Red Crossbill, percna subspecies
1.1 Species Description
Crossbills are medium-sized finches with crossed mandibles, which allow them to forage on the seeds of conifer cones. Red Crossbills are associated with conifer forests on the island of Newfoundland and can be distinguished from congeners of insular Newfoundland by the crossed mandibles in combination with the lack of white wing bars, which are characteristic of White-winged Crossbills (Loxia leucoptera) (COSEWIC 2004). Adult males are mostly red with some brown shading, whereas adult females are greyish olive with yellowish rumps (Godfrey 1986). Both males and females have blackish brown flight feathers and deeply notched tails (Godfrey 1986; Adkisson 1996). Juveniles are similar in appearance to adult females and are usually pale grey with some olive and yellow. They can be distinguished from adults by their streaked heads and bodies as well as their buffy wing coverts (Godfrey 1986; Adkisson 1996). Red Crossbills often forage in flocks.
The percna subspecies is distinguished from other North American Red Crossbills by its larger body, stouter bill, and darker, duskier plumage. However, owing to the difficulty of identifying subspecies by morphology alone, vocalization may be the best method of distinguishing different Red Crossbill types in the field. The percna subspecies is considered one of eight reproductively isolated forms found in North America and is believed to have its own distinct call (Groth 1993).
Since the release of the COSEWIC status report (COSEWIC 2004), additional information on population and/or distribution of percna has become available. Recent studies of congeners in Europe stress the importance of vocalization for Red Crossbill identification (Bijlsma 2004; Edelaar and Terpstra 2004). Edelaar and Terpstra (2004) support Benkman’s (1989) and Groth’s (1993) suggestions that North American Red Crossbills likely represent distinct species and not subspecies; these suggestions were based on studies of morphological, vocal, and genetic traits.
1.2 Distribution of Red Crossbill
For a more detailed summary of the species’ range, refer to the COSEWIC status report (COSEWIC 2004).
1.2.1 Global Range
Red Crossbills occur throughout the boreal forests of North America and Eurasia and southward through the coniferous forests of northern Spain, northern Africa, the Mediterranean islands, northern India, southern China, Japan, and the northern Philippines (Godfrey 1986).
1.2.2 Canadian Range
Godfrey (1986) reports that in Canada, Red Crossbills breed in the coniferous forests of southern Yukon, southwestern Northwest Territories, all of British Columbia (including coastal islands), Alberta (in the south, confined to the western mountainous region), northwestern and central Saskatchewan, southern Manitoba, central and southern Ontario (except the extreme southwestern region), southern Québec, New Brunswick (except possibly the northwestern region; Erskine 1992), Prince Edward Island, Nova Scotia, and Newfoundland (but are absent from Labrador) (Todd 1963; Godfrey 1986).
The percna subspecies has been identified as extending throughout Newfoundland, with occasional irruptions in the Maritimes. The COSEWIC status report indicated that during years of low cone crops, the percna subspecies has been observed in Ontario, Québec, New Brunswick, and Nova Scotia (COSEWIC 2004), as well as potentially in the bordering northeastern U.S. states (Dickerman 1987). It is not known if percna has bred in Labrador, as breeding records for Red Crossbill are unsubstantiated (Todd 1963). Their insular Newfoundland range is not fully understood, as it is not clear if there are core breeding areas other than their association with coniferous forests (COSEWIC 2004). Canadian range is illustrated in Figure 1.
1.2.3 Percentage of the Global Distribution in Canada
The percna subspecies is believed to nest only in insular Newfoundland, Canada.
1.3 Population Sizes and Trends
Quantitative information does not exist to allow the assessment of historical population numbers or population trends for Red Crossbills in Newfoundland. However, they were once considered abundant, with numbers comparable to those of White-winged Crossbills (COSEWIC 2004). Since the mid-1900s, sightings of this species have greatly diminished, and the population is believed to have experienced a population decline upwards of 75% per decade during the period from 1968 through 2002 (based on Newfoundland Christmas Bird Counts; COSEWIC 2004). The status report suggests that the current total population size is 500–1500 individuals, but states that there is uncertainty associated with this estimate (COSEWIC 2004). This uncertainty is likely due to the sporadic and inconsistent nature of the survey effort across percna’s range, as well as a lack of surveys targeted specifically at crossbills.
Figure 1. Canadian range map for the Red Crossbill (Loxia curvirostra) (from Adkisson 1996).
1.4 Biological Needs, Ecological Role, and Limiting Factors
Due to their bill morphology, crossbills are highly specialized for foraging in conifer habitats. This habitat is also important for roosting and nesting (Adkisson 1996). Red Crossbills are locally irruptive, and their presence in an area is usually considered reflective of cone abundance. They often forage in flocks, suggesting the importance of social behaviour, and nest at any time of the year, based on cone availability. However, very little is known about the specific needs or life history of percna.
Survival and recovery of percna may be limited by changes to habitat and/or food abundance, possibly resulting from a combination of anthropogenic and non-anthropogenic factors (COSEWIC 2004). Interspecific competition, Allee effects,  and the cumulative effects of all of these factors could also influence Red Crossbill survival.
1.5 Habitat Needs
As previously described, Red Crossbills are believed to require a mosaic of cone-producing conifers for foraging, roosting, and nesting (COSEWIC 2004). However, owing to their irruptive behaviour and ability to breed at any time of the year, based on cone availability, Red Crossbill habitat associations are difficult to identify and are unknown for percna at this time. Knowledge gaps regarding habitat associations are considered a priority for future research.
Generally, large-billed crossbills are associated with large cones, such as pine; recent observations of Red Crossbills in Newfoundland have included a number of sightings in pine stands (COSEWIC 2004). Native red pine (Pinus resinosa) and eastern white pine (P. strobus) stands in particular are believed to have been historically important habitat for Red Crossbills in Newfoundland and may currently be linked to their survival (see section 2.2.2; W. Montevecchi, pers. comm. 2005). Benkman (1993a, 1993c) and Parchman and Benkman (2002), however, contend that percna is adapted to foraging on the seeds of black spruce (Picea mariana) in Newfoundland and argue that the cones of this species are different from the cones of mainland black spruce. Unfortunately, Parchman and Benkman (2002) do not indicate whether cones of mainland conifers are unexploitable by percna, except to suggest that differences arose due to mainland spruce evolving under predation by both crossbills and squirrels, whereas Newfoundland spruce have evolved under pressure from crossbills only (Benkman 1993c). Research to compare the cones of black spruce on the mainland with those of Newfoundland black spruce is necessary to assess the contention by Benkman and colleagues that the scales of Newfoundland black spruce cones are thinner than those of black spruce cones on the mainland; this study was based on a minute and geographically restricted sample (W. Montevecchi, pers. comm. 2005).Other conifer species exploited by Red Crossbills include white spruce (Picea glauca), balsam fir (Abies balsamea), and tamarack (Larix laricina), and there is evidence that Red Crossbills, including those in Newfoundland, also forage on various non-conifer food sources (Peters and Burleigh 1951; Payne 1972; Benkman 1993a; B. Mactavish, pers. comm. 2005). Furthermore, it is likely that all conifers present on the mainland would also be accessible to any percna occurring there.
The Allee effect is a biological phenomenon based on the positive relationship of population density with per capita population growth: i.e., the per capita birth rate decreases as population density decreases.
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