Red crossbill (Percna) COSEWIC assessment and status report: chapter 5

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Species Information

• Name and Classification
• Description

Name and Classification

Vernacular Names:

Vernacular synonyms (both current and historical) for the Red Crossbill in Newfoundland include Spruce Mope (Peters and Burleigh 1951), Large Spruce Bird (Reeks 1869), and Spruce Bird (Montevecchi and Wells 1987).

Subspecies Nomenclature:

Red Crossbills (Loxia curvirostra) in North America have historically been classified into a number of subspecies, based on morphological differences in body and bill size/shape, as well as differences in plumage characteristics (Griscom 1937). Further research has demonstrated that the variation in bill size of subspecies results in different conifer seed preferences (Lack 1944; Benkman 1993a) and that Red Crossbill taxa are separated by vocal distinctions that correlate with positive assortative mating (Groth 1993a).

Ornithologists have long recognized Red Crossbills found in Newfoundland as a distinctive crossbill variant, owing to a large body and bill size and darkish plumage. Bent (1912) first identified the Newfoundland subspecies of Red Crossbill in the scientific literature, and designated it Loxia curvirostra percna. This taxonomy is accepted in Noble’s (1919) subsequent publication on Newfoundland’s avifauna, and in the American Ornithologists’ Union (AOU) Checklist of North American Birds, 4^th edition (American Ornithologists' Union 1931). However, around this period, earlier collections of New World Red Crossbills were being re-examined, given the emergence of new crossbill subspecies. In 1922, Stresemann examined specimens at the Berlin Museum which had been identified as Loxia pusilla and/or Crucirostra americana by Gloger (1843, as discussed in Groth 1993b). Stresemann gave the larger specimens the designation pusilla (Groth 1993b). In 1934, van Rossem concluded that the Berlin pusilla specimens were morphologically matched to Red Crossbills from Newfoundland, although van Rossem did not consult any additional North American specimens. Thus, van Rossem replaced percna with pusilla for the Red Crossbill Newfoundland subspecies, even though Stresemann had concluded that the Berlin pusilla type came from Georgia (as discussed in Groth 1993b).

Griscom’s (1937) major work on crossbill taxonomy supported van Rossem’s ideas, and refers to the Red Crossbill Newfoundland subspecies as Loxia curvirostra pusilla Gloger. Griscom assumed that the Newfoundland subspecies wandered great distances, thus justifying that “the type [specimen] apparently came from Georgia” (Griscom 1937). The use of pusilla for the Newfoundland subspecies was adopted in Peters and Burleigh’s (1951) The Birds of Newfoundland and in the AOU’s Checklist of North American Birds, 5^th edition (American Ornithologists' Union 1957). This taxonomy is also used in Godfrey’s (1966) The Birds of Canada and also in the revised edition (Godfrey 1986). 

By the 1980s, authors such as Phillips (as discussed in Groth 1993b and Dickerman 1987) were reverting back to the use of percna in reference to the Newfoundland subspecies, recognizing that the use of pusilla was likely in error. Payne (1987), in a detailed study of variation within pusilla, concluded that percna is a distinct form, and not a synonym of pusilla. Phillips even suggested the elimination of subspecies names in favour of grouping North American crossbill types based on size similarities. Phillips’ research led him to suggest that percna be grouped with California Red Crossbills into a large-sized type Class III (as discussed in Dickerman 1987). 

In the early 1990s, Groth (1993b) published a major revision in North American crossbill taxonomy. This work was based on a study of the morphological, vocal, and genetic traits of the New World Red Crossbill ‘complex’ of types. Groth concluded that the Red Crossbill complex represents a group of eight reproductively isolated sibling species, and not subspecies. Distinct crossbill types that were identified in his analysis do not generally correspond to the traditional subspecies nomenclature. Many of the crossbill types overlap morphologically and geographically, making call type discrimination an essential feature of identification. Genetic analysis done for this study revealed that Red Crossbill types are very similar, showing genetic differences that are not as large as would be seen among different species within a single genus. Similarly crossbill species in the United Kingdom have also been found to be not genetically distinquishable (Summers and Piertney 2003). Groth (1993b) labelled Red Crossbills from Newfoundland as the Type 8 Red Crossbill, based on morphological differences, and based on one recorded call, which was different from all other recorded North American Red Crossbill calls. Groth (1993b) cautioned, “it is not known if mainland crossbills ever reach Newfoundland, nor is it known if Type 8 birds occur on the mainland.” Groth (1993b) stated that scientific binomial names are needed for the ‘species’ in the North American Red Crossbill complex, and he suggested that the name of the Newfoundland type is “most appropriately percna Bent 1912.” The name pusilla is likely inappropriate for this subspecies of Red Crossbill, as it corresponds most closely to crossbills of Type 2 (Groth 1993b). The American Ornithologists’ Union (1983) stopped publishing subspecies nomenclature after its 1957 5^th edition checklist but continued to endorse the use of trinomial subspecies nomenclature. Historical taxonomic revisions affecting the nomenclature of the Red Crossbill, percna subspecies are presented in Table 1.

Current Consensus?

Some recent scientific publications concerning this Red Crossbill subspecies use the subspecies name percna (see examples in Pimm 1990; Parchman and Benkman 2002). Other recent work advocates an adoption of Groth’s (1993b) type classification system for North American crossbills (Pyle 1997; Kaufman 1999; Sibley 2000), with this taxon classified as Type 8. 

Knox (1992) suggests that Red Crossbills are most correctly identified as “pseudospecies” because they are temporarily sympatric (when birds from widely different core populations occur together on irruptions), but are reproductively isolated populations. Knox (1992) argues that there is no need to consider many Red Crossbill subspecies as separate species because there is no evidence that they act as separate species when they are within their main ranges although he acknowledges that detailed information is lacking. Groth (1993b), however, concludes that North American Red Crossbills are sibling species: gene flow as a result of their vagility has not homogenized their morphology because the forms are reproductively isolated. 

Based on this conclusion, some authors have considered the promotion of Red Crossbill forms to full species status. DeBenedictis (1995), for example, indicates that the eight North American Red Crossbill types fit the contemporary species definitions, and show the same divergence as the Old World Red Crossbills that are recognized as separate species. He recognizes that additional research is required to make definitive assertions about the species statuses of the New World types. The possibility of full species status of the forms L. curvirostra has also been recently demonstrated in Europe (Robb 2000; Summers et al. 2002). These crossbills have sympatric distributions but probably reproduce assortatively based on call type discrimination.

Summary

The Red Crossbill taxon percna is a distinctive group. It is morphologically different from other North American Red Crossbill forms and is considered one of eight reproductively isolated forms found in North America. The past use of the subspecies name pusilla may have been in error, with the more accurate subspecies name for this Red Crossbill taxon being percna.

Description

Crossbills are medium sized finches identifiable by their unique crossed mandibles. North American Red Crossbills have no white wing bars, which distinguish them from the other North American crossbill species, the White-winged Crossbill (L. leucoptera). Adult male Red Crossbills are generally a dull red colour above and below, with the rump generally brightest, and the back dullest with some brown colouration (Godfrey 1986). Adult females have a generally greyish olive rather than red colouration, with yellowish rumps (Godfrey 1986). Flight feathers are a blackish brown in both males and females, as is the deeply notched tail (Godfrey 1986; Adkisson 1996). Juvenile Red Crossbills have streaked heads and bodies, and a pale grey colouration with hints of olive or yellow (Godfrey 1986), and are generally distinguished from adults by buffy edges on their wing coverts (Adkisson 1996). Immature male birds are variable, and may possess plumages intermediate between female and adult males (Godfrey 1986). Red Crossbills may not undergo regular seasonal moults, thus plumages can vary throughout the year (for example, males can range from deep brick red to reddish yellow or greenish; Adkisson 1996). Bill sizes and body sizes vary according to the subspecies of Red Crossbill (Adkisson 1996). In an examination of Canadian Red Crossbills, left and right bill crossover were found to occur with the same regularity (James et al. 1987).

The percna subspecies is larger, has a stouter bill and darker and duskier plumage than other North American Red Crossbills (Pyle 1997). Peters and Burleigh (1951) describe the adult male as “dull red, brighter on the rump, with wings and tail blackish,” the adult female as “dull olive-gray, with yellow on rump and often on under parts, wings and tail dark grayish,” and juveniles as “variable, ranging from olive-green to yellow to reddish.” Griscom (1937) points out that both sexes of the percna subspecies are readily recognizable by their dark, dull colouration and that with little practice, specimens of this subspecies can be easily identified. See figures Figure1 and Figure2 for photos of Red Crossbills from Newfoundland. Morphometric and bill measurements for Red Crossbills, percna subspecies, from literature and museum sources are presented in Appendix 1 and Appendix 2.

Figure 1:  Male Red Crossbill on Ornamental Austrian Pine, St. John’s, April 28, 2002

Photos © Dave Fifield and used with permission.

Figure 2: Male Red Crossbill Specimen from a Road Kill in Terra Nova National Park, 1997