29(1-2):1-10, 1990(91) 1 Journal of Research on the Lepidoptera 29(1-2):1-10, 1990(91) Hilltopping by the Red Admiral Butterfly: Mate Searching Alongside Congeners William D. Brown * and John Alcock Department of Zoology, Arizona State University, Tempe, AZ 85287-1501 Abstract. Males of the red admiral butterfly Vanessa atalanta (Nymphalidae) establish and defend territories in the late afternoon on a central Arizona hilltop. Resident males engage conspecific rivals in lengthy chases but respond less aggressively toward males of 3 congeneric species. A comparison between V. atalanta and 2 conge- ners, V. annabella and V. cardui, shows that the degree of site tenacity is correlated with the density of rivals. Males of V. annabella, the least abundant species, are most site tenacious, as measured by mean duration of residency and frequency of return to the peak. In contrast, males of V. cardui experience the highest hilltop densities and are the most ephemeral. Males of V. atalanta occur in intermediate density and exhibit intermediate site tenacity. Although male V. atalanta readily respond to any flying insect, the duration and complexity of these interactions is reduced. The various species also express different perch site preferences, which may aid in reducing the frequency of non-productive congeneric encounters. INTRODUCTION Hilltops serve as mate-encounter sites for a striking array of insects (Alcock, 1987; Shields, 1967). In many cases, including the red admiral butterfly (Vanessa atalanta), males perch along ridges and atop peaks where there is no concentration of resources useful to females (Alcock, 1984, 1987; Dimock, 1978; Shields 1967). Possibly hilltops act as orientation guides or dispersal barriers for species in which receptive females are otherwise evenly or diffusely distributed in the environ- ment. In some regions, however, hilltops are unavailable and so male Vanessa butterflies adjust their mate-searching tactics by using alter- native landmarks as territory centers (Alcock & Gwynne, 1988; Bitzer & Shaw, 1979; Palm, 1980). Where hilltops are absent, both V. atalanta and an Australian congener, V. kershawi, use landscape features such as sidewalks and forest clearings as points at which to search for mates. Thus, regardless of the local terrain, Vanessa butterflies appear to establish territories at places that are topographically distinctive. Although different species of Vanessa have been reported to co-occur at hilltops (Dimock 1978; Shields 1967), little is known of the influence congeners may have on their mating systems. Here we report that V. atalanta interacts with other species of Vanessa (annabella, cardui and virginiensis) at a central Arizona hilltop. We describe the hilltopping behavior of male V. atalanta at this site with special attention to the *Present address: Department of Zoology, Erindale College, University of Toronto, Mississauga, Ontario L5L 1C6, Canada