Loxia curvirostra

Linnaeus, 1758

Red Crossbill

G5Secure Found in 287 roadless areas NatureServe Explorer →
G5SecureGlobal Rank
Least concernIUCN
MediumThreat Impact
Identity
Unique IDELEMENT_GLOBAL.2.1009908
Element CodeABPBY05050
Record TypeSPECIES
ClassificationSpecies
Classification StatusStandard
Name CategoryVertebrate Animal
IUCNLeast concern
Endemicoccurs (regularly, as a native taxon) in multiple nations
KingdomAnimalia
PhylumCraniata
ClassAves
OrderPasseriformes
FamilyFringillidae
GenusLoxia
COSEWICPS:T
Other Common Names
Bec-croisé des sapins (FR) Picotuerto Rojo (ES) red crossbill (EN)
Concept Reference
American Ornithologists' Union (AOU). Chesser, R.T., K.J. Burns, C. Cicero, J.L. Dunn, A.W. Kratter, I.J. Lovette, P.C. Rasmussen, J.V. Remsen, Jr., J.D. Rising, D.F. Stotz, and K. Winker. 2017. Fifty-eighth Supplement to the American Ornithologists' Union Check-list of North American Birds. The Auk 134:751-773.
Taxonomic Comments
Loxia sinesciuris was formerly considered conspecific with L. curvirostra, but treated as a separate species on the basis of high levels of premating reproductive isolation (Smith and Benkman 2007, Benkman et al. 2009), despite regular and likely long-term sympatric breeding of multiple call types of Red Crossbill, and genomic differences (Parchman et al. 2016) (AOU 2017).
Conservation Status
Rank MethodExpertise without calculation
Review Date2016-04-09
Change Date1996-12-04
Edition Date2009-03-24
Edition AuthorsHammerson, G.
Threat ImpactMedium
Range Extent>2,500,000 square km (greater than 1,000,000 square miles)
Number of Occurrences> 300
Rank Reasons
Widespread in North America and Eurasia; large population size; many occurrences, though these are variable in location; apparently stable or slowly declining overall in North America but trends are difficult to determine; taxonomic status is uncertain, and status and rank could change significantly if ongoing research confirms the suspicion that L. curvirostra consists of multiple species.
Range Extent Comments
As traditionally defined, this species occurs widely in Eurasia and North America. In North America it is resident from southeastern Alaska eastward across boreal Canada to Newfoundland and Nova Scotia, and south in the west to northern Baja California and through the mountains to Nicaragua, and south in the east to Great Lakes region, southern Appalachian Mountains, New York, and New England. (Adkisson 1996, AOU 1998). In the nonbreeding season this species disperses irregularly throughout much of the remainder of the contiguous United States. The several types or species of red crossbills are highly nomadic and may shift breeding ranges by as much as a thousand miles between one breeding season and the next (Groth 1993).
Occurrences Comments
This species is represented by a large number of occurrences (subpopulations), but crossbills are not permanent residents of any particular occurrence.
Threat Impact Comments
Decline of the Newfoundland population (subspecies percna) evidently has been due at least in part to competition from the introduced red squirrel (Benkman 1993).

Local declines and increases reflect variations in local conifer cone crops; widespread deforestation or low cone availability results in emigration of crossbills to other areas. Net reduction in total area of mature forest (or in overall cone availability) presumably would result in an overall decline in the crossbill population, so recent forestry practices and widespread regional tree mortality due to insect outbreaks likely are detrimental to crossbills, at least temporarily.
Ecology & Habitat

Habitat

Coniferous and mixed coniferous-deciduous forests; also pine savanna and pine-oak habitat. In migration and winter may also occur in deciduous forest, and more open scrubby areas.

Nests in conifers, 1.5-25 m above ground, toward outer end of branch (Terres 1980).

Ecology

Forms flocks when not breeding; does not maintain a feeding territory. Pairs may forage more than 500 meters from nest (Bailey 1953, Nethersole-Thompson 1975).

Reproduction

Breeding season is variable, depends in part on food supply. Clutch size is 3-4, sometimes 5. Incubation, by female (fed by male), lasts about 12-14 days. Young leave nest about 17 days after hatching (Terres 1980), may be fed for two more weeks.
Terrestrial Habitats
Forest - ConiferForest - MixedWoodland - ConiferWoodland - MixedSavanna
Other Nations (2)
CanadaN5
ProvinceRankNative
OntarioS5Yes
Prince Edward IslandS1B,SUMYes
Northwest TerritoriesS5Yes
British ColumbiaS5Yes
SaskatchewanS4B,S5N,S5MYes
QuebecS4Yes
New BrunswickS3Yes
AlbertaS5Yes
ManitobaS3Yes
Island of NewfoundlandS1Yes
Yukon TerritoryS5Yes
Nova ScotiaS3Yes
United StatesN5
ProvinceRankNative
OhioSNRNYes
KentuckySNAYes
Navajo NationS3Yes
AlabamaS1BYes
UtahS3Yes
WashingtonS4BYes
North CarolinaS2Yes
WisconsinSUB,S2NYes
OregonS4Yes
District of ColumbiaS1NYes
South CarolinaS2Yes
CaliforniaSNRYes
PennsylvaniaS1B,S4N,S3MYes
KansasSNAYes
South DakotaS4B,S3NYes
WyomingS5B,S5NYes
West VirginiaS2B,S2NYes
TexasS3Yes
New MexicoS4B,S4NYes
GeorgiaSUYes
New YorkS2Yes
VermontS1B,S2NYes
North DakotaSNAYes
New JerseySUMYes
MassachusettsS1B,S4NYes
MaineS3B,S3NYes
MichiganS4Yes
TennesseeS1B,S2NYes
MissouriSNAYes
OklahomaS1NYes
MontanaS5Yes
NevadaS4Yes
ArkansasS3NYes
ConnecticutSNAYes
VirginiaS1Yes
IowaS2NYes
IndianaS1NYes
MinnesotaSNRB,SNRNYes
ColoradoS5Yes
MississippiS1BYes
ArizonaS4Yes
AlaskaS4Yes
NebraskaS4Yes
New HampshireSNAYes
IdahoS4Yes
IllinoisS1Yes
Roadless Areas (287)
Alaska (12)
AreaForestAcres
Bering LakeChugach National Forest965,076
Copper River WetlandsChugach National Forest85,972
Game CreekTongass National Forest54,469
GravinaTongass National Forest37,381
Kenai LakeChugach National Forest213,172
Kenai MountainsChugach National Forest306,600
North BaranofTongass National Forest314,089
RedoubtTongass National Forest68,347
RevillaTongass National Forest29,298
Roaded DonutChugach National Forest968
Sheridan GlacierChugach National Forest224,683
Sitka UrbanTongass National Forest112,003
Arizona (7)
AreaForestAcres
BoulderTonto National Forest40,359
Butterfly Roadless AreaCoronado National Forest42,296
ChiricahuaCoronado National Forest76,876
HellsgateTonto National Forest6,171
PinalenoCoronado National Forest130,920
Red PointKaibab National Forest7,139
TumacacoriCoronado National Forest44,594
California (52)
AreaForestAcres
Bell MeadowStanislaus National Forest7,968
Benton RangeInyo National Forest9,637
Birch CreekInyo National Forest28,816
Black ButteLos Padres National Forest5,116
Black CanyonInyo National Forest32,421
Boundary Peak (CA)Inyo National Forest210,884
Cactus Springs BSan Bernardino National Forest3,106
Caples CreekEldorado National Forest17,854
Carson - IcebergStanislaus National Forest56,430
Chips CreekLassen National Forest29,089
Coyote SoutheastInyo National Forest53,159
DardanellesEldorado National Forest8,110
DomeStanislaus National Forest11,085
Domeland Add.Sequoia National Forest3,046
EagleStanislaus National Forest16,116
Excelsior (CA)Inyo National Forest45,607
Glass MountainInyo National Forest52,867
Granite PeakSan Bernardino National Forest450
Hall Natural AreaInyo National Forest5,236
Heart LakeLassen National Forest9,349
Hoover - Mt.olsenHumboldt-Toiyabe National Forest624
Hoover - NorthHumboldt-Toiyabe National Forest1,574
Hoover - Virginia LksHumboldt-Toiyabe National Forest5,050
Horse Mdw.Inyo National Forest5,687
Kings RiverSierra National Forest52,999
LavasModoc National Forest25,864
Log Cabin SaddlebagInyo National Forest15,165
Mill PeakSan Bernardino National Forest7,884
Mt. HoffmanModoc National Forest9,780
Mt. OlsenInyo National Forest2,161
Mt. Shasta BShasta-Trinity National Forest2,809
North Fork Middle Fork American RiverTahoe National Forest11,245
PyramidEldorado National Forest24,347
Pyramid Peak BSan Bernardino National Forest7,194
Raymond PeakEldorado National Forest2,518
Raymond PeakStanislaus National Forest3,646
Red MountainAngeles National Forest8,034
Rock Creek WestInyo National Forest3,626
Sheep MountainAngeles National Forest21,098
SherwinInyo National Forest3,140
Soldier CanyonInyo National Forest40,589
South SierraInyo National Forest41,853
South SierraSequoia National Forest8,008
Tioga LakeInyo National Forest829
Tragedy - Elephants BackEldorado National Forest20,866
Trail LakeLassen National Forest1,124
WaterhouseStanislaus National Forest4,394
WattersonInyo National Forest6,922
West GirardShasta-Trinity National Forest37,516
Wheeler RidgeInyo National Forest15,744
Wonoga Pk.Inyo National Forest11,272
WoodpeckerSequoia National Forest11,936
Colorado (7)
AreaForestAcres
Comanche Peak Adjacent AreaArapaho & Roosevelt NFs44,158
Dome PeakRoutt NF35,716
HermosaSan Juan NF148,103
Long ParkRoutt NF42,100
Red TableWhite River NF39,122
San MiguelSan Juan NF64,263
Storm PeakSan Juan NF57,617
Georgia (3)
AreaForestAcres
Joe GapChattahoochee National Forest5,321
Patterson GapChattahoochee National Forest1,186
Pink KnobChattahoochee National Forest12,127
Idaho (7)
AreaForestAcres
HoodooNez Perce-Clearwater National Forest153,868
NeedlesPayette National Forest131,279
PalisadesCaribou-Targhee National Forest122,002
Peace RockBoise National Forest191,734
Pioneer MountainsSawtooth National Forest119,563
Pioneer MountainsSalmon-Challis National Forest172,460
SeceshPayette National Forest248,088
Michigan (1)
AreaForestAcres
FibreHiawatha National Forest7,432
Minnesota (1)
AreaForestAcres
Hegman LakesSuperior National Forest675
Montana (32)
AreaForestAcres
Allen Peak #185Kootenai National Forest29,638
Anderson MountainBeaverhead-Deerlodge National Forest31,501
Bear - Marshall - Scapegoat - SwanHelena National Forest51,360
Bear - Marshall - Scapegoat - SwanLolo National Forest118,485
Bear - Marshall - Scapegoat - SwanLewis and Clark National Forest344,022
Big Snowy Mountains WsaLewis and Clark National Forest88,003
Bmss Ra 1485Flathead National Forest334,275
BridgerGallatin National Forest45,059
Buckhorn Ridge (MT)Kootenai National Forest34,716
Cabinet Face East #671Kootenai National Forest50,326
CataractKootenai National Forest25,446
Cube Iron - SilcoxLolo National Forest36,998
Freezeout MountainBeaverhead-Deerlodge National Forest97,305
Gold Hill West #176Kootenai National Forest15,079
HoodooLolo National Forest105,162
Jerico MountainHelena National Forest8,445
Lazyman GulchHelena National Forest11,614
Line Creek PlateauCuster National Forest24,825
Mt. Gmt Area HCuster National Forest1,335
North AbsarokaCuster National Forest21,063
North AbsarokaGallatin National Forest159,075
North Big HoleBeaverhead-Deerlodge National Forest52,227
Patricks Knob - North CutoffLolo National Forest16,970
Red Lodge Creek HellroaringCuster National Forest17,210
Scotchman Peaks (MT)Kootenai National Forest53,909
Selway - Bitterroot (01067)Bitterroot National Forest114,953
Sheep Mountain - StatelineLolo National Forest37,844
South Siegel - South CutoffLolo National Forest13,474
Sundance RidgeLolo National Forest7,558
Ten Lakes #683Kootenai National Forest48,545
West Big HoleBeaverhead-Deerlodge National Forest133,563
Willard Estelle #173Kootenai National Forest3,714
Nevada (6)
AreaForestAcres
Angel Peak NorthHumboldt-Toiyabe National Forest12,577
Arc Dome - MahoganyHumboldt-Toiyabe National Forest4,208
Mystic (NV)Humboldt-Toiyabe National Forest5,644
Rose - Davis Mdw.Humboldt-Toiyabe National Forest2,361
Rose - GalenaHumboldt-Toiyabe National Forest3,711
Rose - Whites CanyonHumboldt-Toiyabe National Forest2,568
New Hampshire (4)
AreaForestAcres
Cherry MountainWhite Mountain National Forest8,766
PemigewassetWhite Mountain National Forest32,255
Pemigewasset ExtWhite Mountain National Forest15,840
Sandwich RangeWhite Mountain National Forest16,797
New Mexico (19)
AreaForestAcres
Bear MountainSanta Fe National Forest1,387
Black CanyonSanta Fe National Forest1,922
El InviernoSanta Fe National Forest29,927
GallinasSanta Fe National Forest13,208
Holy GhostSanta Fe National Forest2,352
Juan de Gabaldon GrantSanta Fe National Forest8,023
LemitasSanta Fe National Forest8,129
Little TesuqueSanta Fe National Forest815
Meadow CreekGila National Forest34,167
Mt. TaylorCibola National Forest6,355
Nichols ReservoirSanta Fe National Forest1,518
PecosCarson National Forest13,436
Pecos WS RiverSanta Fe National Forest5,396
RendijaSanta Fe National Forest2,176
Ryan HillCibola National Forest34,201
San Pedro ParksSanta Fe National Forest5,824
Tesuque CreekSanta Fe National Forest810
Thompson PeakSanta Fe National Forest33,001
West Face Sacramento MountainsLincoln National Forest41,176
North Carolina (7)
AreaForestAcres
Bald MountainPisgah National Forest11,085
Balsam ConePisgah National Forest10,591
BearwallowPisgah National Forest4,113
Jarrett CreekPisgah National Forest7,485
Laurel MountainPisgah National Forest5,683
Middle Prong AdditionPisgah National Forest1,852
Overflow CreekNantahala National Forest3,379
Oregon (37)
AreaForestAcres
BearwallowsDeschutes National Forest7,317
Bend WatershedDeschutes National Forest14,829
EagleMt. Hood National Forest16,841
Echo MountainWillamette National Forest8,098
Greenhorn MountainMalheur National Forest15,936
Greenhorn Mtn.Umatilla National Forest11,191
Hebo 1aSiuslaw National Forest13,930
HellholeUmatilla National Forest65,679
Horseshoe RidgeUmatilla National Forest5,996
Jaussaud CorralUmatilla National Forest5,535
Joseph CanyonWallowa-Whitman National Forest24,288
Jumpoff JoeUmatilla National Forest5,516
LakeMt. Hood National Forest1,327
Lake ForkWallowa-Whitman National Forest21,936
Little SheepWallowa-Whitman National Forest5,238
LookingglassUmatilla National Forest4,859
Maiden PeakDeschutes National Forest26,432
Maiden PeakWillamette National Forest9,627
Mt. JeffersonDeschutes National Forest2,282
Mt. BaileyUmpqua National Forest18,401
Mt. Hood AdditionsMt. Hood National Forest13,061
North PaulinaDeschutes National Forest19,670
OlallieMt. Hood National Forest7,607
ReservoirWallowa-Whitman National Forest13,641
SherwoodUmpqua National Forest2,449
Sky Lakes AWinema National Forest3,940
South PaulinaDeschutes National Forest9,074
TahkenitchSiuslaw National Forest5,799
TenmileSiuslaw National Forest10,818
Twin LakesMt. Hood National Forest6,055
Twin MountainWallowa-Whitman National Forest58,533
Umpqua SpitSiuslaw National Forest2,090
Upper Catherine CreekWallowa-Whitman National Forest6,446
Waldo - FujiWillamette National Forest15,273
Walla Walla RiverUmatilla National Forest34,416
West - South BachelorDeschutes National Forest25,994
WoahinkSiuslaw National Forest5,309
Pennsylvania (2)
AreaForestAcres
Allegheny FrontAllegheny National Forest7,430
Hearts ContentAllegheny National Forest221
South Dakota (2)
AreaForestAcres
Cheyenne RiverBuffalo Gap National Grassland7,572
Red ShirtBuffalo Gap National Grassland17,007
Utah (23)
AreaForestAcres
0419020Ashley National Forest355,684
418028Uinta National Forest34,002
418029Uinta National Forest15,673
418040Uinta National Forest1,702
Boulder Mtn. / Boulder Top / Deer LakeDixie National Forest110,690
CottonwoodDixie National Forest6,754
FishhookDixie National Forest12,959
HancockDixie National Forest9,809
Happy ValleyDixie National Forest14,458
High Uintas (UT)Wasatch-Cache National Forest102,398
LakesWasatch-Cache National Forest121,967
Lava BedsDixie National Forest14,944
Lone Peak ContiguousWasatch-Cache National Forest874
Marysvale PeakFishlake National Forest22,624
Mt. NaomiWasatch-Cache National Forest41,922
Mt. OlympusWasatch-Cache National Forest9,982
Pine Valley MountainsDixie National Forest57,673
Signal PeakFishlake National Forest30,889
Stansbury MountainsWasatch-Cache National Forest39,696
Temple PeakWasatch-Cache National Forest24,081
Twin PeaksWasatch-Cache National Forest6,157
WellsvilleWasatch-Cache National Forest1,717
White PineWasatch-Cache National Forest1,942
Vermont (2)
AreaForestAcres
Bread LoafGreen Mountain and Finger Lakes National Forests1,768
Griffith Lake 09084Green Mountain and Finger Lakes National Forests1,833
Virginia (11)
AreaForestAcres
Bear CreekJefferson National Forest18,274
Brush MountainJefferson National Forest6,002
Crawford MountainGeorge Washington National Forest9,892
Gum RunGeorge Washington National Forest12,620
Little RiverGeorge Washington National Forest27,292
North MountainJefferson National Forest8,377
Oak KnobGeorge Washington National Forest10,882
Peters Mountain Addition BJefferson National Forest2,909
Ramseys Draft AdditionGeorge Washington National Forest12,781
Seng MountainJefferson National Forest6,428
SkidmoreGeorge Washington National Forest5,641
Washington (20)
AreaForestAcres
Alpine Lakes Adj.Wenatchee National Forest57,104
Blue SlideWenatchee National Forest17,505
ChelanWenatchee National Forest74,650
Dixon MountainGifford Pinchot National Forest6,339
EntiatWenatchee National Forest72,617
Goat Rocks AdjWenatchee National Forest6,108
Grassy TopIdaho Panhandle National Forests13,485
Harvey CreekColville National Forest10,140
Jefferson RidgeOlympic National Forest6,512
Jupiter RidgeOlympic National Forest10,148
LightningOlympic National Forest7,179
Mill Creek Watershed (WA)Umatilla National Forest16,747
Mt. Baker MaMt Baker-Snoqualmie National Forest24,847
Mt. BaldyOlympic National Forest3,557
Norse PeakWenatchee National Forest10,169
Rock CreekWenatchee National Forest32,239
SawtoothOkanogan National Forest122,194
South QuinaultOlympic National Forest11,081
SpanglerUmatilla National Forest5,936
TaneumWenatchee National Forest26,140
West Virginia (8)
AreaForestAcres
Canaan LoopMonongahela National Forest7,867
Cranberry AdditionMonongahela National Forest11,123
Cranberry Glades Botanical AreaMonongahela National Forest785
Dolly Sods Roaring PlainMonongahela National Forest13,392
Dry River (WV)George Washington National Forest7,331
Falls Of Hills CreekMonongahela National Forest6,925
Mcgowan MountainMonongahela National Forest10,504
Seneca CreekMonongahela National Forest22,287
Wisconsin (1)
AreaForestAcres
09166 - East TorchChequamegon-Nicolet National Forest4,647
Wyoming (23)
AreaForestAcres
Beartooth Proposed WildernessShoshone National Forest16,837
Canyon CreekShoshone National Forest7,530
Doyle CreekBighorn National Forest6,542
French CreekMedicine Bow-Routt National Forest5,928
Grayback RidgeBridger-Teton National Forest295,113
Gros Ventre MountainsBridger-Teton National Forest106,418
Hazelton PeaksBighorn National Forest10,029
Laramie PeakMedicine Bow-Routt National Forest28,608
Libby FlatsMedicine Bow-Routt National Forest11,107
Middle ForkShoshone National Forest51,772
Monument RidgeBridger-Teton National Forest17,720
PalisadesTarghee National Forest1,121
Phillips RidgeBridger-Teton National Forest10,108
Piney CreekBighorn National Forest22,240
Snowy RangeMedicine Bow-Routt National Forest29,660
South Beartooth HighwayShoshone National Forest105,570
Spread Creek - Gros Ventre RiverBridger-Teton National Forest166,097
Sulphur CreekShoshone National Forest30,221
Teton Corridor TrailheadsBridger-Teton National Forest286
West Slope TetonsTarghee National Forest47,448
West Slope WindsBridger-Teton National Forest143,252
Wilderness Study AreaTarghee National Forest51,961
Windy MountainShoshone National Forest31,283
References (29)
  1. Adkisson, C.S. 1996. Red Crossbill; The Birds of North America. Vol. 7, No. 256. American Orinithologists' Union. The Academy of Natural Sciences of Philadelphia.
  2. American Ornithologists' Union (AOU). 1983. Check-list of North American Birds, 6th edition. Allen Press, Inc., Lawrence, Kansas. 877 pp.
  3. American Ornithologists' Union (AOU). 1998. Check-list of North American birds. Seventh edition. American Ornithologists' Union, Washington, D.C. [as modified by subsequent supplements and corrections published in <i>The Auk</i>]. Also available online: http://www.aou.org/.
  4. American Ornithologists' Union (AOU). Chesser, R.T., K.J. Burns, C. Cicero, J.L. Dunn, A.W. Kratter, I.J. Lovette, P.C. Rasmussen, J.V. Remsen, Jr., J.D. Rising, D.F. Stotz, and K. Winker. 2017. Fifty-eighth Supplement to the American Ornithologists' Union Check-list of North American Birds. The Auk 134:751-773.
  5. Bailey, A. M., R. J. Niedrach, and A. L. Baily. 1953. The Red Crossbills of Colorado. Museum Pictorial No. 9, Denver Museum of Natural History, Denver, Colorado.
  6. Benkman, C. W. 1989. On the evolution and ecology of island populations of crossbills. Evolution 43:1324-1330.
  7. Benkman, C. W. 1990. Intake rates and the timing of crossbill reproduction. Auk 107:376-386.
  8. Benkman, C. W. 1993a. Logging, conifers, and the conservation of crossbills. Conservation Biology 7(3):473-479.
  9. Benkman, C. W. 1993b. The evolution, ecology, and decline of the red crossbill in Newfoundland. Am. Birds 47(2):225-229.
  10. Benkman, C. W. 1993c. Adaptation to single resources and the evolution of crossbill (LOXIA) diversity. Ecological Monographs 63:305-325.
  11. BirdLife International. 2004b. Threatened birds of the world 2004. CD ROM. BirdLife International, Cambridge, UK.
  12. Byrd, M. A., and D. W. Johnston. 1991. Birds. Pages 477-537 in K. Terwilliger, coordinator. Virginia's endangered species: proceedings of a symposium. McDonald and Woodward Publ. Co., Blacksburg, Virginia.
  13. DeBenedictus, P. A. 1995. Red crossbills, one through eight. Birding 27(6):494-501.
  14. Dickerman, R. W. 1987. The "old northeastern" subspecies of red crossbill. Am. Birds 41:188-194.
  15. Griscom, L. 1937. A monographic study of the red crossbill. Proc. Boston Soc. Nat. Hist. 41:(5). 133 pp.
  16. Groth, J. G. 1988. Resolution of cryptic species in Appalachian red crossbills. Condor 90:745-760.
  17. Groth, J. G. 1993a. Call matching and positive assortative mating in red crossbills. Auk 110:398-401.
  18. Groth, J. G. 1993b. Evolutionary differentiation in morphology, vocalizations, and allozymes among nomadic sibling species in the North American red crossbill (LOXIA CURVIROSTRA) complex. Univ. California Publ. Zool. 127. 143 pp.
  19. Harrison, C. 1978. A Field Guide to the Nests, Eggs and Nestlings of North American Birds. Collins, Cleveland, Ohio.
  20. Howell, S. N. G., and S. Webb. 1995. A guide to the birds of Mexico and northern Central America. Oxford University Press, Oxford, UK.
  21. Knox, A.G. 1990. The sympatric breeding of common and Scottish crossbills Loxia curvirostra and L. scotia and the evolution of crossbills. Ibis 132:454-466.
  22. Nethersole-Thompson, D. 1975. Pine Crossbills: a Scottish contribution. T. and A. D. Poyser, Berkhamsted, U.K.
  23. Parker III, T. A., D. F. Stotz, and J. W. Fitzpatrick. 1996. Ecological and distributional databases for neotropical birds. The University of Chicago Press, Chicago.
  24. Peterson, R.T. 1980b. A field guide to the birds of eastern and central North America. Houghton Mifflin Company, Boston.
  25. Peterson, R.T. 1990b. A field guide to western birds. Houghton Mifflin Company, Boston.
  26. Poole, A. F. and F. B. Gill. 1992. The birds of North America. The American Ornithologists' Union, Washington, D.C. and The Academy of Natural Sciences, Philadelphia, PA.
  27. Rich, T. D., C. J. Beardmore, H. Berlanga, P. J. Blancher, M.S.W. Bradstreet, G. S. Butcher, D. W. Demarest, E. H. Dunn, W. C. Hunter, E. E. Iñigo-Elias, A. M. Martell, A. O. Panjabi, D. N. Pashley, K. V. Rosenberg, C. M. Rustay, J. S. Wendt, T. C. Will. 2004. Partners in Flight North American landbird conservation plan. Cornell Lab of Ornithology. Ithaca, NY. Online. Available: <u><http://www.partnersinflight.org/cont_plan/></u>
  28. Terres, J. K. 1980. The Audubon Society encyclopedia of North American birds. Alfred A. Knopf, New York.
  29. Zook, J. L. 2002. Distribution maps of the birds of Nicaragua, Costa Rica, and Panama. Unpublished.