Bird of the Month: White-winged Crosbill
Written by Andy McCormick
Andy McCormick, Volunteer and Former Board President of Eastside Audubon
A wonderful irruption of White-winged Crossbills has descended upon Washington this winter. This special bird has some unique characteristics.
The White-winged Crossbill as its name describes has a bill that crosses in much the same manner as you would cross your fingers. The bill of the White-winged Crossbill is narrow when compared to that of the Red Crossbill, but it functions in much the same manner. The birds are able to pry open a seed casing on a conifer cone and pull the seed out with their tongue. White-winged Crossbills forage primarily on black spruce, white spruce, and in Washington Engelmann spruce. Pictures and videos of foraging White-winged Crossbills can be seen at the Macaulay Library.
The White-winged Crossbill shares the genus Loxia, from the Greek, loxos¸slanting or crosswise, with the Red Crossbill (L. curvirostra) and the Cassia Crossbill L.sinesciuris) in North America. There are other crossbills in Scotland, Eurasia, and on the island of Hispaniola. The species epithet is composed from the Greek leukos, the color white, and petron, feather, referring to the white bars on the bird’s wing (Holloway).
A SOCIAL BIRD OF THE BOREAL FOREST
White-winged Crossbills are highly social and travel widely across their territory in the western boreal forest. Flocks move throughout the year. The primary motive for their wandering is their search for good conifer seed crops. Like Red Crossbills the White-winged will move when seeds are scarce, especially in warmer weather when cones drop their seeds.
Group foraging has been observed and data indicate that these birds are active feeders and communicators. Calls among the flock members vary with cone abundance creating a feedback mechanism for efficient cone crop assessment. When feeding is good the birds are relatively quiet. However, poor cone conditions will lead to increased vocalizations. As more birds respond to poor feeding, the flock calls can reach a crescendo and a unified departure (Benkman).
IRRUPTIVE AND NOMADIC
White-winged Crossbills are highly nomadic and travel in large flocks seeking good cone crops. Some researchers think, but have not proven, that some crossbill flocks traverse the continent during the course of a year. In keeping with its nomadic nature, the White-winged Crossbill can breed irregularly during the year depending on crop success. With good feeding the flock will settle for a few weeks. Most breeding in North America occurs from July to November and in good cone seasons these crossbills can have a second brood (Benkman).
The nomadic nature of crossbills creates difficultly for accurate research studies. Nesting locations vary from year to year. Researchers have learned that the female leads construction of an open cup nest on a horizontal limb of a spruce or other conifer. Usually, two to four whitish to blue eggs spotted with brown or lavender are deposited. Incubation probably lasts about two weeks. It is not known how many days nestlings need before fledging (Kaufman).
White-winged Crosbill
Scientific Name: Loxia leucoptera
Length: 6.5”
Wingspan: 10.5”
Weight: 0.91 oz (26 g)
AOU Alpha Code: WWCR
STATUS AND DISTRIBUTION
The White-winged Crossbill is a holarctic finch that spends the year in conifer forests from Alaska to Newfoundland and south to the Rockies and Cascades. Another subspecies (L. l. bifasciata) has a similar range from Scandinavia across Central Asia to the forests of China. The population of White-winged Crossbills is of least concern, but it may fluctuate, increasing during abundant crop years and gradually diminishing over poorer crop years (Kaufman).
Current logging practices are detrimental to White-winged Crossbills. The shorter rotation period for cutting trees reduces the abundance of conifer cones available to crossbills. A healthy conifer takes about 30 years to begin to produce cones and 60 years to reach maximum cone production. Recommendations to forest managers include extending the time between loggings of trees to give large conifers, especially spruce trees for White-winged Crossbills, time to develop good cone crops (Benkman).
Photo credit Scott Heron. References available upon request from amccormick@eastsideaudubon.org.