The Vocal Apparatus of the Elf Owl and Spotted Screech Owl
The Vocal Apparatus of the Elf Owl and Spotted Screech Owl
In an earlier paper (Condor, 36, 1934, pp. 204-213) on the vocal equipment of North American owls I was unable to consider that extreme pygmy of the bubonid tribe, the Elf Owl (Micropallas whitneyi). Through the efforts of Loye Miller, examination of two syringes of male Elf Owls and correlation with the pitch of their hoots are now possible. As expected, the syrinx is extremely small, but it fits into the series of owls previously studied as a terminal member. The measurements with those of the Pygmy Owl, Glaucidium gnoma, in parentheses for comparison are: length of vibrating membrane, 3.1-3.2 mm. (3.6-3.9) ; length of membrane as per cent of bronchial diameter, 200-206 (206-211) ; bronchial diameter 1.6-1.6 mm. (1.8-1.9) ; tracheal diameter, 2.1 mm. (2.5-3.0).
The pitch of an Elf Owl's hoot or whistle is Ez flat to Ez natural. This is two octaves and a little more above the hoot of male Horned Owls (D). The inverse proportion between membrane length and pitch has been used in computing the theoretical vibration rate of the Elf Owl. The ratio of the membrane to vibration rate in the male Horned Owl was taken as the norm. The computed rate for the Elf Owl is 1158.6 or about Dz natural of the temoered scale which. it will be noted. departs from observations by only half a tone. Thus over the extreme range of size in the owls, structures and notes produced are well correlated. The dependence of hoot on diameter of air passages and this in turn on size of the bird is further borne out (see p. 212, op. cit.).
The muscle attachments of the Elf Owl syrinx are on the seventh bronchial semiring on both sides. This arrangement is not unlike that in other small owls. There is no asymmetry as in Gluucidiu~ and Strix.
The syrinx of a male Spotted Screech Owl (Otus trichopsis) has the insertion of the intrinsic muscles on the eighth right bronchial ring and the seventh left ring, identical with one asymmetrical Otus asio already reported. The measurements are: length of vibrating membrane, 4.4 mm.; length as per cent of bronchial diameter, 209; bronchial diameter, 2.1 mm.; tracheal diameter, 3.6 mm. Compared with males of the small race gilmani of Otus asio these are but slightly smaller. No important difference in pitch should result. Loye Miller reports that he observed no higher pitch in trichopssis. The special characteristic of the Spotted Screech Owl's note is its rhythm, which of course is a matter of nervous control.
Alden H. Miller
Museum of Vertebrate Zoology, Berkeley, California, August 6, 1935
