Red Crossbill Life History

Habitat

Red Crossbills favor mature coniferous forests, especially spruce, pine, Douglas-fir, hemlock, or larch with recent cone crops. Although Red Crossbills mostly breed south of the forests of spruce, fir, and larch where White-winged Crossbills breed most abundantly, the two species forage together in white spruce and Engelmann spruce forests in late summer, when cone crops are extensive. In North America, Red Crossbill comprises at least 11 different “types” (distinguished in the field by their flight calls), many of which specialize on particular species of conifer. For example, the small-billed type 3 favors western hemlock, which has very small cones, whereas the largest-billed type 6, found in the Southwest, feeds on larger-coned pine species. Birders have begun to make audio and video recordings of Red Crossbill, both to identify the type involved and to identify the species of conifer in which they feed.

Food

Red Crossbills eat seeds of spruce, pine, Douglas-fir, hemlock, or larch. To obtain these seeds, they first grasp the cone with one foot (normally, the foot that is on the side opposite to which the lower mandible crosses). They insert the partly open bill between two of the cone’s scales, then close the bill, which widens the space between the scales, exposing the seed. They use the tongue and bill together to remove the seed. When feeding on closed cones of spruce, hemlock, and Douglas-fir, crossbills usually remove the cone from the branch, but if these cones are open, they leave them attached to the branch, as they do with almost all pine cones. Occasionally, they forage on fallen cones on the ground. Before swallowing the seed, they remove the seed coat. Important tree species for Red Crossbill include eastern white pine, pitch pine, Table Mountain pine, loblolly pine, lodgepole pine, red pine, ponderosa pine, Sitka spruce, Engelmann spruce, red spruce, black spruce, white spruce, western hemlock, eastern hemlock, Douglas-fir, and western larch. They sometimes eat seeds of birch and alder species, as well as box elder, along with many kinds of insects in early summer.

Nesting

Nest Placement

Nests, built mostly by the female, are usually sited in open rather than dense woodlands; nests are built inside dense foliage, on branches, next to or near the trunk, up to about 70 feet above the ground.

Nest Description

Bulky cup nests are built largely of conifer twigs, with the cup lined with grasses, weeds, seed-pod fibers, lichens, conifer needles, feathers, bark, or hair. Nests average about 9 inches across, and 2 inches tall, with the inner cup 2.4 inches across and 1 inch deep.

Nesting Facts

Behavior

Red Crossbills are social throughout the year, even during the nesting season, when pairs often nest close to each other in areas where cone crops are heavy. Nesting can commence at any time, but in North America, most Red Crossbills breed in late summer through early autumn and/or in late winter through early spring. In spring, when most songbirds begin to nest, many conifer seeds have not yet developed or become available, and so the later timing of Red Crossbill nesting seasons coincides with periods of greatest food availability. Males do not defend large territories, but they do have favored perches for singing and for making flapping-gliding flight displays, and they do chase other males that approach too closely. Between adult males, conflicts over cones, including threat displays, chases, and attacks, are not uncommon. Males often chase females when in search of a partner, and billing (touching bills together rapidly) and courtship feeding by the male help establish the pair bond. Males stay close to their partners during the nesting season, and partners select the nest site together. Red Crossbills appear to be monogamous in their mating system, and pairs sometimes raise two broods in a single nesting season when food is abundant. Both parents incubate the eggs and feed the young. When feeding, flocks of Red Crossbills move through woodlands with what seems a “nervous” energy, flying and calling as they go from tree to tree. Some scientists have speculated that their contact calls convey information about the quality of feeding conditions in each tree—perhaps the accessibility of seeds, seed size, or other information. Calling in such contexts would improve the flock’s feeding efficiency, allowing them to pass over the inferior cones quickly for the better ones. During irruption periods, when flocks migrate long distances, observers often report this apparently restless behavior, as the crossbills try to locate food in unfamiliar environments.

Conservation

Red Crossbill populations decreased slightly or held steady between 1970 and 2019, according to the North American Breeding Bird Survey. Partners in Flight estimates a global breeding population of 26 million and rates them 8 out of 20 on the Continental Concern Score, indicating a species of low conservation concern. Crossbills gather grit on roadsides, making them vulnerable to vehicle strikes, and to possible ill effects from ingesting salt and other chemicals used to treat roads in winter. Logging of older-growth forest reduces food available to Red Crossbills, as many conifer species reach maximum productivity in their seventh decade or later. Extensive forest fires and outbreaks of pine beetles may temporarily reduce habitat and food available to Red Crossbills. In the early years after forest fires, crossbills can be common in burns because many of the dead trees (especially lodgepole pine) still have cones on them.

Credits

Adkisson, C. S. (1996). Red Crossbill (Loxia curvirostra), version 2.0. In The Birds of North America (A. Poole, Editor), Cornell Lab of Ornithology, Ithaca, New York, USA.

Lutmerding, J. A. and A. S. Love. (2020). Longevity records of North American birds. Version 2020. Patuxent Wildlife Research Center, Bird Banding Laboratory 2020.

Partners in Flight. (2020). Avian Conservation Assessment Database, version 2020.

Sauer, J. R., D. K. Niven, J. E. Hines, D. J. Ziolkowski Jr., K. L. Pardieck, J. E. Fallon, and W. A. Link (2019). The North American Breeding Bird Survey, Results and Analysis 1966–2019. Version 2.07.2019. USGS Patuxent Wildlife Research Center, Laurel, MD, USA.

Sibley, D. A. (2014). The Sibley Guide to Birds, second edition. Alfred A. Knopf, New York, NY, USA.

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