Blue-throated hummingbird song: A pinnacle of nonoscine vocalizations

Auk, The, Jan 2000 by Ficken, Millicent Sigler, Rusch, Kathryn M, Taylor, Sandra J, Powers, Donald R

ABSTRACT.-Little is known about the structure and function of hummingbird vocalizations. We studied the vocalizations of Blue-throated Hummingbirds (Lampornis clemenciae) at two sites in southeastern Arizona. Songs were produced by males and females. Male songs consisted of arrays of notes organized in clusters of "song units." Within sites, all males shared the same song units. Individual differences occurred in some temporal aspects of song, and slight but consistent differences in note structure occurred between the two sites. The organization of units within songs was marked by rigid syntax, and long songs were produced by agglutination of units. Male songs may function in territorial advertisement and mate attraction. Female songs were very different acoustically from those of males and typically were given when females were within a few centimeters of a male. In these situations, the female's song often overlapped temporally with the male's song. Of the hummingbird species studied so far, the Blue-throated Hummingbird has the most complex songs and is the only known species with complex female songs. Blue-throated Hummingbirds show convergence with oscines in vocal complexity, song organization, song function, and possible learning of some song elements. Received 25 june 1998, accepted 10 May 1999.

MOST SPECIES OF HUMMINGBIRDS are characterized by marked plumage dimorphism, polygyny, and lack of paternal care (Schuchmann 1999). Consequently, sexual selection would be expected to exert a strong influence on courtship and agonistic behavior. Although sexual selection plays an important role in the evolution of oscine song (Catchpole and Slater 1995), in hummingbirds attention has focused almost exclusively on visual signals, because many species perform complex display flights (Wagner 1954). Hummingbird vocalizations are sometimes portrayed as mere "squeaks," assessments that probably contribute to lack of interest in detailed analysis of hummingbird sounds. Some recent studies, however, indicate a high degree of vocal complexity, and in some cases vocal learning and dialects (Gaunt et al. 1994).

The Blue-throated Hummingbird (Lampornis clemenciae) inhabits wooded canyons in the Chisos Mountains of Texas, the mountains of southwestern New Mexico and southeastern Arizona, and most of Mexico west of the Yucatan Peninsula. It is the largest hummingbird that breeds in the United States, and males have iridescent blue throats that are absent in females.

In contrast to many North American hummingbirds, aerial courtship displays have not been observed in the Blue-throated Hummingbird (Wagner 1954). Therefore, we anticipated that vocalizations would be particularly important in this species' behavior, perhaps having a dual role of territorial advertisement and mediating interactions with females (i.e. similar to the functions of oscine song). Wagner (1954) distinguished two kinds of vocalizations, songs and calls, and indicated that both are involved in reproductive activities in Bluethroated Hummingbirds. However, no detailed descriptions of vocalizations (and no sonograms) have been published for the species. Wetmore (1932) reported that these hummingbirds often utter "sharp, squeaking calls," and that males have ". . . a simple song of three or four notes, repeated at short intervals . . . ." Blue-throated Hummingbirds have several calls and exaggerated postures and displays associated with agonistic behavior (unpubl. data), but here we deal with vocalizations that may be termed "songs" because of their structural complexity and the contexts in which they are used.

Our objectives include a description of acoustic structure and organization of song, analysis of behaviors associated with singing to assess usage and possible functions of song, and examination of acoustic structure of two populations to determine whether microgeographic differences occur. We also make qualitative comparisons of songs of Blue-throated Hummingbirds with those of other hummingbird species and with oscines.

METHODS

We conducted the study at two sites in Cochise County, southeastern Arizona, that are about 150 krn apart: the Southwestern Research Station (SWRS) in the Chiricahua Mountains, and Ramsey Canyon (RC) in the Huachuca Mountains. Both sites have numerous hummingbird feeders distributed in both clumped and dispersed patterns. Blue-throated Hummingbirds also occur away from feeders, but almost all of our recordings were made within 10 m of feeders. All males from which songs were recorded were actively defending territories. The presence of feeders may have increased the amount of aggression and perhaps singing rates, but feeders probably did not affect the aspects of song that we studied.

We recorded songs of two males at RC in April, one in 1995 and one in 1997. The birds were unmarked but probably were different individuals because of the distance between sites. We recorded sequences of songs from these males over several days after the onset of territorial establishment. Four males were recorded at RC in late August, one in 1995 and three in 1997.