Hot spots and hot moments of diamondback terrapin road‐crossing activity

Abstract

Summary Road mortality is a major component of human impacts on wildlife populations, and the pervasiveness of roads on the landscape presents a substantial challenge for managing those impacts. The feasibility of methods to reduce road mortality depends on the degree to which this threat is spatially or temporally concentrated, which can be based on habitat, human activities or species' ecology. Diamondback terrapins Malaclemys terrapin are a species of conservation concern across their range, and road mortality is a major threat contributing to local population declines. We used intensive road surveys of the 8·7‐km Downing‐Musgrove Causeway to Jekyll Island, Georgia, USA, over 2 years to determine whether road activity and mortality was diffused or concentrated spatially (hot spots) or temporally (hot moments) in order to guide efficient management. In 2009 and 2010, we documented 636 terrapin crossings that were temporally and spatially condensed. Temporally, there was a 70–80% chance of a terrapin occurring on the road within a 3‐h period around the diurnal high tide and within the first 30 days of the ˜75 day nesting season. Over the two nesting seasons, 52% of terrapin occurrences on the road occurred within the 3‐h period around high tide. Spatially, 30% of terrapins were observed crossing in three hot spots that composed less than 10% of the length of the entire causeway, and the percentage of unvegetated high marsh was negatively associated with the number of terrapins that occurred on a section of road. Synthesis and applications. Our results demonstrate that hot spots and hot moments can be identified for species at finer scales than those found by other studies and are related, strongly or weakly, to specific temporal processes or habitat features. We found patterns of road mortality, like most threats, can be diffused or concentrated; therefore, complementary management tools that focus on hot spots or moments and also address the more diffused component of road mortality will be required to reduce this threat for at‐risk wildlife.