title: Sampling effects on the identification of roadkill hotspots: Implications for survey design.
abstract: Although locating wildlife roadkill hotspots is essential to mitigate road impacts, the influence of study design on hotspot identification remains uncertain. We evaluated how sampling frequency affects the accuracy of hotspot identification, using a dataset of vertebrate roadkills (n = 4427) recorded over a year of daily surveys along 37 km of roads. "True" hotspots were identified using this baseline dataset, as the 500-m segments where the number of road-killed vertebrates exceeded the upper 95% confidence limit of the mean, assuming a Poisson distribution of road-kills per segment. "Estimated" hotspots were identified likewise, using datasets representing progressively lower sampling frequencies, which were produced by extracting data from the baseline dataset at appropriate time intervals (1-30 days). Overall, 24.3% of segments were "true" hotspots, concentrating 40.4% of roadkills. For different groups, "true" hotspots accounted from 6.8% (bats) to 29.7% (small birds) of road segments, concentrating from <40% (frogs and toads, snakes) to >60% (lizards, lagomorphs, carnivores) of roadkills. Spatial congruence between "true" and "estimated" hotspots declined rapidly with increasing time interval between surveys, due primarily to increasing false negatives (i.e., missing "true" hotspots). There were also false positives (i.e., wrong "estimated" hotspots), particularly at low sampling frequencies. Spatial accuracy decay with increasing time interval between surveys was higher for smaller-bodied (amphibians, reptiles, small birds, small mammals) than for larger-bodied species (birds of prey, hedgehogs, lagomorphs, carnivores). Results suggest that widely used surveys at weekly or longer intervals may produce poor estimates of roadkill hotspots, particularly for small-bodied species. Surveying daily or at two-day intervals may be required to achieve high accuracy in hotspot identification for multiple species.
authors.affiliation: Conservation Biology Lab (UBC), Research Center in Biodiversity and Genetic Resources (CIBIO-UE), Pole of Évora, Research Group in Applied Ecology, University of Évora, Department of Biology, Mitra, 7002-554 Évora, Portugal. Electronic address: saramlsantos@yahoo.com.
authors.forename: Sara M
authors.initials: SM
authors.lastname: Santos
authors.affiliation: Conservation Biology Lab (UBC), Research Center in Biodiversity and Genetic Resources (CIBIO-UE), Pole of Évora, Research Group in Applied Ecology, University of Évora, Department of Biology, Mitra, 7002-554 Évora, Portugal; Centre for Environmental Biology (CBA), Faculty of Sciences, University of Lisbon, Campo Grande, 1749-016 Lisboa, Portugal. Electronic address: jtiagomarques@gmail.com.
authors.forename: J Tiago
authors.initials: JT
authors.lastname: Marques
authors.affiliation: Research Center in Biodiversity and Genetic Resources (CIBIO), University of Porto, Campus Agrário de Vairão, 4485-661 Vairão, Portugal. Electronic address: andrelourenco300@gmail.com.
authors.forename: André
authors.initials: A
authors.lastname: Lourenço
authors.affiliation: Conservation Biology Lab (UBC), Research Center in Biodiversity and Genetic Resources (CIBIO-UE), Pole of Évora, Research Group in Applied Ecology, University of Évora, Department of Biology, Mitra, 7002-554 Évora, Portugal. Electronic address: denimedinas@gmail.com.
authors.forename: Denis
authors.initials: D
authors.lastname: Medinas
authors.affiliation: Research Center in Biodiversity and Genetic Resources (CIBIO-UE), Pole of Évora, Research Group in Climate Change and Biodiversity, University of Évora, 7004-890 Évora, Portugal. Electronic address: barbosa@uevora.pt.
authors.forename: A Márcia
authors.initials: AM
authors.lastname: Barbosa
authors.affiliation: EDP Biodiversity Chair, CIBIO - Research Center in Biodiversity and Genetic Resources, University of Porto, Campus Agrário de Vairão, Rua Padre Armando Quintas, 4485-661 Vairão, Portugal. Electronic address: pbeja@cibio.up.pt.
authors.forename: Pedro
authors.initials: P
authors.lastname: Beja
authors.affiliation: Conservation Biology Lab (UBC), Research Center in Biodiversity and Genetic Resources (CIBIO-UE), Pole of Évora, Research Group in Applied Ecology, University of Évora, Department of Biology, Mitra, 7002-554 Évora, Portugal. Electronic address: amira@uevora.pt.
authors.forename: António
authors.initials: A
authors.lastname: Mira
mesh_terms: D000663:Amphibians; D000818:Animals; D000835:Animals, Wild; D001717:Birds; D004784:Environmental Monitoring / Q000379:methods*; D008322:Mammals; D018986:Motor Vehicles; D011174:Portugal; D012104:Reptiles; D011795:Surveys and Questionnaires
keywords: Monitoring; Sampling design; Spatial accuracy; Wildlife road mortality