Hybridization in Buntings (Passerina) in North Dakota and Eastern Montana

Abstract

THE Indigo and Lazuli Buntings (Passerina cyanea and P. amoena) are closely related complementary species that breed chiefly in the eastern half and western half, respectively, of the contiguous United States. Their breeding ranges overlap in the southern Great Plains, and hybrid-ization there has been described by Sibley and Short (1959) from southern Nebraska and northeastern Colorado through the western two-thirds of South Dakota. This present study extends documentation of hybridization northward into North Dakota and eastern Montana, and discusses the identification of hybrid characteristics in buntings. Phenotypic characteristics of specimens from extreme eastern and western United States are described and compared with those from the overlap area to elucidate variations resulting from hybridization. The term hybridization as used in this paper is defined broadly as interbreeding between individuals of morphologically and genetically distinct populations and also interbreeding between hybrids and pures or between hybrids. Thus a hybrid could be F1 (Indigo X Lazuli), a backcross (F1 x Indigo or F1 X Lazuli), or a specimen representing any combination of Indigo and Lazuli genes. Both species occur around brushy vegetation along the edges of woodlands. Their songs and calls, general behavior, and nests and eggs are similar. Songs of the two species differ slightly, that of the Lazuli being approximately one and one-half times as fast as the song of the Indigo (Thompson 1969). In North Dakota the Lazuli's song seems to be more choppy and shorter-i to 2 sec vs. 2 to 3 sec in the Indigo. In a fewcases I noted atypical songs that turned out to be from obviously hybrid specimens. Recently male Indigos have been recorded quite often west to the Pacific coast-in California: May 1950 (Cardiff 1951), June 1956 and 1957 (Bleitz 1958), February 1959 (Williams 1961), January 1963 (Wilbur 1963); in Washington: same bird in June and July 1958 (Calder 1966); and in Nevada: June 1940 and 1951 (Richardson 1952). Sibley and Short (1959) listed more western records including the western Great Plains. In addition, Audubon Field Notes contains several Indigo records in the far west. Lazulis have apparently been much less frequent in eastern localities, and I know of no Lazuli records east of the Mississippi River.