Inter-annual variation in adult demography, but no sex bias in a large lowland population of the threatened Clouded Apollo Parnassius mnemosyne butterfly

Abstract

The Clouded Apollo, Parnassius mnemosyne is a charismatic West Palaearctic butterfly, threatened in some European countries and listed in Appendix IV of the Habitats’ Directive. We investigated a large lowland population of the species inhabiting a complex of irregularly coppiced light forest and adjacent wet meadows in the anthropogenic landscape in the valley of the Narew river in NE Poland. A mark-release-recapture (MRR) method was used over 4 years to estimate population size, adult catchability, daily survival and lifespan. The beginning and length of the flight period (which lasted 4–6 weeks) differed over the years and was clearly related to weather conditions (temperature, sunshine) in April, i.e. the most important period for larval development. The seasonal population size varied from 555 to 942 adults. In contrast to some previous studies, the sex ratio turned out to be well balanced, although the catchability of males was significantly higher than that of females in each year. The quality of the wings deteriorated during the season in both sexes, but it was generally better in the case of females, which indicates that they are less active. Inter-seasonal variation in the lifespan (6.36–12.45 days) is more difficult to interpret, but it is worth noting that individuals lived the longest in the coldest and least sunlit flight period. The temporal fragmentation index (i.e. the ratio of flight-period length to adult lifespan) also varied (3.37–5.97) but was generally relatively low, which suggests that there is no threat of reduction of the effective population size at the moment. Nevertheless, the investigated population may be at risk of decline due to the observed intensification of meadow use and especially the possible conversion of grasslands into cornfields.