Vantage point counts and monitoring roe deer

Abstract

Vantage point counts (VPCs) are adopted to estimate the densities of roe deer (Capreolus capreolus) populations for harvest management. Thus, counts should be performed only within blocks without woodlands where it is possible to relate counts to block sizes. Alternatively, if VPCs are simply carried out on all blocks in a study region, the expectations of total counts could be used as relative abundance indices. In most cases, surveying all blocks is too demanding because of the number of observers required, time, and organization. Therefore, VPCs are performed only on a portion of the blocks, and relative abundance indices are estimated from these counts. If the blocks are selected by means of probabilistic sampling schemes, then statistically sound estimators of total count expectations can be adopted. Therefore, the estimation of the sampling errors, construction of confidence intervals, and assessment of change are possible, together with a post hoc power analysis for evaluating the probability of failing to detect a change in the expectations. Our objective in this study is to consider sampling strategies that allow the performance of all these statistical steps and to check the performance of these strategies on a hunting district located in Tuscany, Italy, in which all the blocks were surveyed in 2013 and 2014. The results provide evidence of the imprecision of the estimators. Even for large sampling fractions of 40-50%, the relative standard errors never decreased below 20%, and the corresponding powers in detecting a change of 30% at a level a ¼ 0:05 were <0.65. Our results highlight the need for efficient and robust alternative strategies. Ó 2017 The Wildlife Society.

Using camera traps to estimate ungulate abundance: a comparison of mark–resight methods

“…That result may have occurred because on Antelope Island, males occur in large groups and in open areas with less rugged terrain compared with females with lambs that are near escape terrain (Whiting et al, 2010). Many factors were logistically difficult, however, when performing ground surveys (Bowler et al, 2019;Zaccaroni et al, 2018). First, one survey typically required one technician working a 9h day to complete.…”

“…By having one surveyor and date-specific surveys, we created the potential for conflicts with weather and work schedules. Additionally, large amounts of planning, organization, time searching for animals and observing marked individuals are challenges associated with this method [e.g., McClintock & White, 2007;Zaccaroni et al, 2018], and bias can occur among surveyors with differing levels of experience (Walter & Hone, 2003). These complications should be considered when planning to use ground surveys to estimate ungulate abundance.…”

“…Two common methods of estimating population abundance for ungulates that can be viewed easily in landscapes with limited vegetation are aerial surveys (Holl et al, 2004;Palmer et al, 2018;Walter & Hone, 2003), and resight surveys performed from the ground (Johnson et al, 2010;McClintock & White, 2007;Zaccaroni et al, 2018). Helicopter surveys have been used increasingly during the past 20 years to produce population estimates of ungulates (Bleich et al, 1994;Krausman & Hervert, 1983;McClintock & White, 2007).…”

Population Estimates and Habitat Selection of White-tailed Deer (Odocoileus virginianus ustus) in the Antisana Water Conservation Area, Ecuador

“…The main criterion for the selection was to find the largest number of deer possible within the 8457 ha reserve. We did not choose locations randomly as the logistics of placing a large number of observers in the field are challenging and expensive 14,15 . Also, highaltitude environments with low levels of oxygen pose additional constraints on intense sampling within a large area 16 .…”

“…Detectability of animals may vary due to weather conditions, nearby agricultural practices, the experience of the observers, and types of vegetation 15,16 . The first day at dawn, for example, fog and rain at most vantage points decreased deer detectability.…”