This week’s Bird of the Week, compliments of the Weminuche Audubon Society and Audubon Rockies, is the red crossbill.
Within its range in North America, fluctuations in presence, abundance and even nesting time of the red crossbill is linked with food availability. It is one of the nomadic finches of coniferous woodlands. Along with evening grosbeaks, pine siskins, pinyon jays and nutcrackers, the red crossbill is tied to the unpredictable nature of cone production by conifers.
Red crossbills live in mature forests, especially those with spruce, pine, fir, hemlock or larch. Both logging of older trees which produce seeds more reliably and destructive forest fires reduce the food supply and abundance of these birds.
Only the males of this medium-sized finch are red, with females colored yellowish and immatures streaked brown. All display darker wings and the criss-crossed bills for which they are named. Ten different call types or ecomorphs are recognized whose calls and tree preference differ enough to usually prevent interbreeding.
In these birds, bill structure is an amazing example of adaptation to a food source, with different bill sizes corresponding to different cones. The red crossbill places the curved tips of its slightly open bill under the scale of a cone and bites down. This forces the scale up and exposes the seed, which is then extracted by the bird’s long tongue and hulled before it is swallowed. One bird can consume 3,000 seeds per day.
Red crossbills are not born with crossed bills. As the immature bird develops and starts feeding on its own, it twists its beak in one direction or another over and over until the growing tips become crossed. There is an equal chance of the tips crossing left to right or right to left, which in turn determines which seeds the bird can extract from a closed cone.
These birds exist in social flocks year-round, calling to each other with their secret language. Calls may communicate among the flock the quality of feeding conditions in a tree and keep it together when moving from place to place. When feeding at a good seed source, the flock may be quiet, with the only evidence of its presence the sight of seed wings floating to the ground from high up in a tree.
For information on events, visit www.weminucheaudubon.org and www.facebook.com/weminucheaudubon/.
