# Crossbill

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Genus of birds

This article is about the genus of birds. For the lens series, see [Zeiss Loxia](/source/Zeiss_Loxia). For the medical condition, see [torticollis](/source/Torticollis).

Crossbill Red crossbill or common crossbill (Loxia curvirostra) Scientific classification Kingdom: Animalia Phylum: Chordata Class: Aves Order: Passeriformes Family: Fringillidae Subfamily: Carduelinae Genus: Loxia Linnaeus, 1758 Type species Loxia curvirostra Species Loxia curvirostra Loxia leucoptera Loxia megaplaga Loxia pytyopsittacus Loxia scotia Loxia sinesciuris †Loxia patevi

**Crossbills** are [birds](/source/Bird) of the [genus](/source/Genus) ***Loxia*** within the [finch](/source/Finch) family ([Fringillidae](/source/Fringillidae)), with six extant and one [extinct](/source/Bird_extinction) species. These birds are characterized by their mandibles with crossed tips, which gives the group its English name. Adult males tend to be red or orange in color, and females green or yellow, but there is much variation.

Crossbills are specialist feeders on [conifer](/source/Conifer) cones, and the unusual bill shape is an adaptation which enables them to extract seeds from cones. These birds are typically found in higher northern hemisphere latitudes, where their food sources grow. They irrupt out of the breeding range when the cone crop fails. Crossbills breed very early in the year, often in winter months, to take advantage of maximum cone supplies.

## Systematics and evolution

The genus *Loxia* was introduced by the Swedish naturalist [Carl Linnaeus](/source/Carl_Linnaeus) in 1758 in the [10th edition](/source/10th_edition_of_Systema_Naturae) of his *[Systema Naturae](/source/Systema_Naturae)*.[1] The name is from the [Ancient Greek](/source/Ancient_Greek) *loxos*, "crosswise".[2] The Swiss naturalist [Conrad Gessner](/source/Conrad_Gessner) had used the word *Loxia* for a crossbill in 1555 in his *[Historiae Animalium](/source/Historia_animalium_(Gessner_book))*.[3] The [type species](/source/Type_species) was designated as *Loxia curvirostra* ([red crossbill](/source/Red_crossbill)) by [George Robert Gray](/source/George_Robert_Gray) in 1840.[4][5]

Analysis of [mitochondrial](/source/MtDNA) [cytochrome *b*](/source/Cytochrome_b) [sequence](/source/DNA_sequence) data indicates that the crossbills share a common ancestor with the [redpoll](/source/Redpoll), which diverged during the [Tortonian](/source/Tortonian) (c. 8 mya, Late [Miocene](/source/Miocene)).[6] The research suggests that the genera *Loxia* and *[Carduelis](/source/Carduelis)* might be merged into a single genus, for which the name *[Loxia](/source/Loxia)* would then have priority. But this would imply changing the name of a large number of species, and given that the adaptations of the crossbills represent a unique evolutionary path (see [Evolutionary grade](/source/Evolutionary_grade)), it seems more appropriate to split up the genus *Carduelis* as it had already been done during most of the 20th century. The fossil record of *Loxia* is restricted to a [Late Pliocene](/source/Late_Pliocene) (c. 2 mya) species, *Loxia patevi*, found at [Varshets](/source/Varshets), Bulgaria.

The species of crossbills are difficult to separate, and care is needed even with the white-winged and Hispaniolan crossbills, the easiest. The other species are identified by subtle differences in head shape and bill size, and the identification problems formerly led to much taxonomic speculation, with some scientists considering that the parrot and Scottish crossbills and possibly the Hispaniolan and white-winged crossbills are conspecific.

The identification problem is least severe in North America, where only the red, white-winged and (locally) Cassia species occur, and (possibly) the most challenging in the [Scottish Highlands](/source/Scottish_Highlands), where three similar-looking species breed and the two-barred (known as white-winged in North America) is a possible [vagrant](/source/Vagrancy_(biology)).

Work on vocalization in North America suggests that there are eight or nine discrete populations of red crossbill in that continent alone, which do not interbreed and are (like the named species) adapted to specialize in different conifer species. While several ornithologists seem inclined to give these forms species status, no division of the American red crossbills has yet occurred.[7] Preliminary investigations in [Europe](/source/Europe) and [Asia](/source/Asia) suggest an equal, if not greater, complexity, with several different call types identified;[8][9] these call types being as different from each other as from the named species of the parrot and Scottish crossbills - suggesting either that they *are* valid species, or else that the parrot and Scottish crossbills may *not* be.

Genetic research on their [DNA](/source/DNA) failed to reveal any difference between any of the crossbills (including the morphologically distinct two-barred), with variation between individuals greater than any difference between the taxa. This led to the suggestion that *limited* interbreeding between the different types prevented significant genetic differentiation, and enabled each type to maintain a degree of morphological plasticity, which may be necessary to enable them to feed on different conifers when their preferred food species has a crop failure. Research in Scotland, however, has shown that the parrot and Scottish crossbills are reproductively isolated from each other and also from the red crossbill, despite irruption of that species into their ranges, and the diagnostic calls and bill dimensions have not been lost. They are, therefore, good species.[10]

Currently accepted species[11] and their preferred food sources are:

Image Scientific name Common name Food source Distribution of species Loxia curvirostra Red crossbill Spruce (Picea) species; some populations (distinct species?) on various pine (Pinus) species and (in western North America) Douglas fir Eurasia, North Africa, and North America Loxia leucoptera Two-barred crossbill Larch (Larix) species, particularly L. sibirica, L. gmelinii, L. laricina and (in North America) also hemlock (Tsuga) Eurasia and North America Loxia megaplaga Hispaniolan crossbill Hispaniolan pine (Pinus occidentalis) Hispaniola (Haiti and the Dominican Republic) Loxia pytyopsittacus Parrot crossbill Scots pine (Pinus sylvestris) Northern, Eastern, and Central Europe Loxia scotica Scottish crossbill Scots pine (Pinus sylvestris) and larch (Larix) species (particularly plantations of L. decidua) Scotland Loxia sinesciuris Cassia crossbill Isolated population of the lodgepole pine (Pinus contorta latifolia) South Hills and Albion Mountains, Idaho, United States †Loxia patevi Loxia patevi Unknown Fossils dated to the Late Pliocene are known from Varshets, Bulgaria

Originally, several species such as the [chestnut-backed sparrow-lark](/source/Chestnut-backed_sparrow-lark) (*Eremopterix leucotis*),[12] [pine grosbeak](/source/Pine_grosbeak) (*Pinicola enucleator*) and [northern cardinal](/source/Northern_cardinal) (*Cardinalis cardinalis*)[13] were also included in *Loxia*.

## Feeding behavior

[Red crossbill](/source/Red_crossbill) skull and jaw anatomy from [William Yarrell](/source/William_Yarrell)'s *[A History of British Birds](/source/A_History_of_British_Birds_(Yarrell_book))* (1843)

The different species specialize in feeding on different conifer species, with the bill shape optimized for opening that species of conifer. This is achieved by inserting the bill between the conifer cone scales and twisting the lower mandible towards the side to which it crosses, enabling the bird to extract the seed at the bottom of the scale with its tongue.

The mechanism by which the bill-crossing is developed (which usually, but not always, occurs in a 1:1 frequency of left-crossing or right-crossing [morphs](/source/Morph_(zoology))), and what determines the direction, has hitherto withstood all attempts to resolve it.

It is very probable that there is a genetic basis underlying the phenomenon (young birds whose bills are still straight will give a cone-opening behavior if their bills are gently pressed, and the crossing develops before the birds are fledged and feeding independently), but at least in the red crossbill (the only species which has been somewhat thoroughly researched regarding this question) there is no straightforward mechanism of [heritability](/source/Heritability).

While the direction of crossing seems to be the result of at least three genetic factors working together in a case of [epistasis](/source/Epistasis) and most probably [autosomal](/source/Autosomal), it is not clear whether the 1:1 frequency of both morphs in most cases is the result of genetics or environmental selection. Populations that feed on cones without removing or twisting them will likely show a 1:1 morph distribution, no matter what the genetic basis may be: the [fitness](/source/Fitness_(biology)) of each morph is inversely proportional to its frequency in the population. Such birds can only access the cone with the lower mandible tip pointing *towards* it to successfully extract seeds, and thus a too high number of birds of one morph will result in the food availability for each bird of this morph decreasing.[14]

They can utilize other conifers to their preferred, and often need to do so when their preferred species has a crop failure, but are less efficient in their feeding (not enough to prevent survival, but probably enough to reduce breeding success).

## Fossil record

*[Loxia patevi](/source/Loxia_patevi)* was described from the [Late Pliocene](/source/Late_Pliocene) of [Varshets](/source/Varshets), Bulgaria.[15]

## References

1. **[^](#cite_ref-1)** [Linnaeus, C.](/source/Carl_Linnaeus) (1758). [*Systema Naturæ per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis*](https://www.biodiversitylibrary.org/page/727078) (in Latin). Vol. 1 (10th ed.). Holmiae:Laurentii Salvii. p. 171.{{[cite book](https://en.wikipedia.org/wiki/Template:Cite_book)}}: CS1 maint: publisher location ([link](https://en.wikipedia.org/wiki/Category:CS1_maint:_publisher_location))

1. **[^](#cite_ref-job_2-0)** Jobling, James A. (2010). [*The Helm Dictionary of Scientific Bird Names*](https://archive.org/stream/Helm_Dictionary_of_Scientific_Bird_Names_by_James_A._Jobling#page/n231/mode/1up). London, United Kingdom: Christopher Helm. p. 231. [ISBN](/source/ISBN_(identifier)) [978-1-4081-2501-4](https://en.wikipedia.org/wiki/Special:BookSources/978-1-4081-2501-4).

1. **[^](#cite_ref-3)** [Gesner, Conrad](/source/Conrad_Gessner) (1555). [*Historiae animalium liber III qui est de auium natura. Adiecti sunt ab initio indices alphabetici decem super nominibus auium in totidem linguis diuersis: & ante illos enumeratio auium eo ordiné quo in hoc volumine continentur*](https://www.biodiversitylibrary.org/page/52661450) (in Latin). Zurich: Froschauer. p. 568.

1. **[^](#cite_ref-4)** [Gray, George Robert](/source/George_Robert_Gray) (1840). [*A List of the Genera of Birds : with an Indication of the Typical Species of Each Genus*](http://biodiversitylibrary.org/page/13668938). London: R. and J.E. Taylor. p. 49.

1. **[^](#cite_ref-5)** Paynter, Raymond A. Jr, ed. (1968). [*Check-List of Birds of the World*](https://www.biodiversitylibrary.org/page/14481488). Vol. 14. Cambridge, Massachusetts: Museum of Comparative Zoology. p. 287.

1. **[^](#cite_ref-6)** Arnaiz-Villena, A.; Guillén, J.; Ruiz-del-Valle, V.; Lowy, E.; Zamora, J.; Varela, P.; Stefani, D.; Allende, L. M. (2001). ["Phylogeography of crossbills, bullfinches, grosbeaks, and rosefinches"](http://chopo.pntic.mec.es/~biolmol/publicaciones/crossbills.pdf) (PDF). *Cellular and Molecular Life Sciences*. **58** (8): 1159–1166. [doi](/source/Doi_(identifier)):[10.1007/PL00000930](https://doi.org/10.1007%2FPL00000930). [PMID](/source/PMID_(identifier)) [11529508](https://pubmed.ncbi.nlm.nih.gov/11529508). [S2CID](/source/S2CID_(identifier)) [6241573](https://api.semanticscholar.org/CorpusID:6241573).

1. **[^](#cite_ref-7)** [\[1\]](https://www.birds.cornell.edu/roundrobin/2011/08/02/science-at-work-how-many-kinds-of-red-crossbills-are-there-anyway/) (2011)

1. **[^](#cite_ref-Förschle_8-0)** Förschler, Marc I.; Kalko, Elisabeth K. V. (2009). "Vocal types in crossbill populations (*Loxia* spp.) of Southwest Europe". *Journal of Ornithology*. **150**: 17–27. [doi](/source/Doi_(identifier)):[10.1007/s10336-008-0312-z](https://doi.org/10.1007%2Fs10336-008-0312-z). [S2CID](/source/S2CID_(identifier)) [13074563](https://api.semanticscholar.org/CorpusID:13074563).

1. **[^](#cite_ref-robb_9-0)** Robb, Magnus S (2000). "Introduction to vocalizations of crossbills in north-western Europe". *Dutch Birding*. **22** (2): 61–107.

1. **[^](#cite_ref-Summers_10-0)** Summers, R. W.; Dawson, R. J.; Phillips, R. E. (2007). "Assortative mating and patterns of inheritance indicate that the three crossbill taxa in Scotland are species". *Journal of Avian Biology*. **38** (2): 153–162. [doi](/source/Doi_(identifier)):[10.1111/j.0908-8857.2007.03798.x](https://doi.org/10.1111%2Fj.0908-8857.2007.03798.x).

1. **[^](#cite_ref-ioc_11-0)** Gill, Frank; Donsker, David (eds.). ["Finches, euphonias"](http://www.worldbirdnames.org/bow/finches/). *World Bird List Version 5.2*. International Ornithologists' Union. Retrieved 5 June 2015.

1. **[^](#cite_ref-12)** ["Eremopterix leucotis - Avibase"](http://avibase.bsc-eoc.org/species.jsp?lang=EN&avibaseid=9164F31438BE23C0). *avibase.bsc-eoc.org*. Retrieved 2016-11-18.

1. **[^](#cite_ref-13)** [Linnaeus, Carl](/source/Carl_Linnaeus) (1758). [*Systema naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. T(Laurentii Salvii)*](https://www.biodiversitylibrary.org/item/10277#page/3/mode/1up) (in Latin). Vol. 1. p. 824.

1. **[^](#cite_ref-14)** Edelaar, Pim; Postma, Erik; Knops, Peter; Phillips, Ron (2005). ["No support of a genetic basis of mandible crossing direction in crossbills (*Loxia* spp.)"](https://pure.knaw.nl/portal/files/469590/Edelaar_ea_3754.pdf) (PDF). *Auk*. **122** (4): 1123–1129. [doi](/source/Doi_(identifier)):[10.1642/0004-8038(2005)122\[1123:NSFAGB\]2.0.CO;2](https://doi.org/10.1642%2F0004-8038%282005%29122%5B1123%3ANSFAGB%5D2.0.CO%3B2). [hdl](/source/Hdl_(identifier)):[20.500.11755/488d3732-6dd9-49f2-be2a-efcbfec9e08d](https://hdl.handle.net/20.500.11755%2F488d3732-6dd9-49f2-be2a-efcbfec9e08d). [JSTOR](/source/JSTOR_(identifier)) [4090517](https://www.jstor.org/stable/4090517).

1. **[^](#cite_ref-15)** Boev, Z. 1999. Earliest finds of crossbills (genus *Loxia*) (Aves: Fringillidae) from Varshets (NW Bulgaria). - Geologica balcanica, 29 (3-4): 51-57.

## External links

- [Crossbill videos, photos and sounds](http://ibc.lynxeds.com/family/finches-crossbills-allies-fringillidae) on the Internet Bird Collection

- ["Crossbill"](https://en.wikisource.org/wiki/1911_Encyclop%C3%A6dia_Britannica/Crossbill). *[Encyclopædia Britannica](/source/Encyclop%C3%A6dia_Britannica_Eleventh_Edition)*. Vol. 7 (11th ed.). 1911. p. 509.

v t e Genera of finches, sparrows and tanagers Kingdom: Animalia Phylum: Chordata Class: Aves Suborder: Passeri Infraorder: Passerida Superfamily: Passeroidea Passeroidea Estrildidae Amandavinae Amadina Amandava Ortygospiza Erythrurinae Chloebia Erythrura Estrildinae Brunhilda Coccopygia Cryptospiza Delacourella Estrilda Glaucestrilda Mandingoa Nesocharis Nigrita Parmoptila Lagonostictinae Clytospiza Euschistospiza Granatina Hypargos Lagonosticta Pyrenestes Pytilia Spermophaga Uraeginthus Lonchurinae Euodice Lepidopygia Lonchura Mayrimunia Padda Spermestes Poephilinae Aidemosyne Bathilda Emblema Heteromunia Neochmia Oreostruthus Poephila Stagonopleura Stizoptera Taeniopygia Passeridae Carpospiza Gymnoris Hypocryptadius Montifringilla Onychostruthus Passer Petronia Pyrgilauda Ploceidae Amblyospiza Anaplectes Brachycope Bubalornis Dinemellia Euplectes Foudia Histurgops Malimbus Philetairus Plocepasser Ploceus Pseudonigrita Quelea Sporopipes Prunellidae Prunella Urocynchramidae Urocynchramus Viduidae Anomalospiza Vidua Nine-primaried oscines See below ↓ Nine-primaried oscines Fringillidae Carduelinae Acanthis Agraphospiza †Aidemedia †Akialoa Bucanetes Callacanthis Carduelis Carpodacus †Chloridops Chloris Chlorodrepanis Chrysocorythus †Ciridops Coccothraustes Crithagra Drepanis †Dysmorodrepanis Eophona Haemorhous Hemignathus Hesperiphona Himatione Leucosticte Linaria Linurgus Loxia Loxioides Loxops Magumma †Melamprosops Mycerobas Oreomystis †Orthiospiza Palmeria Paroreomyza Pinicola Procarduelis Pseudonestor †Psittirostra Pyrrhula Pyrrhoplectes †Rhodacanthis Rhodopechys Rhodospiza Rhynchostruthus Serinus Spinus Telespiza †Vangulifer †Viridonia †Xestospiza Euphoniinae Chlorophonia Euphonia Fringillinae Fringilla Motacillidae Anthus Dendronanthus Macronyx Motacilla Tmetothylacus Peucedramidae Peucedramus Emberizoidea See below ↓ Emberizoidea Calcariidae Calcarius Plectrophenax Rhynchophanes Calyptophilidae Calyptophilus Cardinalidae Amaurospiza Cardinalis Caryothraustes Chlorothraupis Cyanocompsa Cyanoloxia Granatellus Habia Passerina Periporphyrus Pheucticus Piranga Spiza Emberizidae Emberiza Icteridae See below ↓ Icteriidae Icteria Mitrospingidae Lamprospiza Mitrospingus Orthogonys Nesospingidae Nesospingus Parulidae Basileuterus Cardellina Catharopeza Geothlypis Helmitheros Leucopeza Leiothlypis Limnothlypis Mniotilta Myioborus Myiothlypis Oporornis Oreothlypis Parkesia Protonotaria Seiurus Setophaga Vermivora Passerellidae Aimophila Ammodramus Ammospiza Amphispiza Amphispizopsis Arremon Arremonops Artemisiospiza Atlapetes Calamospiza Centronyx Chlorospingus Chondestes Junco Melospiza Melozone Oreothraupis Oriturus Passerculus Passerella †Pedinorhis Peucaea Pezopetes Pipilo Pooecetes Rhynchospiza Spizella Spizelloides Torreornis Xenospiza Zonotrichia Phaenicophilidae Microligea Phaenicophilus Xenoligea Rhodinocichlidae Rhodinocichla Spindalidae Spindalis Teretistridae Teretistris Thraupidae See below ↓ Icteridae incertae sedis †Cremaster †Pandanaris †Pyelorhamphus Agelaiinae Agelaioides Agelaius Agelasticus Amblyramphus Anumara Chrysomus Curaeus Dives Euphagus Gnorimopsar Gymnomystax Hypopyrrhus Lampropsar Macroagelaius Molothrus Nesopsar Oreopsar Pseudoleistes Ptiloxena Quiscalus Xanthopsar Amblycercinae Amblycercus Cassicinae Cacicus Cassiculus Psarocolius Dolichonychinae Dolichonyx Icterinae Icterus Sturnellinae Leistes Sturnella Xanthocephalinae Xanthocephalus Thraupidae Catamblyrhynchinae Catamblyrhynchus Charitospizinae Charitospiza Parkerthraustes Coerebinae Asemospiza Camarhynchus Certhidea Coereba Euneornis Geospiza Loxigilla Loxipasser Melanospiza Melopyrrha Phonipara Pinaroloxias Platyspiza Tiaris Dacninae Cyanerpes Dacnis Tersina Diglossinae Acanthidops Catamenia Conirostrum Diglossa Geospizopsis Haplospiza Idiopsar Melanodera Nesospiza Phrygilus Rowettia Sicalis Xenodacnis Emberizoidinae Coryphaspiza Emberizoides Embernagra Hemithraupinae Chrysothlypis Chlorophanes Hemithraupis Heterospingus Iridophanes Nemosiinae Compsothraupis Cyanicterus Nemosia Sericossypha Orchesticinae Orchesticus Poospizinae Castanozoster Cnemoscopus Cypsnagra Donacospiza Kleinothraupis Microspingus Nephelornis Piezorina Poospiza Poospizopsis Pseudospingus Sphenopsis Thlypopsis Urothraupis Xenospingus Porphyrospizinae Incaspiza Rhopospina Saltatorinae Saltator Saltatricula Sporophilinae Sporophila Tachyphoninae Conothraupis Coryphospingus Creurgops Eucometis Heliothraupis Lanio Loriotus Ramphocelus Rhodospingus Tachyphonus Trichothraupis Volatinia Thraupinae Anisognathus Bangsia Buthraupis Calochaetes Chalcothraupis Chlorochrysa Chlorornis Cissopis Cnemathraupis Diuca Dubusia Iridosornis Ixothraupis Lophospingus Neothraupis Paroaria Pipraeidea Poecilostreptus Pseudosaltator Rauenia Schistochlamys Sporathraupis Stephanophorus Stilpnia Tangara Tephrophilus Thraupis Wetmorethraupis

Taxon identifiers Loxia Wikidata: Q339517 Wikispecies: Loxia ADW: Loxia BOLD: 4781 CoL: 5GX7 EoL: 45510343 EPPO: 1LOXIG EURING: 16689 Fauna Europaea: 97450 Fauna Europaea (new): 1cd829a8-02f2-41cd-86cc-a65ea528e6ba GBIF: 2494150 iNaturalist: 10410 IRMNG: 1315717 ITIS: 179258 NBN: NHMSYS0000530453 NCBI: 64794 Open Tree of Life: 157601 Paleobiology Database: 161534 Plazi: DD05F16A-8D95-787E-CA1B-9F566C107347 WoRMS: 1461959 ZooBank: D623CA02-9E5A-4800-B479-F71BD16C1C1F

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Adapted from the Wikipedia article [Crossbill](https://en.wikipedia.org/wiki/Crossbill) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Crossbill?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.