Effects of a paved road on mortality and mobility of red bellied toads (Melanophryniscus sp.) in Argentinean grasslands

Abstract

Melanophryniscus sp. is an endemic toad restricted to Sierra de la Ventana, in the Argentine Pampas. Part of its reproductive habitat is crossed by a paved road. We studied the effects of the road on the mortality and mobility of the toads. During the days following rain, we surveyed transects on both sides of the road, capturing, photographing and immediately releasing each toad. Population size in the area was estimated in 1074 individuals (871 to 1363, 95% CI) by means of mark-recapture analysis. We found fifteen individuals killed by vehicles in the 2003-04 and ten in the 2004-05 reproductive seasons. This mortality represents from 2.5 to 5.9% of the population annually, considering that 73% of the mortality period was sampled and a detection rate of dead frogs of 40%. Other factors associated to roadside habitat, such as rapid drying of roadside ditches, maintenance work, increased frequency of fire, pollution by gas, oil and fuel emissions and losses from vehicles, and poaching as pets by tourists, may also reduce the survival of the toads. We recorded capture sites and calculated the average distance between captures as 33.04 m for males and 22.50 m for females. Only two of the 76 observations of recaptured toads were made on the opposite side of the road. Roads can be considered as having a significant impact on this species by augmenting mortality, hindering the mobility of the species and increasing habitat isolation.