“They call me the wanderer, yeah the wanderer, I roam around around around…” – Dion DiMucci, “The Wanderer”
Birds are, in many ways, defined by their relationships with their food. Perhaps no group of species exemplifies this effect better than the crossbills. Uniquely adapted to prying open closed conifer cones and extracting the seeds inside, crossbill populations are nomadic, irruptive, and show a significant amount of variation even within a single species. The Red Crossbill is the most common breeding species of crossbill in Massachusetts, but one may have a better chance of predicting New England weather than predicting where and when a Red Crossbill will show up.
The eight North American “types” of Red Crossbills, which are subject to frequent division and re-interpretation, each possess a unique call as well as subtle but important differences in size and bill morphology. Despite frequently occurring in the same area at the same time, their distinct calls seem to keep these “types” reproductively isolated from one another. Those small differences in size, strength, and bill shape allow each type to most effectively deal with one particular sort of cone. Black Spruce, Red Spruce, Eastern Hemlock, and our various pine species all attract their own crowds of Red Crossbills, which use their unique bills to pry open closed cone scales and crack the seeds inside. Since the highly nomadic crossbills appear in Massachusetts only when a poor seed crop in other regions forces them to move, Red Crossbills remain a rare breeding species in Massachusetts. So far in Atlas 2, activity so far has been concentrated around the Quabbin.
Although conventional wisdom holds that Red Crossbills will breed in any season, research suggests that they are unlikely to do so in late autumn. All other times of the year seem to be fair game, though, particularly late fall and early spring. As suits such a peripatetic bird, males do not defend territories, singing only in order to attract a mate. Red Crossbill song is a series of short, trilly whistles given in matched sets of two, three, or four notes. Sometimes the song has an accented ending, and the delivery of each note is paced similarly to the skipping of a lawn sprinkler between cycles: chirp-chirp-chirp-twee-twee-twee- twee-chirple. The male and female make a joint decision when selecting a nesting location, but the female is primarily responsible for construction. The skeleton of the nest is built with conifer twigs, and varying amounts of lichen and moss insulation are added depending on the time of year. The lining typically consists of conifer needles, hair, and feathers. Female Red Crossbills lay relatively small clutches, often only two or three eggs, though clutches up to five are certainly not unheard of. All incubation is done by the female while the male brings her food on the nest. For the first few days after hatching, especially in cold weather, the female may spend most of her time on the nest, and the entire family will be reliant upon the male’s provisioning. The parents vomit up a nutritious seed paste for the young birds, which open their eyes and grow their entire set of feathers over the course of about two weeks, though their bills will not develop the distinctive cross until about one month of age. The young are soon accompanying their parents on foraging trips, which may include visits to bird feeders. These feeding stations offer the young birds accessible nutrition as they master the tricky art of opening conifer cones. Red Crossbill movements after breeding are just as difficult to predict as their movements before breeding; birds may come for the first time to Massachusetts with still-dependent young in tow while others depart the Bay State as soon as their chicks can fly proficiently.
All historic information in the text comes from Mass Audubon's Breeding Bird Atlas 1 or the Cornell Lab of Ornithology's "Birds of North America" site (bna.birds.cornell.edu/bna) unless otherwise stated.
Photo credit: Elaine R. Wilson, www.naturespicsonline.com. Licensed under the Creative Commons Attribution-ShareAlike 3.0 Unported License.