Carcass persistence and detectability : reducing the uncertainty surrounding wildlife-vehicle collision surveys

Carcass persistence time and detectability are two main sources of uncertainty on roadkill surveys. In this study, we evaluate the influence of these uncertainties on roadkill surveys and estimates. To estimate carcass persistence time, three observers (including the driver) surveyed 114km by car on a monthly basis for two years, searching for wildlife-vehicle collisions (WVC). Each survey consisted of five consecutive days. To estimate carcass detectability, we randomly selected stretches of 500m to be also surveyed on foot by two other observers (total 292 walked stretches, 146 km walked). We expected that body size of the carcass, road type, presence of scavengers and weather conditions to be the main drivers influencing the carcass persistence times, but their relative importance was unknown. We also expected detectability to be highly dependent on body size. Overall, we recorded low median persistence times (one day) and low detectability (<10%) for all vertebrates. The results indicate that body size and landscape cover (as a surrogate of scavengers' presence) are the major drivers of carcass persistence. Detectability was lower for animals with body mass less than 100g when compared to carcass with higher body mass. We estimated that our recorded mortality rates underestimated actual values of mortality by 2±10 fold. Although persistence times were similar to previous studies, the detectability rates here described are very different from previous studies. The results suggest that detectability is the main source of bias across WVC studies. Therefore, more than persistence times, studies should carefully account for differing detectability when comparing WVC studies

Reproductive biology and food habits of the swamp racer Mastigodryas bifossatus from southeastern South America

The swamp racer Mastigodryas bifossatus is a large colubrid snake distributed mainly in open areas in South America. Dissection of 242 specimens provided data on body sizes, sexual size dimorphism, reproductive cycles and food habits of this species. Adult M. bifossatus average approximately 1100 mm in snout-vent length, with males and females attaining similar sizes. Reproductive cycles in females seem to be continuous, although oviductal eggs occur mainly from the beginning to the middle of the rainy season with peak recruitment at the end of the rainy season. Clutch size ranges from four to 24 and each newborn individual is about 300 mm SVL. Mastigodryas bifossatus is euryphagic, feeding mainly on frogs (44%) and mammals (32%). Lizards (16%), birds (4%) and snakes (4%) form the remaining prey. Relatively small prey (0.05-0.019) are ingested by adults, and juveniles eat mammals, which suggests that there is no ontogenetic shift in the diet of this snake. Swamp racers forage by day on the ground in open areas but may use arboreal substrates for sleeping or basking.17210410