The landscape of fear: Why some free-ranging rodents choose repeated live-trapping over predation risk and how it is associated with the physiological stress response

The Landscape of Fear as a Safety Eco-Field: Experimental Evidence

In a development of the ecosemiotic vivo-scape concept, a 'safety eco-field' is proposed as a model of a species response to the safety of its environment. The safety eco-field is based on the ecosemiotic approach which considers environmental safety as a resource sought and chosen by individuals to counter predatory pressure. To test the relative safety of different locations within a landscape, 66 bird feeders (BF) were deployed in a regular 15 × 15 m grid in a rural area, surrounded by shrubs, small trees, hedgerows, and buildings. On each of 48 days in November 2021 and February and March 2022, dried mealworms were placed on each BF and counts of larvae at each BF were made at noon and dusk. The European robin (Erithacus rubecula) and the great tit (Parus major) were the most regular visitors to the BFs. Land cover at each BF was recorded. Bird behaviour at the BFs was noted from direct video recordings of the birds at nine selected BFs, totalling 32 daily sessions in March. The different behaviours of the European robin and the great tit were observable. The safety eco-field changed according to the month and the time of day. The distance of the BF from the woodland edges seemed to be important only in the morning. In the afternoon, BFs that were more distant from the woodland edges received the highest number of visits. Weather conditions were found to influence the number of mealworms removed, but this requires further investigation. A significant relationship between land cover and the number of mealworm larvae removed from the BFs was observed. Within the grid of BF, three regions were distinguishable which were related to land cover in the safety eco-field process. The experimental framework confirms the adequacy, at least for birds that have cryptic predators, to map the landscape as a proxy of safety resource. From the video recordings it was noted that the European robin visits were distributed throughout the day without apparent temporal preferences, while the great tit visits were concentrated in the central part of the day. This result has the limitation of the short period of observation (March) and should be extended to the entire period of the experiment to eventually capture seasonal variation. The experimental evidence obtained confirms that the ecosemiotic-based models of safety eco-field are an efficient approach to explain bird feeding preferences and behaviours.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12304-023-09522-1.

Profiles of animal consciousness: A species-sensitive, two-tier account to quality and distribution

The science of animal consciousness investigates (i) which animal species are conscious (the distribution question) and (ii) how conscious experience differs in detail between species (the quality question). We propose a framework which clearly distinguishes both questions and tackles both of them. This two-tier account distinguishes consciousness along ten dimensions and suggests cognitive capacities which serve as distinct operationalizations for each dimension. The two-tier account achieves three valuable aims: First, it separates strong and weak indicators of the presence of consciousness. Second, these indicators include not only different specific contents but also differences in the way particular contents are processed (by processes of learning, reasoning or abstraction). Third, evidence of consciousness from each dimension can be combined to derive the distinctive multi-dimensional consciousness profile of various species. Thus, the two-tier account shows how the kind of conscious experience of different species can be systematically compared.

Long-Tailed Pygmy Rice Rats Modify Their Behavioural Response and Faecal Corticosterone Metabolites in Response to Culpeo Fox but Not to Lesser Grison

Simple Summary

Prey species must fine-tune their antipredator responses to survive, but also to achieve a positive net energy balance which will enhance biological fitness. Given this, we investigated if Oligoryzomys longicaudatus would adapt their behavioural and physiological antipredator responses depending on their relative presence in the predator’s diet. By exposing this rodent species to culpeo fox and lesser grison faeces, we found that O. longicaudatus behavioural and physiological strategies were modulated depending on the predator’s diet. Specifically, rodents would trigger their antipredator responses in the presence of the most dangerous predator, the culpeo, which consumes a higher proportion of O. longicaudatus compared to the lesser grison. Our findings could be of importance for the development of more humane and efficient strategies to control rodent populations.

Abstract

Even though behavioural and physiological reactions to predation risk exhibited by prey species have received considerable attention in scientific journals, there are still many questions still unsolved. Our aim was to broaden the knowledge on one specific question: do long-tailed pygmy rice rats adapt their behavioural and physiological antipredator strategies depending on the predator species? For this question, we live-trapped in a temperate forest in Southern Chile long-tailed pygmy rice rats (Oligoryzomys longicaudatus), which were exposed to three predator odour phases (Phase 0: preliminary, no predator cues; Phase 1: one plot with culpeo fox faeces (Lycalopex culpaeus), one plot with lesser grison (Galictis cuja) faeces and one plot acting as a control with no odour; Phase 2: post treatment, no predator cues). We measured the behavioural response by the capture ratio. To assess the physiological stress response, we collected fresh faecal samples to quantify faecal corticosterone metabolites (FCM). Our results showed that O. longicaudatus increased both the capture ratio and FCM levels in the presence of culpeo cues. Culpeo foxes have higher densities in the study area than G. cuja and exhibit a higher activity pattern overlap with O. longicaudatus. Moreover, it has been also been reported in other regions that L. culpaeus consumption of O. longicaudatus is more frequent compared to G. cuja diet. The increase in capturability could be because traps can be regarded as a shelter in high-risk settings, but it can also be explained by the predator inspection behaviour. The increase in FCM concentrations during culpeo treatment can be linked to the adaptive mobilisation of energy to execute antipredator responses to increase survival chances.

Heterothermy as a mechanism to offset energetic costs of environmental and homeostatic perturbations

Environmental and biotic pressures impose homeostatic costs on all organisms. The energetic costs of maintaining high body temperatures (Tb) render endotherms sensitive to pressures that increase foraging costs. In response, some mammals become more heterothermic to conserve energy. We measured Tb in banner-tailed kangaroo rats (Dipodomys spectabilis) to test and disentangle the effects of air temperature and moonlight (a proxy for predation risk) on thermoregulatory homeostasis. We further perturbed homeostasis in some animals with chronic corticosterone (CORT) via silastic implants. Heterothermy increased across summer, consistent with the predicted effect of lunar illumination (and predation), and in the direction opposite to the predicted effect of environmental temperatures. The effect of lunar illumination was also evident within nights as animals maintained low Tb when the moon was above the horizon. The pattern was accentuated in CORT-treated animals, suggesting they adopted an even further heightened risk-avoidance strategy that might impose reduced foraging and energy intake. Still, CORT-treatment did not affect body condition over the entire study, indicating kangaroo rats offset decreases in energy intake through energy savings associated with heterothermy. Environmental conditions receive the most attention in studies of thermoregulatory homeostasis, but we demonstrated here that biotic factors can be more important and should be considered in future studies.

Behavioral Responses of Wild Rodents to Owl Calls in an Austral Temperate Forest

Simple Summary

Growing human populations are challenging scientists to find effective ways to control and mitigate human–wildlife conflict while preserving biodiversity. It has been reported that predator odor and calls can drive away rodents, but little is known about species-specific responses of prey. For these reasons, we compared the behavioral changes of common rodent species inhabiting the Chilean temperate forest (Abrothrix spp., the long-tailed pygmy rice rat Oligoryzomyslongicaudatus and the black rat Rattus rattus) when exposed to two different native predator calls (the austral pygmy owl Glaucidium nana and the rufous-legged owl Strix rufipes) and a control (no predator calls). Our results showed that all rodent species modified their behavior in the presence of predator calls, but the effects were species dependent. These findings point to the need to carefully study target rodent species instead of applying a general control plan for all rodent species.

Abstract

Ecologically based rodent management strategies are arising as a sustainable approach to rodent control, allowing us to preserve biodiversity while safeguarding human economic activities. Despite predator signals being known to generally repel rodents, few field-based studies have compared the behavioral effects of several predators on different prey species, especially in Neotropical ecosystems. Here, we used camera traps to study the behavior of rodent species native to the Chilean temperate forest (Abrothrix spp., long-tailed pygmy rice rat Oligoryzomys longicaudatus) and an introduced rodent (black rat Rattus rattus). Using playbacks of raptor calls, we experimentally exposed rodents to three predation risk treatments: austral pygmy owl calls (Glaucidium nana), rufous-legged owl calls (Strix rufipes) and a control treatment (absence of owl calls). We evaluated the effects of the treatments on the time allocated to three behaviors: feeding time, locomotor activity and vigilance. Moonlight and vegetation cover were also considered in the analyses, as they can modify perceived predation risk. Results showed that predator calls and environmental factors modified prey behavior depending not only on the predator species, but also on the rodent species. Consequently, owl playbacks could be regarded as a promising rodent control tool, knowing that future studies would be critical to deeply understand differences between species in order to select the most effective predator cues.

Physical Activity Reduces Epilepsy Incidence: a Retrospective Cohort Study in Swedish Cross-Country Skiers and an Experimental Study in Seizure-Prone Synapsin II Knockout Mice

BACKGROUND

Epilepsy patients commonly exercise less than the general population. Animal studies indicate beneficial effects of physical activity in established epilepsy, while its effect on the development is currently less known.

METHODS

Here, we investigated the incidence of epilepsy during 20 years in a cohort of participants from the long-distance Swedish cross-country ski race Vasaloppet (n = 197,685) and compared it to the incidence of non-participating-matched controls included in the Swedish population register (n = 197,684). Individuals diagnosed with diseases such as stroke and epilepsy before entering the race were excluded from both groups. Experimentally, we also determined how physical activity could affect the development of epilepsy in epilepsy-prone synapsin II knockout mice (SynIIKO), with and without free access to a running wheel.

RESULTS

We identified up to 40-50% lower incidence of epilepsy in the Vasaloppet participants of all ages before retirement. A lower incidence of epilepsy in Vasaloppet participants was seen regardless of gender, education and occupation level compared to controls. The participants included both elite and recreational skiers, and in a previous survey, they have reported a higher exercise rate than the general Swedish population. Sub-analyses revealed a significantly lower incidence of epilepsy in participants with a faster compared to slower finishing time. Dividing participants according to specified epilepsy diagnoses revealed 40-50% decrease in focal and unspecified epilepsy, respectively, but no differences in generalized epilepsy. Voluntary exercise in seizure-prone SynIIKO mice for 1 month before predicted epilepsy development decreased seizure manifestation from > 70 to 40%. Brain tissue analyses following 1 month of exercise showed increased hippocampal neurogenesis (DCX-positive cells), while microglial (Iba1) and astrocytic activation (GFAP), neuronal Map2, brain-derived neurotrophic factor and its receptor tyrosine receptor kinase B intensity were unaltered. Continued exercise for additionally 2 months after predicted seizure onset in SynIIKO mice resulted in a 5-fold reduction in seizure manifestation (from 90 to 20%), while 2 months of exercise initiated at the time of predicted seizure development gave no seizure relief, suggesting exercise-induced anti-epileptogenic rather than anti-convulsive effect.

CONCLUSION

The clinical study and the experimental findings in mice indicate that physical activity may prevent or delay the development of epilepsy.

Wood mouse feeding effort and decision-making when encountering a restricted unknown food source

Animals making foraging decisions must balance the energy gained, the time invested, and the influence of key environmental factors. In our work, we examined the effect of predation risk cues and experience on feeding efforts when a novel food resource was made available. To achieve this, we live-trapped wood mouse Apodemus sylvaticus in Monte de Valdelatas (Madrid), where 80 Sherman traps were set in four plots. Traps were subjected to two food-access difficulties in treatments consisting of three consecutive nights: open plastic bottles (easy) and closed bottles (difficult), both using corn as bait. To simulate predation risk, we set fox faeces in half of the traps in each plot. We also considered moonlight (medium/low) as an indirect predation risk cue. We analysed whether bottles had been bitten by mice and the gnawed area of each bottle was measured. Our results indicated that food access difficulty, experience, and predation risk determined mice feeding decisions and efforts. The ability of mice to adapt feeding effort when a new food source is available was demonstrated because a higher proportion of closed bottles exhibited bite marks and the gnawed area was bigger. Moreover, mouse experience was determinant in the use of this new resource since recaptured mice gnawed broader orifices in the bottles and the gnawed area increased each time an individual was recaptured. Additionally, direct predation risk cues prompted mice to bite the bottles whereas the effect of different moon phases varied among the food access treatments. This study provides direct evidence of formidable efficacy of wild mice to exploit a new nutrient resource while considering crucial environmental factors that shape the decision-making procedure.

The role of steroid hormones and individual traits in food intake in the wood mouse (Apodemus sylvaticus)

Availability of food resources affects animal survival and reproduction. Thus, coping with changes in food availability is one of the most crucial behavioural and physiological processes in wildlife. Food intake is a key concept in animal ecology that is directly conditioned by food quality and abundance or diet choice, but may also vary according to individual-related factors (e.g. foraging behaviours, social rank or energy-demanding periods) and the influence of the endocrine system on energy metabolism. Here, we studied food intake in relation to individual characteristics (sex, breeding condition and age) and whether steroid hormones (testosterone and corticosterone metabolites) mediate food intake in wild wood mouse (Apodemus sylvaticus). Field work was carried out in February-March 2014 in Monte de Valdelatas (Madrid, Spain). Wood mice were live-trapped for 10 consecutive days in four independent plots. Traps were baited with 4 g of toasted corn and food intake was calculated by subtracting the remaining bait found inside traps. Fresh faecal samples from 130 different wood mice were collected and faecal testosterone and corticosterone metabolites (FTM and FCM, respectively) were analysed by enzyme immunoassays. Food intake was higher in females than males, probably due to greater energy requirements. Non-breeders and young individuals also showed a higher food intake. These individuals usually hold a lower social rank which is associated to limited food resources because of dominants; thus, increased food intake may be a result of freely exploit food bait inside traps while avoiding risky competition. In addition, food intake negatively correlated with FTM levels and positively with FCM levels indicating that both hormones have an active role mediating food intake in the wood mouse. Our data suggest that food intake is a function of both individual traits and the endocrine system that accordingly respond throughout different energy-demanding periods.