Loxia curvirostra

Geographic Range

Red crossbills are found throughout the northern hemisphere. They are not migratory, but wander widely outside of the breeding season. Occasional irruptions may involve thousands of birds traveling to areas outside of their normal range. In the Americas, red crossbills are found in northern boreal and high altitude coniferous forests from coastal Alaska throughout much of Canada to the maritime provinces and south to northern Minnesota, Wisconsin, Michigan, New York, New Hampshire, Vermont, and Maine. They are found in appropriate habitat throughout the Sierra, Rocky Mountain, and Sierra Madre mountain ranges, as well as smaller mountain ranges in Baja California, Honduras, Nicaragua, Belize, and the Mexican volcanic belt. Small, disjunct breeding populations are found in the Appalachian Mountains and occasional breeding populations are found in appropriate habitat outside of their typical range. In the Palearctic, red crossbills are found from the British Isles across northern Europe, Russia, and Asia to the Kamchatka Peninsula and Japan. They are also found in appropriate habitat in mountain ranges, including the Alps, Pyrenees, Himalayas, Vietnam, the Philippines, and into the Atlas Mountains of northern Africa. They co-occur with other Loxia species in Scotland ( Loxia scotica ), Scandinavia and western Russia ( Loxia pytyopsittacus ), and North America ( Loxia leucoptera ).

• Biogeographic Regions
• nearctic nearctic
  • native native
• palearctic palearctic
  • native native

• Other Geographic Terms
• holarctic holarctic

Habitat

Red crossbills are found almost exclusively in mature, coniferous forests, including spruce ( Picea ), fir ( Abies ), hemlock ( Tsuga ), and pine ( Pinus ) forests. They can also be found in mixed decidous-coniferous forests, provided there are ample supplies of conifer seeds to eat. Specific "call types" of red crossbills are associated with 1 or more conifer species. For example, two large-billed types of red crossbills in western North America are found closely associated with the large cones of Engelmann's spruce ( Picea engelmanni ), ponderosa pine ( Pinus ponderosa ), and table mountain pine ( Pinus pungens ). Another, eastern type associates mainly with Newfoundland black spruce ( Picea mariana ). Small-billed red crossbills associate with conifers with smaller cones, such as hemlocks ( Tsuga ) and Douglas-fir ( Pseudotsuga ). This close association between call types and conifer species has led to the description of many subspecies and speculation about strong selection of food types on bill-shape and subsequent reproductive isolation through vocalizations (call types). However, a study of mitochondrial DNA showed no evidence of reproductive isolation among subspecies or call types. Morphological differences among populations specialized to particular conifer species may be the result of rapid local adaptations.

• Habitat Regions
• temperate temperate
• terrestrial terrestrial

• Terrestrial Biomes
• forest forest

Physical Description

Red crossbills are medium-sized finches with distinctive, curved mandibles that are crossed at their tips. Males are slightly larger than females (males: 23.8 to 45.4 g, females: 23.7 to 42.4 g). Males are a deep red color, sometimes reddish yellow, with dark brown flight and tail feathers. Females are olive to gray or greenish yellow on the breast and rump with dark brown flight and tail feathers. Immature birds are overall streaked with brown on a lighter background. The tail is notched. Red crossbills don't undergo any seasonal changes in plumage. They are easily distinguished from other species by their crossed bills, except for other Loxia species. In North America, white-winged crossbills ( Loxia leucoptera ) are distinguished by their white wing bars.

Red crossbills show a striking amount of geographic variation in body size and bill size and shape, despite the fact that populations regularly co-occur and that all populations range widely outside of the breeding season. Morphologies are also associated with distinctive call types. Some researchers have proposed up to 8 North American cryptic species based on call type and associated morphology. Similar levels of variation and tight association of call types and foraging morphology is observed in the Palearctic. Some evidence of reproductive isolation has been reported in the Palearctic, but mitochondrial DNA sequence data does not support the notion of reproductive isolation, instead finding that mitochondrial haplotypes mixed at continental scales.

Basal metabolic rate of captive red crossbills was estimated at 19% higher than expected for their body size.

• Other Physical Features
• endothermic endothermic
• homoiothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• male larger
• sexes colored or patterned differently
• male more colorful

Reproduction

Red crossbills are monogamous and seem to stay in pairs throughout the year. Pairs use identical flight calls and seem to remain together throughout the year, although there is no direct evidence that year-round pairs are also mates in breeding season. Males sing from perches and make display flights to attract females. Males are aggressive towards other males during the breeding season. Courtship involves feeding the female and billing (grabbing each other by the bill). Males then accompany females constantly after courtship and during the period of egg-laying, presumably to prevent extra-pair copulations.

• Mating System
• monogamous monogamous

Many aspects of breeding phenology and behavior are strongly influenced by the availability of food. Throughout their range, red crossbills may be found breeding in almost every month, although local populations breed seasonally. Some populations, given enough conifer seed resources, can breed for up to 9 months out of the year. In North America eggs have been observed from December to September. Mated pairs select a nest site, usually an interior, densely covered branch of a conifer tree from 2 to 20 meters above ground. Males may contribute nesting materials, but females build the nest. Nests are constructed of conifer twigs lined with grasses, lichen, conifer needs, shredded bark, and feathers. Females lay 3 eggs typically, 1 each day, with incubation starting at the last egg laid, unless the weather is cold. Females incubate eggs for 12 to 16 days and brood nearly continuously for 5 days after hatching. Hatchlings go into torpor during brief absences of the female from the nest. Both hatching and fledging may be delayed by cold weather or lack of food. Young fledge at 15 to 25 days after hatching, depending on the availability of food. After fledging, the young follow their parents around (or only the male parent if the female lays a second clutch) and continue to beg for food and practice obtaining seeds from conifer cones. Parents sometimes feed their young for up to 33 days after they have fledged. Young red crossbills may become sexually mature even before they have taken on their adult plumage, as early as 100 days after hatching.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• oviparous oviparous

Young red crossbills hatch in an altricial state, with no down. Females incubate and brood the young and males help to defend small foraging territories, provide some courtship food to the female, and feed hatchlings and fledglings until they become proficient at extracting conifer seeds from cones.

• Parental Investment
• altricial altricial
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • male
    • female
• pre-weaning/fledging
  • provisioning
    • male
    • female
  • protecting
    • male
    • female
• pre-independence
  • provisioning
    • male
    • female

Lifespan/Longevity

Information on lifespan in the wild is not reported in the literature. Captive red crossbills can live up to 8 years in the wild. Females may suffer higher predation rates because of the extended periods of time they spend on the nest.

Behavior

Red crossbills are social, flocking birds. They don't migrate but do range widely in search of good conifer seed crops outside of the breeding season. There is no evidence of natal philopatry. They are well-adapted to cold weather and seem to move in response to cone crop availability. Mass movements of red crossbill populations most often occur in fall, when conifer cones ripen. These movements can involve thousands of birds and can result in invasions of new regions by wandering populations of crossbills. Red crossbills are strong, fast fliers.

• Key Behaviors
• flies
• diurnal diurnal
• motile motile
• nomadic nomadic
• social social

Home Range

There is no evidence of territoriality in red crossbills and no home ranges. Small territories may be defended during the breeding season, but more research is needed. These birds are largely nomadic.

Communication and Perception

Red crossbills are divided into discrete "call types" that correspond to bill morphologies that allow them to specialize on the conifer seeds of particular conifer species. Young red crossbills of all call types make similar sounds during the nestling and fledgling stages. By the time they reach independence, however, they are using the specific call type of their parents. Mated pairs imitate each other to produce identical flight calls to remain in contact with each other. Flight calls are described as a "chip chip chip." Males sing from perches near their nest, songs are described as a buzzing "whit-whit" or "zzzt zzzt," although these songs also vary among call types. Other vocalizations used include alarm or distress calls, and excitement, threat, chitter, or courtship calls.

• Communication Channels
• acoustic acoustic

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

Red crossbills feed exclusively on conifer seeds. Populations, or call types, may have specialized bill morphologies that make them most efficient at extracting the seeds from cones of particular conifer species. Red crossbills travel in feeding flocks that help individuals take best advantage of locally variable conifer seed crops. Flocking is thought to help these crossbills avoid predation while also assessing the best areas for foraging. Red crossbill calls and calling rates transmit information on the availability of food. Flying birds join foraging flocks when the foraging birds are calling. However, call rate increases among foraging birds as they spend more time feeding and, perhaps, begin to have less success in finding food. As the call rate reaches a crescendo, the flock departs to look for another foraging opportunity. The calls of foraging birds do not attract flying groups of another call type, however, which is consistent with their specialization on different conifer species.

Red crossbills feed mainly on conifer cones still attached to trees, although they will also hold unattached cones in their feet. They use their peculiar mandibles to bite between cone scales so that, as they bite, the lower mandible opens the scale and exposes the conifer seed. In particularly tough cones they may have to bite several times or twist with their head before they can reach the conifer seed with their tongue. Their "crossed" mandibles are essential for this task and allow them to exploit a niche not otherwise exploited among seed-eating birds. Once they expose a conifer seed, they remove the seed coat with their tongue and mandible and either swallow small seeds whole or crush larger seeds. Red crossbills take grit or sand into their crop to help with processing their seed diet.

• Primary Diet
• herbivore herbivore
  • granivore granivore

• Plant Foods
• seeds, grains, and nuts

Predation

Observed North American predators include sharp-shinned hawks ( Accipiter striatus ) on adults and Tamiasciurus species, gray jays ( Perisoreus canadensis ), and Steller's jays ( Cyanocitta stelleri ) on eggs and nestlings. Likely predators include other raptors that specialize on birds: Cooper's hawks ( Accipiter cooperi ), merlins ( Falco columbarius ), peregrine falcons ( Falco peregrinus ), and northern shrikes ( Lanius excubitor ). American kestrels ( Falco sparverius , sharp-shinned hawks ( Accipiter striatus ), and northern pygmy owls ( Glaucidium gnoma ) have all been observed attacking red crossbill decoys. Eurasian predators are likely to be similar: bird specialist raptors, corvids , and squirrels.

Ecosystem Roles

Red crossbills are important seed predators of conifers across their range and regional populations are highly specialized to extract seeds of particular conifer species. They are parasitized by biting lice ( Mallophaga ).

Economic Importance for Humans: Positive

Red crossbills are interesting and integral parts of the coniferous, forested habitats in which they live. They are a fascinating example of extreme specialization to a food type and subsequent rapid morphological adaptation.

• Positive Impacts
• research and education

Economic Importance for Humans: Negative

Red crossbills do not adversely affect humans. Their predation on conifer seeds could conceivably impact forestry practices, but these impacts are negligible.

Conservation Status

Red crossbills have a large range and large population numbers, they are not currently considered threatened. There were large reductions in the numbers of red crossbills in areas logged during the 19th and 20th centuries, but some of those populations may have rebounded as forests re-grew. A combination of nomadism, adaptation to cold environments, high reproductive rate with abundant food supply, and early sexual maturity make red crossbills especially good at responding to variation in cone crop availability across a landscape. Their populations can rebound quickly when food resources are available. Red crossbills are frequently killed by cars when they take salt and sand off of roads.

Additional Links

Encyclopedia of Life

Contributors

Tanya Dewey (author), Animal Diversity Web.

References

Adkisson, C. 1996. Red crossbill (Loxia curvirostra). The Birds of North America Online , 256: 1-20. Accessed March 26, 2009 at http://bna.birds.cornell.edu/bna/species/256 .

Genard, M., F. Lescourret. 1987. The common crossbill Loxia curvirostra in the Pyrenees: Some observations on its habitats and on its relations with conifer seeds.. Bird Studies , 34: 52-63.

Hahn, T. 1998. Reproductive seasonality in an opportunistic breeder, the red crossbill, Loxia curvirostra. Ecology , 79: 2365-2375.

Knox, A. 1990. The sympatric breeding of Common and Scottish Crossbills Loxia curvirostra and L. scotica and the evolution of crossbills. Ibis , 132: 454-466.

Questiau, S., L. Gielly, M. Clouet, P. Taberlet. 1999. Phylogeographical evidence of gene flow among Common Crossbill (Loxia curvirostra, Aves, Fringillidae) populations at the continental level. Heredity , 83: 196-205.