Friday, March 12, 2004
When and where seen: All around town. I have a pair regularly visiting my suet feeder. There were 29 birds recorded in the Carlisle Christmas Bird Count for 2003. You are more likely to see one this winter than in any winter since 1997.
Word for the day: Irruptive — used to describe populations that show an irregular increase in numbers. Red-breasted nuthatches are irruptive; they may move south in large numbers in the fall or they may remain in their northern territory if there is a good crop of cones.
Another word for the day: Supercilium — Latin for eyebrow, used in ornithology to describe what would otherwise be called an "eyebrow." It's not that ornithologists are supercilious highbrows; every branch of science has its specialized vocabulary.
Distinguishing characteristics: Of the four species of nuthatches in North America, only the red-breasted and white-breasted are seen in New England. The sharp white supercilium and black eye stripe distinguish the red-breasted nuthatch from the white-breasted, to say nothing of the breast — it's too soon after the Superbowl for more discourse on that subject. Of the two species, the red-breasted nuthatch is the smaller bird, about four and a half inches from tip of beak to tip of tail, more than an inch shorter than the white-breasted. The person who named the red-breasted nuthatch may have trained at the French impressionistic school of bird naming. They weren't thinking cardinal red or tanager; more squirrel red or fox. The male nuthatch looks like he didn't take the option for rust proofing his under-carriage, and the female has a pale faintly-orange belly. Nuthatches are easily recognized by the way they walk head-first down tree trunks, stopping and starting as if they have water in their gasoline. It is thought that the head-first downward behavior allows them to find food overlooked by other birds like the brown creeper and woodpeckers that must climb upwards because they need to brace themselves with their tail. Nuthatches climb by using only their strong legs and long toes. This unique capability is the source of another common name, the upside-down bird.
Nesting: Red-breasted nuthatches nest in cavities. Unlike the white-breasted nuthatch which looks for an existing cavity, the red-breasted is much more likely to excavate its own, but may occasionally use a ready-made cavity or a man-made birdhouse. Nuthatches create a "not-welcome" mat by smearing tree pitch around the entrance to their nest, sometimes over an area of a few inches, perhaps to discourage other birds or insects from entering. The Stokes' birdhouse book reports "beetle sweeping" behavior in which the nuthatch takes a beetle in its beak and rubs it around the nest entrance as if sweeping a porch. The hapless beetle, as part of its defensive reaction, exudes chemicals which, like the pitch, are thought to keep predators away from the nest.
References: David Allen Sibley, The Sibley Guide to Birds; Donald and Lillian Stokes, The Complete Birdhouse Book; www.birdnature.com for the nuthack information; http://birds.cornell.edu/birdhouse/bird_bios/speciesaccounts/rebnut.html.
© 2004 The Carlisle Mosquito