acinos' 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
sickle A sickle, bagging hook, reaping-hook or grasshook is a single-handed agricultural tool designed with variously curved blades and typically used for harvesting, or reaping, grain crops or cutting succulent forage chiefly for feeding livestock, ei ...
s, one turned past the other."


Taxonomy and systematics

The red crossbill was formally described by the Swedish naturalist
Carl Linnaeus Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his ennoblement in 1761 as Carl von Linné Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalised binomial nomenclature, the ...
in 1758 in the tenth edition of his ''
Systema Naturae ' (originally in Latin written ' with the ligature æ) is one of the major works of the Swedish botanist, zoologist and physician Carl Linnaeus (1707–1778) and introduced the Linnaean taxonomy. Although the system, now known as binomial nomen ...
'' under the
binomial name In taxonomy, binomial nomenclature ("two-term naming system"), also called nomenclature ("two-name naming system") or binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, bot ...
''Loxia curvirostra''. Linnaeus specified the
locality Locality may refer to: * Locality (association), an association of community regeneration organizations in England * Locality (linguistics) * Locality (settlement) * Suburbs and localities (Australia), in which a locality is a geographic subdivis ...
as Europe but this was restricted to Sweden by
Ernst Hartert Ernst Johann Otto Hartert (29 October 1859 – 11 November 1933) was a widely published German ornithologist. Life and career Hartert was born in Hamburg, Germany on 29 October 1859. In July 1891, he married the illustrator Claudia Bernadine E ...
in 1904. The genus name ''Loxia'' is from
Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic peri ...
, "crosswise"; and ''curvirostra'' is
Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
for "curved bill". The red crossbill is in the midst of an
adaptive radiation In evolutionary biology, adaptive radiation is a process in which organisms diversify rapidly from an ancestral species into a multitude of new forms, particularly when a change in the environment makes new resources available, alters biotic int ...
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 {{About, , the linguistics term dealing with languages unrelated to any other language in the world, Language isolate, other uses, Isolate (disambiguation){{!Isolate Isolates is a term used in developmental psychology and family studies, to describ ...
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. The different populations of red crossbill are referred to as "types" because they are differentiated by a
phenotypic In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological proper ...
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 In biological classification, subspecies is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (morphology), but that can successfully interbreed. Not all species ...
. Three populations formerly considered to be subspecies of red crossbill are now recognized by most authorities as full
species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
: *
Scottish Crossbill The Scottish crossbill (''Loxia scotica'') is a small passerine bird in the finch family Fringillidae. It is endemic to the Caledonian Forests of Scotland, and is the only terrestrial vertebrate species endemic to the United Kingdom. The Scottish ...
(''Loxia scotica'') -- Formerly Eurasian type 3C *
Parrot Crossbill The parrot crossbill (''Loxia pytyopsittacus'') is a small passerine bird in the finch family Fringillidae. It breeds in pine forests in northern and northeastern Europe. Taxonomy The parrot crossbill was formerly described in 1793 by the German ...
(''Loxia ptyopsittacus'') -- Formerly Eurasian type 2D * Cassia Crossbill (''Loxia sinesciuris'') -- Formerly North American type 9 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. Some large-billed, pine-feeding populations currently assigned to this species in the
Mediterranean The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the e ...
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'', the Austrian pine or black pine, is a moderately variable species of pine, occurring across Southern Europe from the Iberian Peninsula to the eastern Mediterranean, on the Anatolian peninsula of Turkey, Corsica and Cyprus, as wel ...
(''Pinus nigra''); and an as-yet unidentified crossbill with a parrot crossbill-sized bill feeding primarily on
Bosnian pine ''Pinus heldreichii'' (synonym ''P. leucodermis''; family Pinaceae), the Bosnian pine or Heldreich’s pine, is a species of pine native to mountainous areas of the Balkans and southern Italy. Description It is an evergreen tree up to in height ...
(''Pinus heldreichii'') in the
Balkans The Balkans ( ), also known as the Balkan Peninsula, is a geographical area in southeastern Europe with various geographical and historical definitions. The region takes its name from the Balkan Mountains that stretch throughout the who ...
. 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 Anthocyanins (), also called anthocyans, are water-soluble vacuolar pigments that, depending on their pH, may appear red, purple, blue, or black. In 1835, the German pharmacist Ludwig Clamor Marquart gave the name Anthokyan to a chemical compo ...
content of the cones they feed on, as these pigments are transferred to the feathers.


Diversity


References


External links

*
Ageing and sexing (PDF; 2.9 MB) by Javier Blasco-Zumeta & Gerd-Michael Heinze
{{Taxonbar, from=Q26552 red crossbill Holarctic birds red crossbill red crossbill Extant Late Pleistocene first appearances