Costeffective nocturnal distance sampling for lan

Authors: Valentina La Morgia Roberta Calmanti Alessandro Calabrese Stefano Focardi

Publish Date: 2015/01/13

Volume: 61, Issue: 2, Pages: 285-298

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Abstract

Estimating the size of ungulate populations dwelling forested habitats is technically difficult and expensive In particular population assessment via conventional distance sampling CDS at landscape scales is challenging and often discarded for its high costs The development of a framework for its methodological optimization is mandatory To tackle this issue we used survey simulations For arbitrarydistributed populations we compared the following i systematic random transect allocation ii random selection of footpaths and iii twostage sampling selection of footpaths 2 5 10 blocks The performance of twostage sampling and random footpath selection estimators was similar Then we applied previous results to estimate the size of a red deer Cervus elaphus population in the Italian Apennines Using data from a pilot survey we estimated density via CDS and density surface modeling DSM and we quantified survey costs per unit effort Considering our deer distribution we finally simulated and evaluated the costeffectiveness of the abovementioned designs for a range of realistic efforts 25–65 transects CDS produced a negatively biased and less precise estimate than the corresponding DSM For an effort of 65 transects design ii estimates were unbiased coefficient of variation = 031 while design iii provided negatively biased estimates coefficient of variation = 027 Twostage sampling designs with few blocks were less expensive than other designs in attaining the same level of precision and they emerged as a costeffective survey design Our simulation approach thus provided managers a readily available tool to improve the estimate of ungulate abundances at a landscape scaleThanks are due to A Gennai Foreste Casentinesi Natural Park for the logistic support during field activities and to O Friard University of Turin for his informatic support Two anonymous referees provided very relevant comments to the manuscript

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