Assessing precision and requirements of three methods to estimate roe deer density

Abstract

Roe deer (Capreolus capreolus) is the most abundant cervid in Europe and, as such, has a considerable impact over several human activities. Accurate roe deer population size estimates are useful to ensure their proper management. We tested 3 methods for estimating roe deer abundance (drive counts, pellet-group counts, and camera trapping) during two consecutive years (2012 and 2013) in the Apennines (Italy) in order to assess their precision and applicability. During the study period, population density estimates were: drive counts 21.89±12.74 roe deer/km2 and pellet-group counts 18.74±2.31 roe deer/km2 in 2012; drive counts 19.32±11.12 roe deer/km2 and camera trapping 29.05±7.48 roe deer/km2 in 2013. Precision of the density estimates differed widely among the 3 methods, with coefficients of variation ranging from 12% (pellet-group counts) to 58% (drive counts). Drive counts represented the most demanding method on account of the higher number of operators involved. Pellet-group counts yielded the most precise results and required a smaller number of operators, though the sampling effort was considerable. When compared to the other two methods, camera trapping resulted in an intermediate level of precision and required the lowest sampling effort. We also discussed field protocols of each method, considering that volunteers, rather than technicians, will more likely be appointed for these tasks in the near future. For this reason, we strongly suggest that for each method managers of population density monitoring projects take into account ease of use as well as the quality of the results obtained and the resources required.

Recreation and hunting differentially affect deer behaviour and sapling performance

“…Additionally, dropping counts were lower in the vicinity of forest trails than further away, but only when they were open for recreation. Dropping counts are a well‐established proxy for deer space‐use (Acevedo et al 2010, Alves et al 2013, Marcon et al 2019) that allowed us to record long‐term deer space‐use on fine spatial scales over a large area. However, this method does not provide information on deer (foraging) behaviour or absolute density.…”

Sampling scale and season influence the observed relationship between the density of deer and questing Ixodes ricinus nymphs

“…It is also important to consider the methods used, as the counts of deer dung cover a smaller area and do not account for the probability of detection, defecation or decay rates [42]. Although more robust methods to measure deer density, such as distance sampling of deer dung, require more resources, such approaches are important to consider when planning field studies on the effect of deer density on tick populations [51]. Additionally, in cases where resources allow, additional complementary methods could be used to improve accuracy of estimates (e.g.…”

Competitor densities, habitat, and weather: effects on interspecific interactions between wild deer species

“… 2010 ; Marcon et al . 2019 ), and has been used also in our study area (Fattorini et al . 2011 ; Ferretti et al .…”

“…We used pellet group counts, a method that has been consistently used since many decades to estimate deer densities in wooded areas with scarce visibility of animals (e.g. Bailey & Putman 1982;Putman 1984;Mayle 1996;Latham et al 1997;Borkowski 2004;Campbell et al 2004;Acevedo et al 2010;Marcon et al 2019), and has been used also in our study area (Fattorini et al 2011;Ferretti et al 2011bFerretti et al , 2016. We used the fecal accumulation rate technique to avoid potential issues related to the estimate of the decay rates of pellet groups, which vary between habitats (Mayle et al 1999;Campbell et al 2004;see Minder 2006, for our study area).…”