The spatial distribution of animal casualties within a road corridor: Implications for roadkill monitoring in the southern Iberian rangelands

Abstract

We assessed wildlife roadkill spatial patterns focusing on asphalt roads in southern Spanish oak rangelands (“dehesas”). Four roads in the Sierra Morena range (Andalusia) were surveyed twice during autumn-winter 2009–2010 and spring-summer 2010. Roadsides were walked on both sides across the total road length (53 km; overall length walked per season = 106 km) for each field season by 1–4 trained observers at ∼1–2 km/h. Asphalt surface, road verges/shoulders, runoff ditches and road banks/slopes (neighboring habitat) were exhaustively inspected for all dead vertebrates, which were georeferenced and identified. Roadkills (N = 396) were classified into 67 species (5 amphibians, 7 reptiles, 37 birds and 18 mammals). In total, 128 (32.3%) of all roadkills were found within the road asphalt lanes, with the remaining two-thirds (268, 67.7%) outside the asphalt lanes. This pattern was consistent regardless of season and several structural attributes of roads. However, vertebrate class was determinant, with more poiquilotherms (amphibians and reptiles) being detected inside asphalt compared to birds and mammals (off-asphalt casualties were significantly more numerous). This is a strong argument in favor of recommending surveying roadkill on foot as a main survey method or complementarily to vehicle surveys.