Introduction

Male White-winged Crossbill, CT, 19 January.

Figure 1. Distribution of the White-winged Crossbill

In North America, White-winged Crossbills (L. l. leucoptera) occupy boreal coniferous forests from Alaska to Newfoundland and south into the Washington Cascades, the central Rocky Mountains, and the northeastern states. The other race of this species breeds in the Palearctic from northern Scandinavia to Siberia (L. l. bifasciata). Like other crossbills, this species is specialized for foraging on seeds in conifer cones, and much of its behavior and ecology can be understood in terms of tracking this highly variable food resource. Often traveling in large flocks, these birds are highly efficient at finding and extracting conifer seeds, using their crossed bills to wedge open cone scales and then lifting seeds free with their tongues. Individuals can eat up to 3,000 conifer seeds per day, although their specialized bill makes them much less efficient than other finches at exploiting non-conifer seeds.

Shifts in the diet of this species reflect changes in the rates at which seed from different conifers can be consumed, and crossbill movements between areas are often timed to exploit developing cone crops. Breeding is opportunistic and can occur throughout most of the year, as long as food intake is sufficient for the female to form eggs and raise young. Although they can be locally abundant, nomadism has limited field studies of this and most other crossbills.

Loxia megaplaga, the Hispaniolan Crossbill, was considered a subspecies of L. leucoptera for many decades, but on the basis of vocal, morphological, and genetic divergence the taxon generally is treated as a species now. Given marked differences in voice, coupled with morphological (and posited ecological) differences, Old World and New World L. leucoptera also may be species rather than subspecies.

There is a growing need to understand how changes to the boreal forest and to North America’s climate are likely to impact populations of this crossbill. Most population surveys (e.g., Breeding Bird Survey) occur south of the main distribution of the species, so the implications of recent population trends are unknown. Although research on individual movements, demography and life history would be challenging with current technologies, such information would be valuable for both basic and applied reasons.