The Common Crossbill (Loxia curvirostra) is a small passerine bird in the finch family Fringillidae. It breeds in the spruce forests of North America, where it is known as Red Crossbill, as well as Europe and Asia; some populations (different species?) 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.
This crossbill is mainly resident, but will regularly erupt south if its food source fails. This species will form flocks outside the breeding season, often mixed with other crossbills.
The crossbills are characterised by the mandibles crossing at their tips, which gives the group its English name. They are specialist feeders on conifer cones, particularly the various spruce species but also some populations (different species?) in Douglas-fir and various pine species, and the unusual bill shape is an adaptation to assist the extraction of the seeds from the cone.
Adult males tend to be red or orange in colour, and females green or yellow, but there is much variation.
This species is difficult to separate from Parrot Crossbill and Scottish Crossbill, both of which breed within its Eurasian range. The identification problem is less severe in North America, where only Red Crossbill and White-winged Crossbill occur.
Plumage distinctions from Parrot and Scottish Crossbills are negligible. The head and bill are smaller than in either of the other species. Care is needed to identify this species. The glip or chup call is probably the best indicator.
Work on vocalisation in North America suggest that, in that continent alone, there are eight or nine populations of Red Crossbill with different calls, which rarely if ever interbreed. These forms also vary in terms of bill size and structure, and specialise on the seed cones of different species of conifer. Few ornithologists seem inclined to give these forms species status at present.
Some large-billed, pine-feeding populations currently assigned to this species in the Mediterranean area may possibly be better referred to either Parrot Crossbill or alternatively to new species in their own right, but as yet, research into them is still at a very early stage. These include Balearic Crossbill L. curvirostra balearica and North African Crossbill L. curvirostra poliogyna, feeding primarily on Aleppo Pine (Pinus halepensis); Cyprus Crossbill L. curvirostra guillemardi, feeding primarily on European black pine (Pinus nigra); and an as-yet unidentified crossbill with a Parrot Crossbill-size bill feeding primarily on Bosnian Pine (Pinus heldreichii) in the Balkans. These populations also differ on plumage, with the Balearic, North African and Cyprus races 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.
Common Crossbill diversity
Distinct Eurasian Common Crossbill populations:
- Balearic Crossbill, Loxia curvirostra balearica
- Associated with Aleppo Pine Pinus halepensis
- North African Crossbill, Loxia c. poliogyna
- Associated with Aleppo Pine Pinus halepensis
- Corsican Crossbill, Loxia c. corsicana
- Associated with European Black Pine, Pinus nigra
- Cyprus Crossbill, Loxia c. guillemardi
- Associated with European Black Pine, Pinus nigra
- Crimean Crossbill, Loxia c. mariae
- Associated with European Black Pine, Pinus nigra?
- Luzon Crossbill, Loxia c. luzoniensis
- Associated with Khasi Pine, Pinus kesiya
- Annam Crossbill, Loxia c. meridionalis
- Associated with Khasi Pine, Pinus kesiya
As with Parrot and Scottish Crossbills, all of the above are fairly sedentary forms associated with hard-coned Pinus species. The following are more associated with the softer cones of spruce and larch:
- Altai Crossbill, Loxia c. altaiensis
- Tien Shan Crossbill, Loxia c. tianschanica
- Associated with Schrenk's Spruce Picea shrenkiana
- Himalayan Crossbill, Loxia c. himalayensis
- Associated with Himalayan Hemlock Tsuga dumosa
- Japanese Crossbill, Loxia c. japonica
North American Red Crossbill subspecies list based on biometrics:
- Newfoundland Crossbill, Loxia c. percna Possibly extinct
- Lesser Crossbill, Loxia c. minor
- Sitka Crossbill, Loxia c. sitkensis
- Loxia c. neogaea
- Rocky Mountain Crossbill, Loxia c. benti
- Sierra Crossbill, Loxia c. grinnelli
- Bendire Crossbill, Loxia c. bendirei
- Mexican Crossbill, Loxia c. stricklandi
- Central American Crossbill, Loxia c. mesamericana
- South Hills Crossbill (no scientific name[verification needed])
Jeff Groth's classification of North American Red Crossbill forms based on call-types:
- Type 1, corresponds with Loxia c. neogaea
- Recorded on Tsuga species, Picea glauca, Pinus strobus
- Type 2, corresponds with Loxia c. benti/grinnelli/bendirei
- Recorded on Rocky Mountains Ponderosa Pine Pinus ponderosa scopulorum in the west and in various Pinus species in the east
- Type 3, corresponds with Loxia c. sitkensis and Loxia c. minor
- Recorded on Western Hemlock Tsuga heterophylla
- Type 4, corresponds with Loxia c. neogaea
- Recorded on Douglas Fir Pseudotsuga menziesii
- Type 5, corresponds with Loxia c. benti/grinnelli/bendirei
- Recorded on Lodgepole Pine Pinus contorta latifolia
- Type 6, corresponds with Loxia c. stricklandi
- Uses Pine species in Section Trifoliae
- Type 7, corresponds with Loxia c. benti/grinnelli/bendirei
- In terms of diet this type is possibly a generalist
- Type 8, corresponds with Loxia c. percna
- Uses Black Spruce Picea mariana
- Type 9, corresponds with South Hills Crossbill
- Isolated population of Lodgepole Pine Pinus contorta latifolia
Summers' list of European Common Crossbill forms (with Parrot & Scottish) based on Flight/Excitement calls:
- 1A, corresponds with "British" Crossbill
- 1B, corresponds with "Parakeet" Crossbill
- 2B, corresponds with "Wandering" Crossbill
- 2D, corresponds with Parrot Crossbill Loxia pytyopsittacus
- 3C, corresponds with Scottish Crossbill Loxia scotica
- 3D, corresponds with Balearic Crossbill
- 3E, corresponds with North African Crossbill
- 4E, corresponds with "Glip" Crossbill
- 5D, corresponds with Cyprus Crossbill
"The Sound Approach's" classification of European Common Crossbill types based on call-types:;
- "Wandering" Crossbill (Type A - flight call "Keep")
- "Bohemian" Crossbill (Type B - flight call "Weet")
- "Glip" Crossbill (Type C - flight call "Glip")
- "Phantom" Crossbill (Type D - flight call "Jip")
- "British" Crossbill (Type E - flight call "Chip")
- "Scarce" Crossbill (Type F - flight call "Trip")
- "Parakeet" Crossbill (Type X - flight call "Cheep")
