Nebraska Ornithologists' Union
Date of this Version
Brogie & Stage, "MacGillivray's Warbler in Cedar County, Nebraska," from Nebraska Bird Review (June 1987) 55(2).
MacGillivray's Warbler (Oporornis tolmiei) is considered by Johnsgard (1980) to be a rare spring and fall migrant in western Nebraska. with most records from the Panhandle. but reported from as far east as Platte Co. Bray et al (1986) consider it regular and cite a specimen taken in Boone Co.. Whatever the status. this warbler is infrequently encountered in Nebraska. and separating this species from Mourning Warbler (Oporornis philadelphia) can often be difficult. Some authorities believe the two to be conspecific, although Hall (1979) found very few hybrid specimens and Salt (1973) found that they did not respond to the playback of each other's song in the suggested overlap zone in Alberta (Roberson 1980).
It is the authors' opinion that for any record of a MacGillivray's Warbler in central and eastern Nebraska to be entirely convincing the bird should have in-hand data taken on it or extremely well documentation of multiple field marks, which must include tail length in reference to the body. Reasons are as follows: MacGillivray's Warblers are characterized by having a broken eyering, although both male and female, adult and immature, Mouring Warblers may have incomplete eyerings (Wood and Beimborm 1981); while MacGillivray's have black lores and most Mournings have gray lores, some populations of Mourning Warblers are black lored (Robertson 1980). The above mentioned characteristics are not fully explained in any of the major field guides, although they do state that separation and field identification of immatures of these species is often very difficult or next to impossible.
Copyright 1987, Nebraska Ornithologists' Union. Used by permission.