Behav Ecol Sociobiol (1990) 26:421-426 Behavioral Ecology and Sociobiology g Springer-Verlag 1990 Does the "Teer" vocalization deterprospecting female red-winged blackbirds? A speaker-occupation experiment Ken Yasukawa Beloit College, Departmentof Biology, 700 College Street, Beloit, WI 53511, USA ReceivedJuly 19, 1989 / Accepted December 17, 1989 Summary. A speaker-occupation experiment was con- ducted to determine whether female red-winged black- birds (Agelaius phoeniceus) use the aggressive "Teer" vocalization to deterconspecific femalesthat are prosp- ecting for opportunitiesto settle. In each of 14 trials conducted during the breeding seasons of 1987, 1988, and 1989, tape recordings and a pair of loud speakers were used to "defend" suitable habitat. Observations of female red-winged blackbirds settling on these "speaker territories" and on adjacent control areas showed that speaker territories were settledsignificantly earlier than silentcontrol territories. Each of the 14 first settlers on speaker territories included at least one speak- er location within the bird's display area, and 9 of the 14 included both speaker locations. Additionalobserva- tions showed that the rate at which prospecting females visited control and speakerterritories, and the number of femaleseventually settlingon them, were not signifi- cantly different. Finally, femalesthat settled on speaker territories sang Teers at significantly higher rates than those on control territories. These results demonstrate that the Teeralone was not sufficient to deterprospect- ing female red-winged blackbirds. On the contrary, Teers given in the absenceof an actual resident may have at- tracted settlers.It is suggestedthat the aggressive Teer vocalization might functionto establish dominance rela- tionships among the females sharing a polygynous male'sterritory. Introduction The vocal behavior of birdshas been studiedfrequently, and potential functions such as territorydefense and mate attraction have been examined (e.g., Armstrong 1963; Hinde 1969;Nottebohm 1975;Payne 1983).Most studiesof avianvocal behavior have focusedon the sing- ing of males, but females of many species also vocalize (e.g., Armstrong 1963; Ritchison 1983, 1986; Arcese et al. 1988). In some species, such as the red-winged blackbird (Agelaius phoeniceus), the repertoire of the fe- male includes a vocalization that is given during aggres- sive interactions with other females.Such aggressive in- teractions could representa resident female's attempt to deterpotentialintruders, and the aggressive vocaliza- tions of females thus potentially function in territory defense. Territoriality is characterized by advertising behavior and overt attempts by residentsto maintain exclusive access to their defended areas (see Searcy 1986). Male red-winged blackbirds are well-known for theirterritori- al behavior,which includesvocal advertisement, visual display, and overtdefense (Nero 1956b;Orians and Chr- istman1968; Peek 1972; Smith1972, 1976, 1979).Sever- al authors have noted the similarity between the territory defense behavior of males and the aggressive behavior of females,and have proposedthat the femalessharing a polygynousmale'sterritory partition it into non-over- lapping "subterritories",which they defend against other females(Nero 1956a, b; Orians 1961, 1980; Case and Hewitt 1963; Wiens 1965; Orians and Christman 1968; Wittenberger 1979; Lenington 1980; Beletsky 1983a, b, c; Hurlyand Robertson1984). Severalobservations supportthe hypothesis that fe- male red-winged blackbirds defend "subterritories" within the territories of their mates. Femalered-winged blackbirds displaytowardand attackconspecific female intruders(Nero and Emlen 1951; Nero 1956b; Len- ington 1980; Searcy 1986), and they attack taxidermic mounts of female red-wingedblackbirdsplaced near their nests (LaPradeand Graves 1982; Yasukawaand Searcy1982; Searcy1986, 1988). Several observations are also consistent with the hy- pothesis that female red-winged blackbirds vocally de- fend "subterritories".Female red-winged blackbirds have severalvocalizations, most of which are short and simple, and signal general arousal or agitation (Nero 1956a, b; Oriansand Christman 1968).The "Teer"vo- calization (Hurly and Robertson1984),however, is loud and structurally complex (see Beletsky 1983a; Fig. 1B, C) and is given by resident females during aggressive