Red Crossbil has intrigued and puzzled ornithologists since Linnaeus first gave the species a scientific name in 1758. Until the late 20th century, Red Crossbill included birds from both the Old and New worlds. In both areas Red Crossbills vary in overall size and bill shape, but, particularly in North America, attempts to assign subspecies names to birds of different sizes was frustrated by their overlapping ranges. Ornithologists now view the taxa in North America as consisting of 9 species each with different vocalizations and feeding preferences for specific cone-bearing trees. Flocks of crossbills wander widely until they find an adequate supply of cones to enable them to breed. Until the calls of live birds can be correlated with existing museum specimens whose measurements overlap, grouping of individuals into these new species will not be possible (Adkisson 1996, Am. Ornithol. Union 1998)
DISTRIBUTION. During the 1987-1992 field work for the TBBA project, observers found confirmed breeding evidence for Red Crossbill in the Guadalupe Mountains and probable breeding in the Davis Mountains of Trans-Pecos Texas. At times of poor cone crops, these nomadic birds may appear outside their normal breeding range (Adkisson 1996, Lockwood and Freeman 2004).
Outside Texas Red Crossbills breed from southeast Alaska across Canada to Newfoundland and south through the conifer forests of North America, Mexico and Guatemala.
SEASONAL OCCURRENCE. Red Crossbills move in nomadic flocks as they search for their preferred conifer cones. When they find an adequate cone supply they stop and breed any time from December to September. (Adkisson 1996). When fresh cones are not available they substitute other food sources, including old pine cones or young, green true fir cones, still full of sticky pitch (RCT).
BREEDING HABITAT. Red Crossbills breed in coniferous forest, in Trans-Pecos Texas primarily ponderosa pine around 2400m (8000 ft; Oberholser 1974). In Arizona with montane habitats similar to those of the Trans-Pecos mountains, About 88% of Red Crossbill nests found in the Arizona Breeding Bird Atlas fieldwork were in various habitats in which ponderosa pine was a major component (Corman 2005).
The nest is saddled in a thick tuft of needles, far out from the trunk on a tree branch, 1.5-24 m (5-80 ft) above the ground. The loosely arranged, bulky structure is built of twigs, rootlets, decayed wood, lichens and bark strips and lined with moss, fine grass, feathers and fur. The outside diameter is 11.5-14 cm (4.5-5.5 in), height 7.5-9 cm (3-3.5 in), inside diameter 5-6.5 cm (2-2.5 in), cup depth 3.2-4.5 cm (1.3-1.8 in). The nest is indistinguishable from that of White-winged Crossbill (Loxia leucoptera).
The female usually lays 4 (range 3-5_smooth, slightly glossy, bluish or greenish white eggs (see Harrison  for photo of markings). The female incubates the eggs for 12-14 (or even 16) days, her olive-green plumage blends well with conifer foliage. Her mate feeds her on the nest, allowing long periods of incubation. Young birds leave the nest 16-25, or even 35) days after hatching. Brood parasitism has not been reported (Harrison 1979, Adkisson 1996). The long incubation and nestling periods may refer to winter nests
STATUS. Lockwood and Freeman (2004) characterize Red Crossbill as rare and irregular in the highest Trans-Pecos mountains. The Breeding Bird Survey does not sample this species in Texas.. Data from 445 routes (40 km [25 m,i] long) on which Red Crossbills were detected across the United States and Canada produce a 95% confidence interval (There is a 95% chance that the actual population trend will be between these two numbers.) of -2.3 to +0.3% (Sauer et al. 2005). This rate of decline suggests that Red Crossbills will continue to wander into Texas for years to come although their status as breeders will be a function of cone crops in the Guadalupe and Davis mountains. Text by Robert C. Tweit (2005)
Adkisson, C. S. 1996. Red Crossbill (Loxia curvirostra). In The birds of North America, No. 256 (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA.
Corman, T. E. 2005.Red Crossbill (Loxia curvirostra). In Arizona breeding bird atlas.p p. 580-581 (T. E. Corman and C. Wise-Gervais, eds.), University of New Mexico Press, Albuquerque.
Harrison, H. H. 1979. A field guide to western birds’ nests. Houghton Mifflin, Boston, MA.
Lockwood, M. W. and B. Freeman. 2004. The TOS handbook of Texas birds. Texas A&M University Press, College Station.
Oberholser, H. C. 1974. The bird life of Texas, Vol. 2. University of Texas Press, Austin.
Sauer, J. R., J. E. Hines, and J. Fallon. 2005. The North American Breeding Bird Survey, results and analysis 1966-2004. Version 2005.1. USGS Patuxent Wildlife Research Center, Laurel MD (Web site, http://www.mbr-pwrc.usgs.gov/bbs).