Padrões espaço-temporais de atropelamentos da serpente Helicops infrataeniatus (Squamata, Dipsadidae) em rodovias do sul do Brasil

Abstract

The estimate of fauna mortality from road-kill in just a dozen countries is higher than 400 million individuals per year. Understanding the spatial and temporal patterns of road-kill is important for their mitigation. There are notable advances in the production and adaptation of tools to answer where, when, and how many individuals are killed by cars. Due to the complexity of obtaining sample sufficiency, these patterns are poorly studied at the species level and the literature that explores interannual changes and variations between populations is non-existent. In view of these uncertainties, it is common to assume that the road-kill patterns are similar between years, roads and even between species, reducing the effectiveness of the mitigating measure. We studied spatio-temporal variations in road-kill using the snake Helicops infrataeniatus as a model organism. We studied the annual changes in hotspots, hot moments, and the number of road-kill over the years and between three roads on the coastal plain of southern Brazil. We also explored the influence of the spatial scale and the sampling effort in detecting hotspots over the years, as well as measuring the synchrony of roadkill between roads. The number of road-kill was estimated including searcher efficiency and carcass persistence. We found that hotspots, hot moments, and mortality estimates correspond to the expected patterns of dispersion, activity, and abundance of the species. However, road-kill patterns can change over the years and differ between roads. The location of hotspots over the years varies less with larger scales and with yearly increases in sampling effort, and not necessarily with sample size. Our highest mortality estimate was on BR-392 (53 km), with 61 road-kill/km/year. However, this number can be five times higher if we consider that the impact is concentrated in a 10 km stretch of the Canal São Gonçalo floodplain. We found a biennial pattern in the number of road-kill on one road. It is possible that the variations in road-kill patterns are related to environmental or behavioral changes on a local scale and for short periods. In this sense, it is important to direct efforts to identify the cause-effect of changes in mortality patterns. However, the inherent complexity presents considerable challenges. Thus, we recommend that decision makers implement monitoring efforts and evaluation scales that include the potential spatio-temporal variations of the studied taxon in the identification and mitigation of road-kill patterns.