Song Divergence in Hummingbird and Junco Populations on Guadalupe Island

Abstract

Guadalupe Island is a true oceanic island of volcanic origin, lying about 240 km west of Baja California, Mexico.W. E. Bryant (1887) was the first naturalist to make a thorough survey of the islands bird fauna.He noted that the song and call of the resident junco, Bunco (hyemalis?)insularis, differed from that of mainland populations of J. hyemalis.He suggested that the song resembled somewhat the trill of the Chipping Sparrow (Spixella passerina).Bryant also collected Anna Hummingbirds (Calypte anna), but did not comment on the song of this species.Howell and Cade (1954) reported that juncos sang frequently during their visit to Guadalupe Island in June 1953, but they did not hear the slow trilling characteristic of mainland populations of J. hyemalis.They also noted that the call and song of both adult and immature Anna Hummingbirds sounded different from those of mainland individuals and suggested, "It is possible that the small insular population does have an established vocal difference, but future observations will be needed to substantiate this."In this paper I document this insular divergence for both the junco and the Anna Hummingbird. MATERIALS AND METHODSI spent 17 days on Guadalupe Island between 23 November and 26 December 1973.Songs of the island juncos and hummingbirds were recorded between 3-10 December among the wild tobacco (Nicotiuna glauca) groves at the northeast anchorage.A Uher 4000-L tape recorder was used at a tape speed of 19 cm/set with a Uher M514 microphone mounted at the focal point of a 24-inch parabolic reflector.In the laboratory, permanent graphic recordings were made with a Sona-Granh 6061-B audio-frequency analyzer using the wide-band filter.Recordings of Anna Hummingbird vocalizations also were made on the campus of the University of California at Los Angeles for comparison.