The effects of methodological limitations in the study of butterfly behavior and demography: a daily study of Vanessa atalanta (Lepidoptera: Nymphalidae) for 22 years

Abstract

Normally, butterfly behavior and population size are studied intensively for brief periods or occasionally for long periods, not in detail for long periods, producing an incomplete view in both cases. How time limitation affects studies has been unknown for a long time. This paper analyses this problem based on an intensive long term study of Vanessa atalanta (L.) that covered nearly 8000 days, most of them consecutive, for 22 years (April 15, 1977-April 14, 1999), in a subtropical habitat near Orlando, Florida. There is no evidence that ethological studies are affected by their normally brief duration (one year or less), but the analysis of yearly values hid the associations of number of individuals and arrival time with climate. In small areas, isolated population counts lasting less than two weeks are not reliable, according to this study. We found no difference in number of visitors for El Niño years. The daily number of visitors was inversely correlated with temperature and precipitation, but arrival time of the first visitor was positively correlated with both. The number of visitors reaches a peak near the end of Winter. The activity period span is greater than in more seasonal climates. Individuals were active even at 10° C and with 9 m/s winds. Individuals with fresh wing condition were most common from January to June. There were 82 atypical cases of individuals arriving before 12:00 hr. Aerial interactions were seen whenever there was more than one individual in the site (i.e. 41 % of days, N=7634 total days). Only once in these 22 years was predation seen.