Long-term capture and handling effects on body condition, reproduction and survival in a semi-aquatic mammal

Abstract

In long-term individual-based field studies, several parameters need to be assessed repeatedly to fully understand the potential fitness effects on individuals. Often studies only evaluate capture stress that appears in the immediate weeks or breeding season and even long-term studies fail to evaluate the long-term effects of their capture procedures. We investigated effects of long-term repeated capture and handling of individuals in a large semi-aquatic rodent using more than 20 years of monitoring data from a beaver population in Norway. To investigate the effects, we corrected for ecological factors and analysed the importance of total capture and handling events, years of monitoring and deployment of telemetry devices on measures related to body condition, reproduction and survival of individual beavers. Body mass of dominant individuals decreased considerably with number of capture events (107 g per capture), but we found no statistically clear short or long-term effects of capture and handling on survival or other body condition indices. Annual litter size decreased with increasing number of captures among older individuals. Number of captures furthermore negatively affected reproduction in the beginning of the monitoring, but the effect decreased over the years, indicating habituation to repeated capture and handling. By assessing potential impacts on several fitness-related parameters at multiple times, we can secure the welfare of wild animal populations when planning and executing future conservation studies as well as ensure ecologically reliable research data.

Aquatic habitat use in a semi-aquatic mammal: the Eurasian beaver

“…Territory borders are identified based on scent mound concentrations, sight observations of known patrolling beavers backed up by GPS data. The main river contains ten distinguishable territories inhabited by approximately 32 individuals [33,57]. Predation pressure is low as wolves (Canis lupus) and bears (Ursus arctos) are functionally extinct in the area, and lynx (Lynx lynx) only occur at low densities [84,105].…”

“…The study river is part of a larger monitoring project where beavers in the area have been monitored through an extensive capture programme, the Norwegian Beaver Project (NBP), since 1997 [57]. The long-term monitoring project aims to capture all newcomers (kits and dispersers from outside the study site) annually, enabling identification of individuals at later encounters and family group sizes.…”

“…Beavers are socially monogamous, monomorphic, nocturnal mammals that inhabit various freshwater bodies [38,57]. They live in family groups consisting of the dominant breeding pair, kits of the year, and older non-breeding offspring [33,58,59].…”

“…They live in family groups consisting of the dominant breeding pair, kits of the year, and older non-breeding offspring [33,58,59]. Beavers reach sexual maturity during their second winter [59], and give birth to one to five kits in mid-May at northern latitudes [57]. The kits emerge from the lodge in July when they start feeding on their own [33].…”

“…No clear dietary differences have been found between sexes, ages, or social ranks in beavers [65,69,85], but several studies indicate that foraging behaviour may differ seasonally as territorial movements vary among individuals [86][87][88]. Furthermore, individuals may be affected by various ecological conditions during their lifetime, such as loss and acquisition of territories [15,89], that can affect their behavioural time-budgets and consequently their body condition, reproduction, and survival [57,90].…”