Selasphorus Sasin Research Articles

Neuromuscular mechanisms of wing beat in hummingbirds

1. The neuromuscular mechanism of the pectoral muscle (M. pectoralis major) was analysed by recording impulse discharges and tension developments of the muscle in hummingbirds (Calypte costae, Selasphorus sasin andCalypte anna). 2. Bursts of impulse discharges were observed from the whole pectoral muscle for each wing beat during the flight movements. 3. The frequency of burst discharge i.e., that of the wing beat is fairly constant (35–45 c.p.s.) and is identical in the hovering type of flight and the fast locomotive flight. 4. The amplitude of the wing beat is variable, it is higher during fast locomotive flights and it increases during acceleration of locomotion. 5. The amplitude of wing beat is altered by increasing the number of active motor units within the muscle and by increasing the number of impulses arriving at each motor unit for each wing beat. 6. The contraction of the pectoral muscle is a “twitch” per wing beat during the hovering flight but it becomes a “tetanus” of 2–5 motor impulses of a high frequency (300–500 c.p.s.) during the locomotive flight or acceleration of locomotion. The tetanus is no longer than the twitch but only higher in amplitude. 7. The contraction time of the pectoral muscle is about 8 msec and the tetanus fusion frequency is 250–300 c.p.s. at a body temperature of 40°C. 8. Similar experiments performed with the finch (Taeniopygia castanotis) show a similar constancy of the wing beat frequency (22–25 c.p.s.), contraction time of about 14 msec (40°C) and tetanus fusion frequency of 100–150 c.p.s.

Trochilidae or Humming-birds brought in our Country

There are many Japanese who have heard the word "Humming-bird", but few have seen a live one and even the stuffed specimens were not seen by many people. Humming-birds were imported into Japan only twice before the Pacific War. The first person who bred the hummer was Mr. Rihee Okada, the aviculturist in Itami, Hyôgo Pref. while the second was Yamashina, the senior author. Thirteen humming-birds were brought into Japan in four groups across the Pacific by Mr. E.Kinsey, the bird-fancier in San Francisco. The species then imported were the Anna Humming-bird Calypte anna and the Allen Humming-bird Selasphorus sasin both of which inhabit the United States. One male of the former and a pair of the latter were the first to come to Japan on April 9, 1937 and the rest of them arrived one after the other in the following twelve months. Afterwards a pair of the Anna Humming-birds selected from among them were presented by the senior author to the Zoological Garden at Uéno, Tokyo. Here the first time in our country the live humming-birds were exhibited to the public to the great wonder of many Japanese, but unfortunately in a week they were found missing.On March 16, 1955 eight hummers from Brazil were brought in Japan and several of them were exhibited to the public in Uéno Zoo. It is said that those birds were the gift of a Japanese living there. Since those hummers were the first ones to arrive in this country after the war, they became a great topic among those who are fond of birds and animals. One of them represents Anthracothorax viridigula and the rest of them seem to be Eupetomena macroura.The senior author was so enthusiastic about keeping the hummers alive that one of the Anna Humming-birds lived for three years and nine months and one of the Allen Humming-birds for exactly four years both of which are the highest records of humming-bird breeding in Japan.One hummer sent to Mr. Okada from the U. S. A. died in a week, but the specific name of which is unknown.

Ecologic Overlap and Interspecific Strife in Breeding Population of Anna and Allen Hummingbirds

Analyses of interspecific competition in natural populations are fundamental to modern theory in ecology and evolution. Yet, at least among higher vertebrates, few examples with supporting details are on record, and current theories require corroboration in the field (Errington 1946; Crombie 1947; Richards 1948; Lack 1949). This will come slowly, chiefly because the proper recording and interpretation of competitive incidents in the field require a long and intimate field acquaintance with a given species and because the details of such incidents are often elusive or subtle. Also, the true nature of adaptive differences between closely similar species may escape detection unless these are observed in competition (Lack 1944; Crombie 1947). The object of this paper is to examine ecological differences between two sympatric species of hummingbirds which overlap in both geographic and habitat distribution, providing an example of what, in Schmalhausen's (1949) classification of competitive situations, is termed active intergroup competition. The Anna hummingbird (Calypte anna) and the Allen hummingbird (Selasphorus sasin, formerly S. alleni) are almost restrictedly Californian in breeding distribution, and their breeding ranges overlap along the coast from the San Francisco Bay region to Ventura County (Grinnell and Miller 1944). The evidence to be presented here was obtained in the course of a five-year census, in the period from 1943 to 1947, of the breeding population of hummingbirds in Woolsey Canyon, which drains into Strawberry Creek on the west side of the Berkeley Hills. The study area, now a part of the University of California campus, totals about 125 acres and, until 1948, supported a complex of woodland and chaparral vegetation surrounded by open grassy slopes such as typically fills the canyons in the central Coast Ranges (see Fig. 1). Studies of territoriality in hummingbirds reported earlier (Pitelka 1942) have been continued, and while data presented in this paper concern specifically the populations of Woolsey Canyon, much original information on behavior to be reported elsewhere has been used in interpreting the data on these populations.