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Red Crossbill

Loxia curvirostra

Order:
Passeriformes
Family:
Fringillidae
Sections

Demography and Populations

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Figure 20. Relative abundance of Red Crossbill mostly during June in the United States.

Based on data from the North American Breeding Bird Survey, 2011–2015. See Sauer et al. (2017) for details.

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Figure 21. Regional trends in Red Crossbills mostly during June in the United States.

Based on data from the North American Breeding Bird Survey, 1966–2015 (Sauer et al. 2017). Data show estimates of annual population change over the range of the survey; areas of increase are shown in blue and declines are shown in red. See Sauer et al. (2017) for details.

Measures of Breeding Activity

As in White-winged Crossbill (135), the Red Crossbill has responded to extreme variability in conifer seed crops by evolving nomadic wandering behavior, early onset of sexual maturity, opportunistic breeding, and rapid succession of broods. Other adaptations include tolerance of repeated cooling, and the slow development of young when food is relatively scarce (47, 149).

Age at First Breeding; Intervals Between Breeding

Many observers have encountered birds in immature plumage showing evidence of breeding activity (e.g., 186, 26, 187); in summer, males and females with incomplete skull ossification and in immature plumage had enlarged gonads (T. Hahn, personal communication).

Repeated nesting in quick succession is possible; a captive pair in Michigan raised 4 broods of 4 young each in a single year, starting egg-laying while still feeding the previous brood (142). Such multiple broods may result when local seed crop is exceptionally large (47), as found in White-winged Crossbill (135). Male takes over sole responsibility for young of the first brood when female incubates the new clutch (171, 32). One pair started building a new nest 3 d after nestlings from first nest were depredated (194).

Clutch

Usually 3 eggs (171, 132), uncommonly 2 or 4 eggs, and exceptionally 5 or 6 eggs (47, 149, 32, 194). Seasonal variation in clutch size was not detected by Clouet (194), but mean clutch size tends to increase both with latitude from 3.3 eggs in Algeria, 3.4 eggs in French Pyrenees, and 3.7 to 3.8 eggs in England and the Netherlands (data summarized in Clouet [194]), and with increases in cone crop size (201). No information on number of clutches produced by female in the wild.

Annual and Lifetime Reproductive Success

Few data. Proportion of eggs producing fledglings ranges from 33% (171) to 48% (149). Of breeding attempts monitored in the Pyrenees, 28% fledged young, but fledging success varied from 6 to 79% in the Netherlands (194).

No information on lifetime reproductive success in wild birds.

Number of Broods Normally Reared per Season

No information on annual number of broods produced by wild birds, but it is expected that 1–3 broods and perhaps up to 4 broods are produced per year, as in White-winged Crossbill (135).

Proportion of Total Females that Rear at Least One Brood to Nest-Leaving or Independence

No information.

Life Span and Survivorship

The longevity record for Red Crossbill in North America involved a female banded as an adult in South Dakota and found dead 6 yr, 1 mo later in South Dakota (204); the longest interval between first and last capture in the Pyrenees was 4 yr (205). Captive Red Crossbills live up to 8 yr (142). The maximum age of Cassia Crossbill in the wild is 9 yr (CWB).

Apparent adult annual survival was estimated at 0.46 in the Pyrenees (129). At another site in the Pyrenees, annual survival was greater for males than females (0.51 and 0.30, respectively), but also decreased with wing length, which was interpreted to result from longer-winged individuals being more dispersive with some representing northern vagrants and thus more likely to emigrate and less likely to be recaptured (205). For Cassia Crossbill, apparent annual adult survival varied among years from 0.75 to 0.34, with the smaller value occurring during a large population decline (20). Male Cassia Crossbills have higher apparent annual adult survival than females (206).

Disease and Body Parasites

Diseases

Haemoproteus infections are most evident in adults of call types 2, 3, 4, and 5 between May and October with parasite densities higher in males than females, and increasing with increases in testosterone levels (207).

Body Parasites

Ectoparasites include scaly-leg mite, Knemidokoptes jamaicensis (Acari: Knemidokoptidae) (208), feather lice, Brueelia limbata and Philopterus curvirostrae (Mallophaga: Philopteridae) (D. Clayton, personal communication), and Diptera: Hippoboscidae (CWB); hippoboscid flies seem most prevalent on recently fledged birds (T. Hahn, personal communication). Scaly-leg mite was found to adversely affect adult survival in the Cassia Crossbill, especially larger-billed males (206). A pattern of a higher incidence of scaly-leg mites in larger individuals was also found in a worldwide examination of Red Crossbill specimens (208). In Europe, Red Crossbills tend to have elevated loads of feather lice compared to 2 other finch species, perhaps because their mandibles do not occlude near the tip preventing effective preening (209).

Causes of Mortality

Immatures probably suffer high mortality during the first several months of independence because of inefficient foraging (see Santisteban et al. [20] for Cassia Crossbill) and from being subordinate to adults (see Benkman [183] for White-winged Crossbill). Eurasian Sparrowhawk was found to prey on Red Crossbill during a year when crossbills were especially common (193). Many crossbills are killed by traffic on salted and sanded roads (170, 132); see also Diet and Foraging: Nutrition and Energetics.

Exposure

Little information. In the Pyrenees, 46% of nest failures attributed to bad weather, with breeding success decreasing as average snow depth increased (194).

Predation

See Behavior: Predation. In the Pyrenees, 31% of nest failures were attributed to predation (194).

Competition with Other Species

The main seed competitors are seed and cone insects, which destroy cones and consume seeds especially during seed development (195), other crossbill call types, and tree squirrels (particularly Tamiasciurus in North America, but also Sciurus in both the Old World and New World), which remove closed cones from trees (157, 210, 158). Seed competition is likely most intense over conifers producing the most consistent annual seed crops (157), which explains in part why crossbills are up to 20 times more abundant in Rocky Mountain lodgepole pine forests lacking red squirrel than in nearby forests where red squirrel is present (211).

Range

Initial Dispersal from Natal Site

No information for North America. In Europe, there are records of Red Crossbills moving up to 3,000 km between natal and breeding sites (127).

Fidelity to Breeding Site and Winter Home Range

Fidelity to breeding sites is likely uncommon because the intervals between large cone crops at a given location for many conifers (e.g., 3–5 yr) may exceed the lifespan of most crossbills. Nevertheless, individuals may return to rich patches with some regularity, especially following a year(s) of poor cone crop as exemplified by a Type 4 bird captured during 2 summers (1988 and 1990) on Shaw Island, Washington with an intervening year with few cones or crossbills (T. Hahn, personal communication). Fidelity (residency) occurs in the few cases where seed crops are unusually stable (129); e.g., individuals of types 2 and 5 have been recaptured yearly at a banding site for up to 4 yr in an area where resources are exceptionally stable (128). In North America, 56 Red Crossbills have been recaptured at locations away from their original banding location (U.S. Geological Survey Bird Banding Laboratory data); the median distance moved was 29 km and there were 8 movements > 500 km, with a maximum of 1,955 km (128). In Europe, there are records of Red Crossbills moving up to 3,000 km between breeding sites (127).

Dispersal from Breeding Site

Limited evidence of fidelity to breeding site among years for most call types, but individuals might return to rich patches with some regularity at various intervals throughout their lifespan (T. Hahn, personal communication).

Home Range

Little information. Breeding pairs may forage over 500 m from nest (171, 149). Apparently not territorial, as in White-winged Crossbill (184).

Population Status

Numbers

Using data from the North American Breeding Bird Survey (BBS), the Red Crossbill population was estimated at 7,800,000 individuals for the United States and Canada from 2005–2014 (212). Extreme variability of food supply and nomadism mean that Red Crossbill numbers are highly variable within a habitat (135, 32), and the species is often absent or occurs in very low numbers over large areas. High reproductive potential leads to quick recovery from losses due to emigration and subsequent starvation (47).

Trends

Owing to the highly variable abundance seen in Red Crossbill populations, and surveys often occurring in months that don't capture crossbill breeding events, analyses of BBS data are difficult and results indicated few population trends within the U.S. and Canada from 1966–2015. For the Survey-wide region, BBS data suggested a 0.8% annual decline from 1966–2015, however, the 95% credible interval included zero (213). A notable exception was the Northern Rockies region, where the species was estimated to have declined by 2.1% annually from 1968–2015 (213). Over a 45-yr period (1970–2014), BBS data indicated that the breeding population in the U.S. and Canada decreased by an estimated 12% (212).

A putative decline of the Red Crossbill in the northeastern U.S. after logging of old-growth forests (214) seems likely, and is supported by population increases in New Brunswick and Nova Scotia in the 1960s and 1970s following forest recovery (215); however, no trends were evident in these provinces based on 1966–2015 BBS data (213). Red Crossbill (L. c. percna) has become rare on Newfoundland based on Christmas Count data in Terra Nova National Park, most likely because of competition from the red squirrel, a species that was introduced there in 1963 (65, 83, 84).

Population Regulation

The abilities of crossbills to track the spatiotemporal fluctuations in seed crops is evident from the positive correlations between crossbill abundance and seed crop size (216, 201, 210). In spite of such tracking, variable percentages of the seed crop are consumed, ranging from 4–17% of scots pine in Scotland (210), 15–41% of mountain pine in the Pyrenees (164), to over 80% of scots pine in southern Spain (217), indicating that the extent of food limitation varies among years and locations. Food limitation is likely greatest during the period between most seeds being shed and the next seed crop developing in summer (119), and during years of small seed crops (210) and especially extensive cone failures that cause massive movements (218, 123, 126, 47, 127) often into nonconiferous regions where starvation probably occurs on large scale (47). The combination of large population size and small cone crops causes irruptions in North America (16), however, irruptions away from forests with moderate cone crops have occurred in Europe, suggesting that population size interacts with seed availability in regulating populations (47, 127). Although in England, the Eurasian Sparrowhawk has been found to prey extensively on Red Crossbill when the latter species was breeding and abundant (193), predators are unlikely to have widespread impact on population size (14).

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