Crossbills

by Dave Hicks

The first time I ever remember noticing an unusual bird was on the way home from the school bus on a winter morning long ago in New York. My parents always kept a bird feeder in the winter, so I was accustomed to Fox Sparrows, Evening Grosbeaks and other winter visitors. But I knew that a bird with a red body, black wings, and an extremely odd-looking bill was some- thing I’d never seen before. My father quickly found an illustration in the book he considered to be the ultimate author- ity on birdlife, Pearson’s Birds of Amer- ica, illustrated by Louis Agassiz Fuertes. The bird was, of course, a Crossbill. Crossbills are classified in the genus Loxia, in the finch family (Fringillidae). In most bird guides, you will find this group at or near the end of the book.

Most bird guides list two species, the Red Crossbill (Loxia curvirostra) and the White-winged Crossbill (Loxia leucoptera), in North America. Both species are impossible to mistake if the X-shaped pattern made by the tweezer- like extensions of the upper and lower jaws are seen. Adults are approximately sparrow-sized. In both species, males have red bodies and dark wings, while the females are greenish with dark wings. The wing bars that give the White-winged species its name are prominent.

Seeing a crossbill of either species is an unusual event in much of the east- ern US. Crossbills are habitat and diet specialists, closely tied to coniferous forests and the seeds of their dominant pines, spruces and firs. These seeds are richer in protein and fat than are most seeds, and crossbills even feed their young mostly on regurgitated seeds. Adults do mix up their menu to some extent by adding seeds of other species, tree buds, and some insects. Because they are so closely tied to conifer for- ests, crossbills leave their range in Alaska, Canada, the mountains of the western US, and the northernmost states only in times of food shortage, a pattern called an irruption. Audubon Christmas Count records indicate that 1964 was probably the year I saw the crossbills, as this was a year when large numbers were seen in New York State. Some other members of the finch family fol- low similar irruptive patterns, such as Pine Grosbeaks, Purple Finches, Pine Siskins, Common Redpolls, and Eve- ning Grosbeaks.

Crossbills are distinguished by the overlapping, tweezer-like extensions of their bills. They give crossbills access to seeds nestled among the scales of cones. The birds can extract thousands of seeds per day with their highly effi- cient “tableware”. They use the exten- sions to pry the cone scales apart, then extract the seeds with their tongue. (You can see an excellent video of feed- ing White-winged Crossbills on You-tube at: http://www.youtube.com/watch? v=1NvU8WG9bg0. Despite their spe- cialized beaks, crossbills can feed from the ground and may even visit feeders.

The bill extensions can cross in two different ways, with the extension of the lower jaw to the left or to the right of the upper jaw. Depending on their personal configuration, individual birds approach cones from the left or the right, and spiral around the cone clockwise or counterclockwise while feeding. It is unknown whether the left vs. right pattern is due to genetic fac- tors, the environment, or some combi- nation. However, the ratio of lefties to righties is very close to 1:1. Hatchlings do not have the extensions, but gradu- ally develop them over their first few weeks of independent life. As the exten- sions grow, the birds become more effi- cient at feeding from cones.

The Red Crossbill feeds mostly on spruce cones, the White-winged Cross- bill primarily on larch and hemlock. However, some Red Crossbills in the western US feed on pines and hem- locks. As well as unusual diets, these populations have distinctive calls. Further Red Crossbill variants also exist. So far, 9 different call varia- tions have been recognized, and birds with different calls tend not to mate with each other. There have been some suggestions that each call type should be classified as a separate species. If that classification is accepted, we would have ten species instead of just two. You can find out more about this situa- tion and listen to sound files of calls at http://ebird.org/content/ebird/news/intr oduction-to%20crossbill-vocalizations. David Sibley, of field-guide fame, has a nice discussion at http://www.sibleyguides.com/2010/09/r ed-crossbill-call-types-act-like- species/. A long and detailed descrip- tion of many of the variants can be found at:

http://www.uwyo.edu/benkman/pdfs %20of%20papers/benkman_2007_colo rado_birds.pdf.

Red and White-winged Crossbills have overlapping, though distinct, dis- tribution patterns. Both species have ranges that cross the North American continent from Alaska to Newfound- land. The White-winged Crossbill in general occurs further north, reaching the shores of James Bay. The Red Crossbill has a somewhat more south- erly distribution in Alaska and Canada, but also occurs in the western moun- tains (extending well into Mexico), and in the southern Appalachians. Both spe- cies disperse widely during irruption years, with the Red Crossbill reaching more southerly areas in Texas and Georgia. In Indiana, both species are sporadic. The Red Crossbill has been reported for the state in only 14 of the last 40 Christmas Counts, and the White-Winged only 5 times. Neither species has been seen in a TAS Christ- mas count, probably due to lack of ex- tensive conifer forests in our count area.

Both of the North American spe- cies also occur across much of Europe and Asia. There are at least two further species of Crossbill in Europe (the Par- rot Crossbill, Loxia pytyopsittacus and the Scottish Crossbill, Loxia scotica). Finally, the Hispaniolan Crossbill (Loxia megaplaga) occurs in the moun- tains of Haiti and the Dominican Re- public.

As might be expected of birds that are so closely tied to one main food resource, the breeding behavior of Crossbills relates more to food avail- ability than season. Unlike most tem- perate-zone bird species, crossbills re- produce during most of the year. It is not unusual for them to nest in the late winter or very early spring, at a time when conifer seed availability is high- est.

Although they are unusual birds in our region, both North American Cross- bills are considered to be at low risk of extinction. However, Red Crossbills have been declining in Newfoundland; the suspected reason is competition with introduced red squirrels.

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