Territorial behavior of the red admiral,Vanessa atalanta (Lepidoptera: Nymphalidae) I. The role of climatic factors and early interaction frequency on territorial start time

We examined the relative importance of climatic factors and population density to territorial start time ofVanessa atalanta males. Start time varies with solar altitude and therefore with seasons. We removed seasonal effects by converting start times to corresponding solar altitudes. Start time solar altitude correlates primarily with ambient temperature (T _a) and secondarily with substrate temperature (T _s), regardless of cloud cover. Overcast cloud cover resulted in later not earlier start times as expected from reduced solar radiation (R) levels. R may affect start time indirectly by affectingT _s and later start times under overcast skies may be a result ofT _s. Start times under solid overcast but not under broken overcast were different than under clear skies, suggesting thatV. atalanta males can use dim sun or blue patches in broken overcast as a start time cue. Early interaction frequency is correlated withT _a and wind direction, but not with start time itself, suggesting that male population density is unimportant compared with climatic factors. We conclude thatV. atalanta has a climate-dependent start time but, also, that maintaining a relatively fixed daily schedule is more important to males than is achieving an optimal body temperature while perching.