Road-killed toads as a non-invasive source to study age structure of spring migrating population

Abstract

Development of road system causes worldwide barriers to wildlife movement and leads to mass road mortality which is a serious threat to the biodiversity, especially globally endangered amphibians. Animal carcasses, however, constitute an important non-invasive material for further research including species life history traits, but there is little known whether the road-killed animals are a representative sample of entire population. The aim of our research was to compare the age structures between road-killed and live individuals which crossed the road successfully during the breeding migration. As a model species, we used the common toad Bufo bufo which is a main amphibian traffic victim in Europe. We collected toe clips of dead and live toads during their breeding migration in four sampling sites located in the lowlands of western Poland. Phalanges were used for age determination by the skeletochronology. There were no significant differences in age distribution between live and dead individuals of the same sex in all populations studied. In compared groups, medians and mean ages were the same or differed marginally and confidence intervals for the mean age almost completely overlapped. Our results suggest that toads are killed on roads regardless of individual age, thus skeletochronological analysis of dead individuals is useful to study age structure of a live population. Our approach allows to avoid mutilation of amphibians and can be used to increase the knowledge of age structure of a given species living near the road as well as to study long-term road effect on amphibian demography. However, further comparative research on different species is required.