Predation, thermoregulation, and wing color in pierid butterflies

This paper explores two hypotheses about the relationships among predation, thermoregulation, and wing color in butterflies: First, that butterflies are susceptible to predation during thermally marginal periods (e.g., cool weather) when effective thermoregulation and flight are not possible; second, that Pieris butterflies are relatively unpalatable to visual predators, supporting the idea that the white wing pigment of Pieris represents aposematic coloration. Field experiments with Pieris and Colias in 1984 and 1985 demonstrate that substantial predation may occur during the morning period before butterflies are able to actively fly. Circumstantial evidence is presented to suggest that at least some of the predation is by small, cursorial mammals. Feeding experiments in the field using Grey Jays as predators indicate that Pieris napi and P. occidentalis are less palatable than other sympatric butterflies, including confamial Colias alexandra. These and previous results suggest that Pieris are edible but less preferred as prey by birds, and that the degree of palatibility may vary among Pieris species. The relatively low palatability of these Pieris is consistent with the hypothesis that their white pigmentation represents aposematic coloration; however, the cues by which potential bird predators might discriminate against Pieris have not been established.