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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 congeners, V. annabellaand 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.