Red Crossbill

Loxia curvirostra

Order:
Passeriformes
Family:
Fringillidae
Sections

Distribution, Migration, and Habitat

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Figure 1. Distribution of the Red Crossbill in North America.

Based on knowledge of major crossbill audio collections, conifer distributions, published literature, and documented records. Core Zone of Occurrence (solid dark purple) represents the area where key conifers are found and where birds can regularly be found utilizing those key conifers during most typical years -- Breeding is common in numbers the majority of years. Secondary Zone of Occurrence (solid light purple) represents area where lesser numbers of birds can be found many years with some regularity -- Small numbers of breeding birds present most years. Primary Zone of Irruption (solid dark blue, and it also sometime includes a light dashed purple line to represent area where some call types are known to irrupt to, and nest, occasionally in small numbers) represents area where birds commonly move to when cone crops on key conifers fail in their core zones of occurrence – these areas often harbor conifer species most similar to those found in core zones, and in some years upon arrival, if cone crops are good on appropriate conifers, they can nest in small numbers. Secondary Zone of Irruption (solid light blue) represents area where birds move to only when there’s widespread cone failures on many conifers they typical use in core zones -- nesting is rare. Solid light yellow represents tertiary zone of irruption where movement is uncommon and breeding rare and local, and it only pertains to Type 2. Dashed Blue represents area of irruptive migration. Solid light purple dots represent known local breeding.

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eBird range map for Red Crossbill

Generated from eBird observations (Year-Round, 1900-present)

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Figure 5. Co-occurrence of Red Crossbill Call Types.

Although multiple call types can be found in many regions of North America, multiple call types are regularly found in the same region only in the western United States and British Columbia. The greatest diversities and abundances of crossbills are found in the extensive and diverse conifer forests of the Pacific Northwest. Map compiled by Craig Benkman and Matthew A. Young.

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Figure 6. Map of Type 1 Appalachian Red Crossbill.

Core Zone of Occurrence (solid dark purple) represents the area where key conifers are found and where birds can regularly be found utilizing those key conifers during most typical years -- Breeding is common in numbers the majority of years. Secondary Zone of Occurrence (solid light purple) represents area where lesser numbers of birds can be found many years with some regularity -- Small numbers of breeding birds present most years. Primary Zone of Irruption (solid dark blue, and it also sometimes includes a light dashed purple line) represents area where birds commonly move to when cone crops on key conifers fail in their core zones of occurrence – these areas often harbor conifer species most similar to those found in core zones, and in some years upon arrival, if cone crops are good on appropriate conifers, they can nest in small numbers. Secondary Zone of Irruption (solid light blue) represents area where birds move to only when there’s widespread cone failures on many conifers they typical use in core zones -- nesting is rare. Dashed Blue represents area of irruptive migration. Solid light purple dots represent known isolated breeding, and solid black dots represent vagrant records. Type 1 is the call type most associated with eastern North America. Map compiled by Matthew A. Young.

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Figure 7. Map of Type 2 Ponderosa Pine Red Crossbill.

Core Zone of Occurrence (solid dark purple) represents the area where key conifers are found and where birds can regularly be found utilizing those key conifers during most typical years -- Breeding is common in numbers the majority of years. Secondary Zone of Occurrence (solid light purple) represents area where lesser numbers of birds can be found many years with some regularity -- Small numbers of breeding birds present most years. Primary Zone of Irruption (solid dark blue) represents area where birds commonly move to when cone crops fail on key conifers in their core zones of occurrence – these areas often harbor conifer species most similar to those found in core zones, and in some years upon arrival, if cone crops are good on appropriate conifers, they can nest in small numbers. Secondary Zone of Irruption (solid light blue) represents area where birds move to only when there’s massive widespread cone failures on many conifers they typical use in core zones -- nesting is rare. Solid light yellow represents tertiary zone of irruption where movement is uncommon and breeding quite rare, and it only pertains to Type 2. Dashed Blue represents area of irruptive migration. Solid light purple dots represent known isolated breeding. Type 2 is very likely the most widespread call type. Map compiled by Matthew A. Young.

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Figure 8. Map of Type 3 Western Hemlock Red Crossbill.

Core Zone of Occurrence (solid dark purple) represents the area where key conifers are found and where birds can regularly be found utilizing those key conifers during most typical years -- Breeding is common in numbers the majority of years. Secondary Zone of Occurrence (solid light purple) represents area where lesser numbers of birds can be found many years with some regularity -- Small numbers of breeding birds present most years. Primary Zone of Irruption (solid dark blue, and it also sometime includes a light dashed purple line) represents area where birds commonly move to when cone crops on key conifers fail in their core zones of occurrence – these areas often harbor conifer species most similar to those found in core zones, and in some years upon arrival, if cone crops are good on appropriate conifers, they can nest in small numbers. Secondary Zone of Irruption (solid light blue) represents area where birds move to only when there’s massive widespread cone failures on many conifers they typical use in core zones -- nesting is quite rare. Dashed blue line represents area of irruptive migration. Solid black dots represent vagrant records. Type 3 make regular movements to the northeast and northern Rockies every few years. Map compiled by Matthew A. Young.

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Figure 9. Map of Type 4 Douglas Fir Red Crossbill.

Core Zone of Occurrence (solid dark purple) represents the area where key conifers are found and where birds can regularly be found utilizing those key conifers during most typical years -- Breeding is common in numbers the majority of years. Secondary Zone of Occurrence (solid light purple) represents area where lesser numbers of birds can be found many years with some regularity -- Small numbers of breeding birds present most years. Primary Zone of Irruption (solid dark blue, and it also sometimes includes a light dashed purple line) represents area where birds commonly move to when cone crops on key conifers fail in their core zones of occurrence – these areas often harbor conifer species most similar to those found in core zones, and in some years upon arrival, if cone crops are good on appropriate conifers, they can nest in small numbers. Secondary Zone of Irruption (solid light blue) represents area where birds move to only when there’s massive widespread cone failures on many conifers they typical use in core zones -- nesting is quite rare. Dashed blue line represents area of irruptive migration. Solid light purple dots represent known isolated breeding, and solid black dots represent vagrant records. Type 4 make regular movements every few years to the Northern Rockies. Map compiled by Matthew A. Young.

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Figure 10. Map of Type 5 Lodgepole Pine Red Crossbill.

Core Zone of Occurrence (solid dark purple) represents the area where key conifers are found and where birds can regularly be found utilizing those key conifers during most typical years -- Breeding is common in numbers the majority of years. Secondary Zone of Occurrence (solid light purple) represents area where lesser numbers of birds can be found many years with some regularity -- Small numbers of breeding birds present most years. Primary Zone of Irruption (solid dark blue) represents area where birds commonly move to when cone crops fail on key conifers in their core zones of occurrence – these areas often harbor conifer species most similar to those found in core zones, and in some years upon arrival, if cone crops are good on appropriate conifers, they can nest in small numbers. Secondary Zone of Irruption (solid light blue) represents area where birds move to only when there’s massive widespread cone failures on many conifers they typical use in core zones -- nesting is quite rare. Solid black dots represent vagrant records. Type 5 appears to form residency more readily, and irruptive migration is thought to be uncommon. Map compiled by Matthew A. Young.

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Figure 11. Map of Type 6 Sierra Madre Red Crossbill.

Core Zone of Occurrence (solid dark purple) represents the area where key conifers are found and where birds can regularly be found utilizing those key conifers during most typical years -- Breeding is common in numbers the majority of years. Primary Zone of Irruption (solid dark blue) represents area where birds commonly move to when cone crops fail on key conifers in their core zones of occurrence – these areas often harbor conifer species most similar to those found in core zones, and in some years upon arrival, if cone crops are good on appropriate conifers, they can nest in small numbers. Solid black dots represent vagrant records. Appears to be resident across much of its range in Mexico, but more data is still needed. Map compiled by Matthew A. Young.

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Figure 12. Map of Type 7 Enigmatic Red Crossbill.

Core Zone of Occurrence (solid dark purple) represents the area where key conifers are found and where birds can be found utilizing those key conifers during most typical years -- Breeding is common in numbers the majority of years. Secondary Zone of Occurrence (solid light purple) represents area where lesser numbers of birds can be found many years with some regularity -- Small numbers of breeding birds present most years. Primary Zone of Irruption (solid dark blue) represents area where birds commonly move to when cone crops fail on key conifers in their core zones of occurrence – these areas often harbor conifer species most similar to those found in core zones, and in some years upon arrival, if cone crops are good on appropriate conifers, they can nest in small numbers. Secondary Zone of Irruption (solid light blue) represents area where birds move to only when there’s massive widespread cone failures on many conifers they typical use in core zones -- nesting is quite rare. Dashed blue line represents area of irruptive migration. Solid black dots represent vagrant records. Initially thought to be a western call type, but more data (map is provisional) is still needed on this call type since its status remains "enigmatic." Map compiled by Matthew A. Young.

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Figure 13. Map of Type 8 Newfoundland Red Crossbill.

Core Zone of Occurrence (solid dark purple) represents the area where key conifers are found and where birds can regularly be found utilizing those key conifers during most typical years -- Breeding is common in numbers the majority of years. Secondary Zone of Occurrence (solid light purple) represents area where lesser numbers of birds can be found many years with some regularity -- Small numbers of breeding birds present most years. This threatened call type (ssp. percna) has recently been discovered in small numbers on Anticosti Island, Quebec. Red Crossbill recordings are needed from coastal areas of northern Nova Scotia and New Brunswick to determine whether it occurs there. Map compiled by Matthew A. Young.

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Figure 14. Map of Cassia Crossbill (formerly Type 9).

Core Zone of Occurrence (solid dark purple) represents the area where key conifers are found and where birds can regularly be found utilizing those key conifers during most typical years -- Breeding is common in numbers the majority of years. Type 9 was raised to species status (Cassia Crossbill) in 2017. Map compiled by Craig Benkman.

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Figure 15. Map of Type 10 Sitka Spruce Red Crossbill.

Core Zone of Occurrence (solid dark purple) represents the area where key conifers are found and where birds can regularly be found utilizing those key conifers during most typical years -- Breeding is common in numbers the majority of years. Secondary Zone of Occurrence (solid light purple) represents area where lesser numbers of birds can be found many years with some regularity -- Small numbers of breeding birds present most years. Primary Zone of Irruption (solid dark blue) represents area where birds commonly move to when cone crops fail on key conifers in their core zones of occurrence – these areas often harbor conifer species most similar to those found in core zones, and in some years upon arrival, if cone crops are good on appropriate conifers, they can nest in small numbers. Secondary Zone of Irruption (solid light blue) represents area where birds move to only when there’s massive widespread cone failures on many conifers they typical use in core zones -- nesting is quite rare. More data is needed to determine how irruptive this call type is, map is provisional in the east. Map compiled by Matthew A. Young.

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Figure 16. Map of Type 11 Central American Red Crossbill.

Based on knowledge of major crossbill audio collections, published literature, documented records and cone-ripening phenologies. Core Zone of Occurrence (solid dark purple) represents the area where key conifers are found and where birds can regularly be found utilizing those key conifers during most typical years -- Breeding is common in numbers the majority of years. Primary Zone of Irruption (solid dark blue) represents area where birds commonly move to when cone crops fail on key conifers in their core zones of occurrence – these areas often harbor conifer species most similar to those found in core zones, and in some years upon arrival, if cone crops are good on appropriate conifers, they can nest in small numbers. More data is needed on this call type. Map compiled by Matthew A. Young.

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Figure 2. Annual cycle of breeding, migration, and molt for Red Crossbill.

Data from literature on North American Red Crossbills. Thick lines show peak activity; thin lines, off-peak.

Distribution in the Americas

Breeding Range

Figure 1. In North America, breeds in coniferous and mixed coniferous–deciduous forests from Alaska to eastern Canada, southward to limits of spruce (Picea), pines (Pinus), douglas-fir (Pseudotsuga menziesii), and hemlocks (Tsuga). At the species level, breeding range extends from south-coastal and southeastern Alaska (west to the base of the Alaska Peninsula and Kodiak Island) (71), throughout British Columbia, including Queen Charlotte and Vancouver islands (76), western and southern Yukon (77), southwestern Northwest Territories (78), western and southern Alberta (79), southwestern Saskatchewan (80), southern Ontario (except maybe southernmost areas; 81), southern Quebec (82), Newfoundland (now rare; 83, 84, 66), and throughout the Maritime Provinces (85).

Across the United States, breeds in coastal and montane coniferous forests of Oregon (86) and Washington (87). In California, south along coast range to Sonoma County, south through Sierra Nevada to Tulare County and in the San Gabriel, San Bernardino and San Jacinto mountains (88), and in the Panamint and White mountains east of the Sierra (89, 90, CWB). In Nevada: western (Carson Range), central (Desatoya Mountains), northeastern (Ruby and Jarbridge mountains), southern (Sheep Range), and eastern (Schell Creek and Snake ranges) regions (91, 92). Mountainous coniferous forests of Idaho, Montana (93), Wyoming (94), Colorado, (95), Arizona (96), and New Mexico (97), the Guadalupe Mountains, and probably Davis Mountains of western Texas (31, 98), extreme western South Dakota (Black Hills and Harding County; 99), extreme northwestern Nebraska (100), northeastern Minnesota (101), northern Wisconsin (102), Upper Peninsula of Michigan (103), northern and central New York (104), northern Vermont (105), southern and central New Hampshire (106, 107), eastern Massachusetts, and eastern Maine (108). Breeds more locally the Appalachian Mountains from southern New York through northern Pennsylvania, western Virginia, eastern West Virginia, eastern Tennessee, and western North Carolina (109). Breeds sporadically outside of this area (e.g., New Jersey; [110]) when conditions suitable for breeding exist, and small populations appear to occasionally exist in Arkansas and Alabama. Has very rarely bred in the U.S. as far south as Texas, Mississippi (111), western Tennessee (112), and Arkansas (113), where there was even recent nesting of Type 1 and Type 2 (MAY, A. Deshwal, P. Panwar, unpublished data); Red Crossbills often breed in such areas after major eruptions.

In Middle America, breeds at elevations from 900 to 3,500 m in north-central Baja California Norte, in the interior and on adjacent slopes of mainland Mexico irregularly from western Chihuahua, southern Tamaulipas, and central Guatemala (114), south to Mountain Pine Ridge in central Belize (115), highlands of western Honduras (116, 117), and northern highlands and Mosquitia in Nicaragua (118).

Distribution of Call Types

All maps are based on knowledge of major Red Crossbill audio collections, conifer distributions and phenologies, published literature, and documented records. Many of the call types appear to have the following areas they occupy throughout their life: (a) Core Zone of Occurrence (see Figure 1), which represents the area where birds are most consistently found and where key conifers occur (i.e., conifers that tend to be regular seed producers that consistently holds some seeds in cones through winter and into spring [e.g., especially pines like lodgepole pine]; see 4, 119)—breeding is common in the majority of years, (b) Secondary Zone of Occurrence, which represents an area where lesser numbers of birds occur with some regularity—small numbers of breeding birds are present in the majority of years, (c) Primary Zone of Irruption, which represents an area where birds regularly move to when Red Crossbill populations are large and cone crops fail in their core zone of occurrence—these areas often harbor conifer species most similar to those found in core zones, and in some years upon arrival, if cone crops are good on appropriate conifers, they can nest in small numbers, and (d) Secondary Zone of Irruption, which represents an area where crossbills move to only when there’s massive widespread cone failures on many conifers they typical use in core zones—breeding is rare, and largely confined to Type 2. They also appear to have corridors where irruptive migration is more common (see Figure 1 and Maps).

Alaska and Canada. Type 3 (Figure 8) is the most common call type in Alaska, with Type 1 (Figure 6) and Type 10 (Figure 15) found much less regularly. In western Canada, especially in British Columbia, Type 3 and Type 4 (Figure 9) are most common in coastal areas, whereas inland in the Canadian Rockies, Type 2 (Figure 7) and Type 5 (Figure 10) predominate with lesser numbers of Type 3 and Type 4 in the southern part of the area. In eastern Canada, “eastern Type 10” is the most common type, especially in the southern Maritimes west to Algonquin Provincial Park, Ontario (120), but recent studies suggest that many eastern “Type 10s” are possibly Type 7 (13). More study is needed for Type 7 (Figure 12 is provisional). Small numbers of Type 1 and Type 2 (largely "unkinked" Type 2; 9) can also be found in southeastern Canada, and approximately every 2–5 yr large numbers of Type 3 move west-to-east sometimes swamping out the other “quasi-resident” call types in southeastern Canada. Type 4 has very rarely been recorded in southeastern Canada. Type 8 (Figure 13) is largely endemic to Newfoundland (15), but has recently been found in Anticosti Island (66).

United States. Similar for what is written for Canada above, much of the same applies in that along the coastal areas of the Pacific Northwest U.S, types 3, 4, and 10 are most common, especially for Type 10 in northern California and southern Oregon (6). In interior mountainous regions of the U.S., Type 2 (largely "kinked" Type 2; 9) and Type 5 again predominate, but Type 4 appears to occur in small numbers every couple years at least to the central Rockies and sometimes even to southern Arizona where it can occur with the similar sounding Type 6 (Figure 11). Type 3 is relatively rare in the central Rockies, and even rarer to Arizona except during the largest irruptions. Type 7 appears to be quite rare in the West, and Type 10 is yet to be even found in interior mountainous regions. Formerly known as Type 9 (Figure 14), Cassia Crossbill (Figure 14) occurs in 2 isolated mountain ranges (South Hills and Albion Mountains) in southern Idaho. In the eastern U.S., "unkinked" Type 2 and “eastern” 10 are the most common types in the Great Lakes and Northeast regions. Type 4 was confirmed breeding in the jack pine–red pine (Pinus banksianaP. resinosa) areas of northern Wisconsin in 2018 (see Ryan Brady audio recordings), but it's unknown if Type 5, a vagrant to the East (121), has ever bred in the East. In the northeastern U.S, Type 10 (which is possibly Type 7) is by far the most common breeding type from the Adirondacks through the White Mountains of New Hampshire into north-central and coastal Maine. Small numbers of Type 1 and Type 2 also breed throughout much of the mountainous east (including apparently northwestern Arkansas), with Type 1 more commonly occurring (than Type 2) in the southern Appalachians of the Virginias to the Carolinas and Alabama. Approximately every 2–5 yr, large numbers of Type 3 move west-to-east into the northeastern States, and breeding occurs with some regularity in the Northeast.

Middle America. In Central America, primarily only 2 types are known, Type 6 (Figure 11) through the Sierra Madre from the U.S. border south to Honduras, and Type 11 (Figure 16) from the highlands of Guatemala, Honduras, Belize, Nicaragua, and El Salvador north to southern Guerrero, Mexico. Type 2 also occurs in Baja California of Mexico and across the Arizona and New Mexico borders into the northern parts of Mexico.

Nonbreeding Range

Figure 1. Found year-round throughout breeding range but may wander considerable distances from regular breeding areas when not breeding (typically during winter months). Major irruptions may involve thousands of birds, and irruptions are more common in types 2, 3, and 4. Wandering birds have been recorded as far south as southern Florida (122) and southern Baja California Norte (114), but most wanderers in eastern North America are likely to be encountered in the northern U.S. (to sea level). In Honduras, wandering birds may enter broadleaf forests during nonbreeding season (116), and in California nonbreeders may invade a variety of areas, from deserts to urban gardens (90).

Distribution Outside the Americas

British Isles and Scandinavia, across Asia in taiga and mountain ranges, through Siberia and Transbaikalia to Japan, and Kamchatka (123, 47, 32). L. c. curvirostra breeds regularly in European mountains, including the Alps, Pyrenees, and in other forested areas (32). Distinctive forms occur in the Himalayas, Japan, Vietnam, Philippines, several large islands of the Mediterranean (Cyprus, Mallorca), and the Atlas Mountains of northern Africa. Irruptions from Siberia sometimes bring huge numbers to western Europe, with around 50 major irruptions occurring from 1800–1970 (47); see also 124 and 42. Other crossbill species occur in Scandinavia and western Russia, including the Parrot Crossbill, and in Scotland, both the Scottish Crossbill and Parrot Crossbill (125, 73, 32).

Nature of Migration

Wanders nomadically within and sometimes beyond conifer forests. Movements generally coincide with the depletion of seed crops especially between fall and spring, and with the maturation of new crops in summer (126, 47, 14, 19). Perhaps the most dispersive of all songbirds, with Red Crossbills in Europe moving up to 3,000 km between natal and breeding sites, and between breeding sites (127); banding records are more limited in North America with only 8 records of movement beyond 500 km and a maximum movement of 1,955 km (128); see also 54. Red Crossbill irruptions in western Europe after moderate cone crops (when only the least proficient or subordinate birds should emigrate) consisted of about 72% juveniles; after small cone crops, irruptions consisted of about 30% juveniles; adult females outnumbered adult males over all invasions (126).

Red Crossbill invasions of types 3, 4, and “kinked” Type 2 in eastern North America coincided with poor cone crops in the West that followed large western cone crops that would have resulted in population buildup (16). For example, following cone crop failures of western hemlock in the coastal forests of Alaska and the Pacific Northwest, some to thousands of Type 3 apparently fly across the continent and settle in the eastern hemlock forests in the Great Lakes and Northeast (1, 13), which would represent distances of 4,000 km or more. Such movements by Type 3 occur about every 2–5 yr (e.g., 2006, 2009, 2012, 2017; eBird data). Type 2 often move from the Rocky Mountains into the Great Plains regions, and Type 4 move out of the Pacific Northwest into the Intermountain West and occasionally Great Lakes. Some crossbills are resident in response to stable seed supplies (129), including especially the closely related Cassia Crossbill (130). Indeed, some individuals of nomadic Type 2 and Type 5 become resident (recaptured annually in the same net for up to 4 yr) upon moving into the pine forests occupied by the Cassia Crossbill, highlighting the facultative responsiveness of crossbills to seed availability (128).

Timing and Routes of Migration

Red Crossbill makes 1 to 3 movements annually, as in White-winged Crossbill (52), tracking the phenology of conifer seed development and shedding from cones: seeds ripen over summer and most North American conifers begin shedding their seeds from the cones by early autumn. When seed crops are large, sufficient seed to sustain crossbills is often held in the cones through winter and into spring and even early summer. In most years, warm conditions in May and June generally cause the last seeds to be shed from cones, and crossbills then search for developing seed crops on which to feed (131, 51). Because the regional scale over which large seed crops are produced varies from year to year (16), distances traveled to locate large cone crops presumably varies similarly. Movements occur in September–November if seed crops are not large and/or weather conditions (warm and windy) lead to rapid seed shedding. Movements may occur in winter and spring also in response to seed shedding/depletion. In North America, large flights are often seen May–June and especially October–January (132, eBird data); in Ohio, large irruptions first detected by late August, smaller movements in mid-October (133); similar pattern in Missouri (134). During irruption years in the Midwest (e.g., 1921–1922, 1931–1932, 1940–1941, 1954–1955, 1972–1973; Peterjohn [133]), large numbers (flocks of about 30–50, and up to 200 birds) are seen, most leaving by late May.

In Europe, there is one main movement in summer when crossbills search for developing cone crops, especially Norway spruce, with fall and spring movements occurring less regularly than in North America because spruce and pine cones remain closed until spring (47, 32).

Migratory Behavior

Makes long flights by day (47). Migrating birds show restless, excited behavior, as in White-winged Crossbill (135). Captive Type 3 individuals were more active in June coinciding with the period of regular movement (51). No evidence of nocturnal migration (51).

Control and Physiology of Migration

Food availability is the primary proximate driver of movements (47, 14), which is supported by Koenig and Knops (16) who reported that the combination of large population size and small cone crops cause Red Crossbill irruptions in eastern North America. The mechanism underlying irruptive movements may be regulated, in part, by an adaptive stress response that is responsive to food and social cues. Activity levels and stress hormones (corticosterone) increase with food restriction in captive Type 3, and are further heightened when individuals in adjacent cages are similarly food restricted (136, 137). Some types may rely at least in part on predictive cues such as endogenous rhythms or the seasonal change in photoperiod to prepare for or time the more consistent spring nomadic movement. Captive Type 3 show evidence of endogenous cycles of elevated fat and activity during late spring and early summer when crossbills normally move (51); see Newton (126, 47) and Summers et al. (138) for fat accumulation in May and June prior to movements; the relatively sedentary Red Crossbill in the Pyrenees, Spain, have low levels of fat year-round (139). The seasonal responses of nomadic crossbills are likely adaptive because they prepare individuals to move when such movements become necessary (51). However, endogenous cycles and changes in day length alone are likely insufficient to cause movements because, for example, individuals of (nomadic) Type 2 and Type 5 become resident for multiple years upon encountering stable seed supplies (128). More research is needed to better describe migratory mechanisms in crossbills, particularly as it relates to variation in resource availability and different call types.

Habitat in Breeding Range

Breeds in mature conifer forests, but generally avoids dense forests; occurs wherever large cone crops have been produced by spruce (Picea spp.), douglas-fir, western hemlock, eastern hemlock (Tsuga canadensis), western larch (Larix occidentalis) and many species of pine (see Distribution). As in White-winged Crossbill (52), a critical factor influencing breeding is conifer seed availability, and its changes over time in relationship to the changing seasonal requirements for successful reproduction (17), except perhaps in autumn (18, 19) presumably due to the demands for timely molt and perhaps reduced survivorship of young fledged (see Breeding: Phenology). Red Crossbill breeds in the same white spruce and Engelmann spruce forests as White-winged Crossbill when both are foraging on late-summer and early-autumn cone crops (14, 52). Multiple call types can be found breeding in the same forests (58, CWB, MAY; T. Spahr, T. Hahn and C. Porter, personal communications). Crossbills drink daily and the availability of water could limit their occurrence in areas without much snow or standing water (32).

Habitat Associations of Call Types

Most call types appear to associate primarily with one or a few conifer species, with bill size (especially depth) positively associated with cone size and hardness (2, 3, 4, 140). However, all call types potentially forage on a diversity of conifers, especially those having cones that are smaller and softer (and thus the seeds are more accessible) than those commonly used; one notable exception is Type 3, which forages on larger, harder cones after those cones open and seeds are readily accessible.

Starting with the smallest billed call type and progressing to the largest, Type 3 is closely associated with the small, thin-scaled cones of western hemlock, especially closer to the coast where humid conditions reclose cones enhancing seed retention (4); regularly feeds on Sitka spruce after its cones open (CWB, T. Hahn, personal communication). Foraging experiments demonstrate that Type 3's average bill depth and width of the groove in the horny palate where seeds are secured while husking closely approximate the optimal for foraging on seeds in western hemlock cones implying evolutionary specialization (4). During large but occasional eruptions to the Great Lakes and Northeast, Type 3 associates with eastern hemlock (131, 54, 141) and red spruce (Picea rubens; MAY), the former has very similar cones and seeds to western hemlock. Type 10 is strongly associated with Sitka spruce along the Pacific coast, and is mostly restricted to such forests south of Canada perhaps because of more regular seed production (6) or because of competition with Type 3, which commonly utilizes Sitka spruce to the north. Irwin (6) spent > 10,000 hours observing Type 10 near the coast in northern California and found that Type 10 foraged on Sitka spruce seeds to the near exclusion of other foods. In support of its specialization on Sitka spruce, Type 10's husking groove width matches that predicted for foraging on Sitka spruce and its relatively large bill depth compared to Type 3 is expected for efficient foraging on the larger cones of Sitka spruce as compared to hemlock (6; see 4). "Type 10" has also been reported from the Great Lakes region and the Northeast where it seems to regularly utilize red pine and eastern white pine, but also a diversity of other conifers such as jack pine and pitch pine (Pinus rigida) (13). However, it is possible that many of these “Type 10” are instead the larger-billed Type 7 (13) discussed below. The next largest types are the similarly sized Type 1 and Type 4 (3). Type 1 occurs most commonly in the Appalachians where Groth (2) observed it foraging mostly on eastern white pine (P. strobus), whereas C. S. Adkisson (142) observed it foraging on red spruce. What conifer or conifers it is most strongly associated with, especially in late winter and spring when seed is most limiting, requires further study; it is unlikely to be eastern white pine because it usually sheds nearly all of its seeds by late winter (14). It is possible that types in the East (e.g., types 1 and “eastern” 10) more regularly use a strategy of shifting to different conifer species throughout the year rather than being specialized on a single conifer species like many types in the West, given that the East has high conifer diversity, but low density (141). Type 4 is most common in the Pacific Northwest where it is usually found foraging on douglas-fir (Pseudotsuga m. menziesii). Foraging experiments indicate evolutionary specialization (i.e., morphological) of Type 4 on douglas-fir (4). Type 5 is most closely associated with Rocky Mountain lodgepole pine, and seems most abundant in forests where the frequency of serotinous cones is highest. Serotinous cones remain closed for years and even decades until heated by for example fire, but, as cones weather, gaps form between the scales allowing access to seeds year-round (130, 143). Type 5 forages on Engelmann spruce, which is often associated with lodgepole pine at higher elevations in the Rocky Mountains, douglas-fir (Pseudotsuga m. glauca), and blue spruce (Picea pungens) when these conifers produce large cone crops (C. Porter, T. Hahn, J. Cornelius, personal communication). However, its bill structure matches the predicted optimum for foraging on lodgepole pine and is much larger than the optimum for foraging on Engelmann spruce implying that even extensive foraging on the thin, soft scaled cones of Engelmann spruce (as well as douglas-fir and blue spruce) has had little impact on bill size evolution (7). Type 7 is the least known of the call types. It was first described from east of the Cascades (3), but many of those appear to be a better match for Type 2 (i.e., ones with U-shaped spectrograms). The U-shaped spectrograms first described in Groth (3) appear to be a variant of “kinked” Type 2, which is not surprising given the lack of genetic differences between this variant of Type 7 and Type 2 (10). Groth’s (3) Type 7 (recording no. jM498), however, is a perfect match to the eastern birds currently listed as Type 10, and therefore this type appears to be much more common in the Northeast and occasionally into the Great Lakes (13). Type 2 is most common in the ponderosa pine (especially P. ponderosa scopulorum) forests in the Rocky Mountain region and the Columbia Basin, and this association is consistent with a bill structure that approximates the optimum for both extracting (8) and husking seeds from ponderosa pine (4). Type 2 is also the most common call type in the Sierra Nevada where it generally associates with lodgepole pine (Pinus contorta murrayana), which produces non-serotinous cones that are much softer than those in the Rocky Mountains. Type 2 occurs much less commonly in ponderosa pine in the Sierra Nevada presumably because of its relatively large cones and seeds that are difficult for Type 2 to access (4,144). In eastern North America, Type 2 (mostly "unkinked" Type 2) has bred in association with other pines including jack pine (MAY), red pine, eastern white pine, and table mountain pine (Pinus pungens) (2, 3, 17). The Central American form (Type 11, L. c. mesamericana) is most common in the highlands in association with egg-cone pine (P. oocarpa) (116; J. van Dort, personal communication), which has serotinous cones and for the reasons above discussed for Rocky Mountain lodgepole pine likely provides a year-round seed source. Type 8 (L. c. percna) associates primarily with Newfoundland black spruce (Picea mariana; produces semi-serotinous cones), which in the absence of red squirrel (Tamiasciurus hudsonicus) has evolved enhanced seed defenses favoring a large bill in an apparent coevolutionary arms race (48). The largest billed New World crossbill, Type 6 (L. c. stricklandi, 1), occurs in southwestern New Mexico, southeastern Arizona, and south in the Sierra Madre de Occidental to southern Mexico (1, 3). Its range encompasses the greatest diversity of pine species in the world (145). The occurrence of only one call type in such a pine-rich area is an enigma; although only certain Madrean pines (i.e., Apache pine [Pinus engelmannii], Chihuahua pine [P. leiophylla], Arizona pine [P. arizonica]) are likely important food trees, and these might not be sufficiently divergent and stable to favor multiple call types, but this requires study.

Habitat in the Overwintering Range

No true migration to winter habitats.

Historical Changes to the Distribution

Apparently no major changes in distribution in recent history, although regional changes in abundance have occurred. Most notably, Red Crossbill was formerly common in Newfoundland, but is now rare (83, 48, 84). Increases in call type reporting to eBird should help identify future changes. See Demography and Populations: Population Status for details on population trends.

Fossil History

Red Crossbill fossils have been reported from the Late Pleistocene of Carpinteria, California; Coconino County, Arizona; and Eddy County, New Mexico (146). Fossil crossbills from > 9,000 years ago that were found on Abaco Island, Bahamas (147) may include Red Crossbills (148).

Recommended Citation

Benkman, C. W. and M. A. Young (2019). Red Crossbill (Loxia curvirostra), version 2.0. In The Birds of North America (P. G. Rodewald, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bna.redcro.02