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 island's bird fauna. He noted that the song and call of the resident junco, Junco (hyemalis?) insularis, differed from that of mainland populations of J. hyemalis. He suggested that the song resembled somewhat the trill of the Chipping Sparrow (Spizella 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.
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