The Dive Note of the Anna Hummingbird
The Dive Note of the Anna Hummingbird.
To watch a male Anna Hummingbird (Calypte anna) make a “power dive” is a common but always thrilling experience to bird observers. Usually the dive is executed near or over a mate or an intruder. Hunt described the character of the dive in 1920 (Condor, vol. 22, pp. 109-110, fig. 27). The ascent before the dive usually is accompanied by vocal notes fittingly described as “zeezy-seezy-zeezy-zee” by Grinnell and Storer (Animal Life in the Yosemite, 1924, p. 353). In the steep drop of the dive no sound is made, but the instant the bird turns upward, a sharp note is produced. Various writers have described this note as kilp, plifi, and speck. The origin of this note has been the subject of considerable speculation. However, the consensus of opinion is that it is produced by flight or tail feathers.
Assuming this to be correct, I conducted a series of experiments with various feathers. Individual feathers and whole tails and wings were held in a swift current of air. The only promising response in these tests came from outermost tail feathers, which are narrower than the others (fig. 24). Then, in an effort to duplicate the conditions at the bottom of the dive, I attached an outer tail feather to a slender strip of bamboo. By whipping this through the air a note was produced, which was almost identical with that produced by the bird. No other feathers produced this note. This experiment was demonstrated before the Cooper Club at its annual meeting in Fresno, on April 16, 1938.
a b c In the autumn of 1939, it was called to my attention that Fig. 24. Ventral side of outer- some Anna Hummingbirds, presumably immature males, were most (a) and next to outer- executing the dives but were not producing the note. I have since most (6) tail feathers of adult watched the performance, and, although the dives were usually male Anna Hummingbird; c, not as steep as those of the adult male, some of them should have outermost feather of juvenal produced the note had the character of the dive alone been remale. All from left side of tail. sponsible for its production. To ascertain if the absence of the note might be due to lack of properly shaped outer tail feathers, museum specimens were examined. It was found that the outer tail feathers of juvenal males are broader, especially toward the tip, than those of the adult (fig. 24), and have a softer vane. I was unable to produce the note with these feathers on the bamboo whip.
Thus, the note at the bottom of the dive of the adult male Anna Hummingbird is apparently produced by the vibration of the outer tail feathers, and although young males still in juvenal plumage may execute the dive, their outer tail feathers are not fitted to attain the vibrations necessary to produce the note.
Thomas L. Rodgers
Museum of Vertebrate Zoology, Berkeley, California, October 21, 1939
