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- Avoiding verisimilitude when modelling ecological responses to climate change: the influence of weather conditions on trapping efficiency in European badgers (Meles meles)
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The signal for climate change effects can be abstruse; consequently, interpretations of evidence must avoid verisimilitude, or else misattribution of causality could compromise policy decisions. Examining climatic effects on wild animal population dynamics requires ability to trap, observe or photograph and to recapture study individuals consistently. In this regard, we use 19 years of data (1994–2012), detailing the life histories on 1179 individual European badgers over 3288 (re-) trapping events, to test whether trapping efficiency was associated with season, weather variables (both contemporaneous and time lagged), body-condition index (BCI) and trapping efficiency (TE). PCA factor loadings demonstrated that TE was affected significantly by temperature and precipitation, as well as time lags in these variables. From multi-model inference, BCI was the principal driver of TE, where badgers in good condition were less likely to be trapped. Our analyses exposed that this was enacted mechanistically via weather variables driving BCI, affecting TE. Notably, the very conditions that militated for poor trapping success have been associated with actual survival and population abundance benefits in badgers. Using these findings to parameterize simulations, projecting best-/worst-case scenario weather conditions and BCI resulted in 8.6% ± 4.9 SD difference in seasonal TE, leading to a potential 55.0% population abundance under-estimation under the worst-case scenario; 38.6% over-estimation under the best case. Interestingly, simulations revealed that while any single trapping session might prove misrepresentative of the true population abundance, due to weather effects, prolonging capture–mark–recapture studies under sub-optimal conditions decreased the accuracy of population estimates significantly. We also use these projection scenarios to explore how weather could impact government-led trapping of badgers in the UK, in relation to TB management. We conclude that population monitoring must be calibrated against the likelihood that weather conditions could be altering trap success directly, and therefore biasing model design.
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- Will Trespassers Be Prosecuted or Assessed According to Their Merits? A Consilient Interpretation of Territoriality in a Group-Living Carnivore, the European Badger (Meles meles)
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Socio-spatial interactions of Carnivores have traditionally been described using the vocabulary of territoriality and aggression, with scent marks interpreted as ‘scent fences’. Here, we investigate the role of olfactory signals in assumed territorial marking of group-living solitary foragers using European badgers Meles meles as a model. We presented anal gland secretions (n = 351) from known individuals to identifiable recipients (n = 187), to assess response-variation according to familiarity (own-group, neighbours, strangers) and spatial context (in-context: at a shared border; out-of-context: at an unshared border/ the main sett). Sniffing and over-marking (with subcaudal gland secretion) responses were strongest to anal gland secretions from strangers, intermediate to neighbouring-group and weakest to own-group members. Secretions from both, strangers and neighbours, were sniffed for longer than were own-group samples, although neighbour-secretion presented out-of-context evoked no greater interest than in-context. On an individual level, responses were further moderated by the relevance of individual-specific donor information encoded in the secretion, as it related to the physiological state of the responder. There was a trend bordering on significance for males to sniff for longer than did females, but without sex-related differences in the frequency of subcaudal over-marking responses, and males over-marked oestrous female secretions more than non-oestrous females. There were no age-class related differences in sniff-duration or in over-marking. Evaluating these results in the context of the Familiarity hypothesis, the Threat-level hypothesis, and the Individual advertisement hypothesis evidences that interpretations of territorial scent-marks depicting rigid and potentially agonistic discrimination between own- and foreign-group conspecifics are overly simplistic. We use our findings to advance conceptual understanding of badger socio-spatial ecology, and the general context of territoriality and group-range dynamics.
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- Climate and the Individual: Inter-Annual Variation in the Autumnal Activity of the European Badger (Meles meles)
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We establish intra-individual and inter-annual variability in European badger (Meles meles) autumnal nightly activity in relation to fine-scale climatic variables, using tri-axial accelerometry. This contributes further to understanding of causality in the established interaction between weather conditions and population dynamics in this species. Modelling found that measures of daylight, rain/humidity, and soil temperature were the most supported predictors of ACTIVITY, in both years studied. In 2010, the drier year, the most supported model included the SOLAR*RH interaction, RAIN, and30cmTEMP (w = 0.557), while in 2012, a wetter year, the most supported model included the SOLAR*RH interaction, and the RAIN*10cmTEMP (w = 0.999). ACTIVITY also differed significantly between individuals. In the 2012 autumn study period, badgers with the longest per noctem activity subsequently exhibited higher Body Condition Indices (BCI) when recaptured. In contrast, under drier 2010 conditions, badgers in good BCI engaged in less per noctem activity, while badgers with poor BCI were the most active. When compared on the same calendar dates, to control for night length, duration of mean badger nightly activity was longer (9.5 hrs ±3.3 SE) in 2010 than in 2012 (8.3 hrs ±1.9 SE). In the wetter year, increasing nightly activity was associated with net-positive energetic gains (from BCI), likely due to better foraging conditions. In a drier year, with greater potential for net-negative energy returns, individual nutritional state proved crucial in modifying activity regimes; thus we emphasise how a ‘one size fits all’ approach should not be applied to ecological responses.
- Related item:
- A new Magneto-Inductive tracking technique to uncover subterranean activity: what do animals do underground?
- Description:
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Despite the importance of the subterranean ecotope, knowledge of underground movement and behaviour has been extremely limited. Previous technologies have relied upon techniques with very low spatial or temporal resolution, such as VHF telemetry. Rather incongruously, therefore, relatively simple underground activity regimes have often been assumed, with insufficient attention to the ecological importance of burrow use.
We test the capability of Magneto-Inductive (MI) tracking, recording underground movement within a European badger sett over a 2 week period in February. These data allowed us to: quantify subterranean movement; extrapolate the three-dimensional burrow architecture; simultaneously track multiple individuals; and establish the function of specific movement patterns; demonstrating the technique's utility. Contrasting data generated using MI tracking, against the resolution achievable with VHF tracking, we establish how sampling frequency can influence the perception of movement.
Taking 20 locational fixes per minute, MI collars operated for 1 year before on-board batteries failed, resulting in an average five billion data points per collar deployment. Socio-ecologically we found that rather than foraging continuously throughout the night, badgers returned to the sett an average of 2·2 times, approximately every 3–4 h. From burrow mapping, badgers tended to use peripheral chambers for c. 45 min on these return visits. These outlying chambers were used less by day, when badgers selected deeper chambers, suggesting each chamber type fulfils a different function. This technology also exposed that badgers exhibited a far greater extent of underground movement than revealed by former technologies, which by comparison captured <0·5% of subterranean activity. Importantly, these high-resolution data showed that individuals left, returned to, and moved about the sett independently, with no tendency for synchronous subterranean activity.
In overview, Magneto-Inductive tracking proved relatively simple and cost-effective to deploy, it provided very detailed and accurate subterranean fixes, and was robust enough for long-term field deployment. Furthermore, the capabilities of MI are highly transferable, enabling a better understanding of underground activity and the ecological importance of subterranean burrows for the conservation and management of a wide range of species.
