Editing Crossbill (section)

==Systematics and evolution==
The genus ''Loxia'' was introduced by the Swedish naturalist [[Carl Linnaeus]] in 1758 in the [[10th edition of Systema Naturae|10th edition]] of his ''[[Systema Naturae]]''.<ref>{{cite book | last=Linnaeus | first=C. | author-link=Carl Linnaeus | year=1758 | title= Systema Naturæ per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis | volume=1| edition=10th | page=171 | publisher=Holmiae:Laurentii Salvii  | language=la | url= https://www.biodiversitylibrary.org/page/727078 }}</ref> The name is from the [[Ancient Greek]] {{Transliteration|grc|loxos}}, "crosswise".<ref name =job>{{cite book | last= Jobling | first= James A. | year= 2010| title= The Helm Dictionary of Scientific Bird Names | publisher=Christopher Helm | location = London, United Kingdom | isbn = 978-1-4081-2501-4 | page = 231 | url=https://archive.org/stream/Helm_Dictionary_of_Scientific_Bird_Names_by_James_A._Jobling#page/n231/mode/1up}}</ref> The Swiss naturalist [[Conrad Gessner]] had used the word ''Loxia'' for a crossbill in 1555 in his ''[[Historia animalium (Gessner book)|Historiae Animalium]]''.<ref>{{cite book| last=Gesner | first=Conrad | author-link=Conrad Gessner | title=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 | year=1555 | publisher= Froschauer | location=Zurich | language=Latin | url=https://www.biodiversitylibrary.org/page/52661450 | pages=568}}</ref> The [[type species]] was designated as ''Loxia curvirostra'' ([[red crossbill]]) by [[George Robert Gray]] in 1840.<ref>{{ cite book | last=Gray | first=George Robert | author-link=George Robert Gray | year=1840 | title=A List of the Genera of Birds : with an Indication of the Typical Species of Each Genus | location=London | publisher=R. and J.E. Taylor | page=49 | url=http://biodiversitylibrary.org/page/13668938 }}</ref><ref>{{ cite book | editor-last=Paynter | editor-first=Raymond A. Jr | year=1968 | title=Check-List of Birds of the World | volume=14 | publisher=Museum of Comparative Zoology | place=Cambridge, Massachusetts | page=287 | url=https://www.biodiversitylibrary.org/page/14481488 }}</ref>

Analysis of [[mtDNA|mitochondrial]] [[cytochrome b|cytochrome ''b'']] [[DNA sequence|sequence]] data indicates that the crossbills and [[redpoll]]s share a common ancestor and only diverged during the [[Tortonian]] ({{circa|8 {{abbr|mya|million years ago}}}}, Late [[Miocene]]).<ref>{{cite journal | doi = 10.1007/PL00000930 | last1 = Arnaiz-Villena | first1 = A. | last2 = Guillén | first2 = J. | last3 = Ruiz-del-Valle | first3 = V. | last4 = Lowy | first4 = E. | last5 = Zamora | first5 = J. | last6 = Varela | first6 = P. | last7 = Stefani | first7 = D. | last8 = Allende | first8 = L. M. | year = 2001 | title = Phylogeography of crossbills, bullfinches, grosbeaks, and rosefinches | url = http://chopo.pntic.mec.es/~biolmol/publicaciones/crossbills.pdf | journal = Cellular and Molecular Life Sciences | volume = 58 | issue = 8| pages = 1159–1166 | pmid = 11529508 | s2cid = 6241573 }}</ref>  The research suggests that the genera ''Loxia'' and ''[[Carduelis]]'' might be merged into a single genus, for which the name ''[[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]]), it seems more appropriate to split up the genus ''Carduelis'' as it had already been done during most of the 20th century. Unfortunately, the fossil record is restricted to a [[Late Pliocene]] ({{circa|2 {{abbr|mya|million years ago}}}}) species, ''Loxia patevi'', found at [[Varshets]], Bulgaria.

The species of crossbills are difficult to separate, and care is needed even with the two-barred 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 two-barred crossbills are conspecific.

The identification problem is least severe in North America, where only the red and white-winged species occur, and (possibly) worst in the Scottish Highlands, where three species breed and the two-barred is also a possible vagrant.

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.<ref>[http://www.birds.cornell.edu/roundrobin/2011/08/02/science-at-work-how-many-kinds-of-red-crossbills-are-there-anyway/] (2011)</ref> Preliminary investigations in [[Europe]] and [[Asia]] suggest an equal, if not greater, complexity, with several different call types identified;<ref name="  Förschle" >{{cite journal| last1= Förschler | first1= Marc I.  |last2=Kalko |first2=Elisabeth K. V. | year=2009 | title= Vocal types in crossbill populations (''Loxia'' spp.) of Southwest Europe | journal=Journal of Ornithology | volume= 150 | pages= 17–27 | doi =10.1007/s10336-008-0312-z | s2cid= 13074563 }}</ref><ref name=robb >{{cite journal| last= Robb | first= Magnus S | year=2000 | title= Introduction to vocalizations of crossbills in north-western Europe | journal= Dutch Birding | volume=22 | issue= 2 | pages= 61–107 }}</ref> 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]] 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.<ref name= Summers >{{cite journal| last1= Summers | first1= R. W. | last2= Dawson|first2=R. J. |last3=Phillips|first3=R. E.| year= 2007| title= Assortative mating and patterns of inheritance indicate that the three crossbill taxa in Scotland are species| journal= Journal of Avian Biology | volume=38 | issue= 2| pages= 153–162 | doi = 10.1111/j.0908-8857.2007.03798.x}}</ref>

Currently accepted species<ref name=ioc>{{cite web| editor1-last=Gill | editor1-first=Frank | editor2-last=Donsker | editor2-first=David | title=Finches, euphonias | work= World Bird List Version 5.2| url=http://www.worldbirdnames.org/bow/finches/ | publisher=International Ornithologists' Union| access-date=5 June 2015 }}</ref> and their preferred food sources are:
{| class="wikitable"
|-
! Image !! Scientific name !! Common name!! Food source !! Distribution of species
|-
|[[File:Loxia curvirostra2.jpg|120px]]|| ''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]]
|-
|[[File:Loxia leucoptera Kittila 20110309.JPG|120px]]|| ''Loxia leucoptera''|| [[Two-barred crossbill]]|| Larch (''Larix'') species, particularly ''L. sibirica'', ''L. gmelinii'', ''L. laricina'' and (in North America) also [[Tsuga|hemlock]] (''Tsuga'') ||[[Eurasia]] and [[North America]]
|-
|[[File:Loxia megaplaga Smithsonian.jpg|frameless|120x120px]]
|''Loxia megaplaga''  || [[Hispaniolan crossbill]] || [[Hispaniolan pine]] (''Pinus occidentalis'') ||[[Hispaniola]] ([[Haiti]] and the [[Dominican Republic]])
|-
|[[File:Loxia pytyopsittacus, Budby Common 1.jpg|120px]]|| ''Loxia pytyopsittacus''|| [[Parrot crossbill]]||   [[Scots pine]] (''Pinus sylvestris'') ||[[Northern Europe|Northern]], [[Eastern Europe|Eastern]], and [[Central Europe]]
|-
|[[File:Scottish Crossbill from the Crossley ID Guide Britain and Ireland.jpg|frameless|121x121px]]
|''Loxia scotica'' || [[Scottish crossbill]] ||  Scots pine (''Pinus sylvestris'') and [[larch]] (''Larix'') species (particularly plantations of ''L. decidua'') ||[[Scotland]]
|-
|[[File:965.5 - CASSIA CROSSBILL (6-30-2018) trail n-w from upper penstamon c g, cassia co, id -17 male & juv (43245983821).jpg|120px]]|| ''Loxia sinesciuris''|| [[Cassia crossbill]] || Isolated population of the [[lodgepole pine]] (''Pinus contorta latifolia'') ||South Hills and [[Albion Mountains]], [[Idaho]], [[United States]]
|-
|}

Originally, the [[chestnut-backed sparrow-lark]] (''Eremopterix leucotis'') and [[Pine grosbeak]] (''Pinicola enucleator'') were also classified as belonging within the genus ''Loxia''.<ref>{{Cite web|url=http://avibase.bsc-eoc.org/species.jsp?lang=EN&avibaseid=9164F31438BE23C0|title=Eremopterix leucotis - Avibase|website=avibase.bsc-eoc.org|access-date=2016-11-18}}</ref>