Spatial capture-recapture design and modelling for the study of small mammals

Abstract

Spatial capture-recapture modelling (SCR) is a powerful analytical tool to estimate density and derive information on space use and behaviour of elusive animals. Yet, SCR has been seldom applied to the study of ecologically keystone small mammals. Here we highlight its potential and requirements with a case study on common voles (Microtus arvalis). First, we address mortality associated with live-trapping, which can be high in small mammals, and must be kept minimal. We designed and tested a nest box coupled with a classic Sherman trap and show that it allows a 5-fold reduction of mortality in traps. Second, we address the need to adjust the trapping grid to the individual home range to maximize spatial recaptures. In May-June 2016, we captured and tagged with transponders 227 voles in a 1.2-ha area during two monthly sessions. Using a Bayesian SCR with a multinomial approach, we estimated: (1) the baseline detection rate and investigated variation according to sex, time or behaviour (aversion/attraction after a previous capture); (2) the parameter sigma that describes how detection probability declines as a function of the distance to an individual´s activity centre, and investigated variation according to sex; and (3) density and population sex-ratio. We show that reducing the maximum distance between traps from 12 to 9.6m doubled spatial recaptures and improved model predictions. Baseline detection rate increased over time (after overcoming a likely aversion to entering new odourless traps) and was greater for females than males in June. The sigma parameter of males was twice that of females, indicating larger home ranges. Density estimates were of 142.92±38.50 and 168.25±15.79 voles/ha in May and June, respectively, with 2–3 times more females than males. We highlight the potential and broad applicability that SCR offers and provide specific recommendations for using it to study small mammals like voles.

Numerical response of a mammalian specialist predator to multiple prey dynamics in Mediterranean farmlands

“…Each trap was baited with apple or carrot, which provide both food and water for trapped rodents. When the temperatures were low (autumn and winter), hydrophobic cotton was provided inside traps to increase survival (see Romairone et al 2018). Traps were set up in the morning, inspected after 24 h, and subsequently removed.…”

Investigating effects of soil chemicals on density of small mammal bioindicators using spatial capture-recapture models

“…The lack of support for species-specific variation in either g 0 or σ strongly indicates that our density estimates were representative of a Peromyscus community that was comprised of multiple species with comparable space use and detectability [ 80 ]. We also found no evidence that g 0 or σ differed between the sexes, though we acknowledge the short survey duration that resulted in a relatively small number of sex-specific spatial recaptures may have contributed to this result [ 69 , 82 , 85 ]. Nevertheless, our estimated community density was similar to other spatially explicit estimates for Peromyscus in locales where environmental contamination was not a known issue [ 78 , 96 , 98 ].…”

“…A likelihood estimator for single-catch traps has not been developed yet (but see Distiller and Borchers [ 68 ]), but Efford et al [ 67 ] found that modeling single-catch traps as multi-catch can produce unbiased estimates of density if trap saturation is <86%. Therefore, after calculating trap saturation, or the average proportion of traps that were occupied at the end of each occasion, we modeled traps as multi-catch via a multinomial observation model [ 32 , 67 , 69 ]. Recaptures of multiple individuals occurred in traps that were located on >1 sampling grid (i.e., cross-grid captures), effectively constituting a pseudo-clustered sampling design; therefore, we collapsed the grid-specific capture histories into a single study area capture history with five occasions [ 41 , 70 , 71 ].…”

Patterns of Flea Infestation in Rodents and Insectivores From Intensified Agro-ecosystems, Nw Spain

“…However, this pattern was not found in M. arvalis. The colonial lifestyle [58] and the aggressive behaviour of female voles [59] could increase the horizontal transmission in females, balancing the ea burden between male and female voles. However, male voles usually hosted the less frequent ea species; their higher mobility [58] may provoke the encountering with more diversity of ea species.…”