On the Relationship between Herbaceous Cover and Vigilance Activity of Degus (Octodon degus)

Antelope space‐use and behavior indicate multilevel responses to varying anthropogenic influences in a highly human‐dominated landscape

A primary means of conserving a species or a habitat in a human‐dominated landscape is through promoting coexistence with humans while minimizing conflict. For this, we should understand how wildlife is impacted by direct and indirect human activities. Such information is rare in areas with high human densities. To investigate how animals respond to altered ecological conditions in human‐dominated landscapes, we focused on a wild herbivore of conservation concern in the Krishnasaar Conservation Area (KrCA) in Nepal. Here, blackbuck Antilope cervicapra, a generalist grazer, lives in refugia located with a growing human population. We studied the impacts of humans on habitat use and behavior of blackbuck. We laid 250 × 250 m grid cells in the entire KrCA and carried out indirect sign surveys with three replications for habitat use assessment. We observed herds of blackbuck for 89 h in different habitat types using scan sampling methods. Our habitat‐use survey showed that habitats under intensive human use were hardly used by blackbuck, even when high‐quality forage was available. Habitat openness was the major predictor of habitat use inside the core area, where levels of human activities were low. We also found a positive correlation between habitat use by blackbuck and livestock. Blackbuck were substantially more vigilant when they were in forest than in grassland, again indicating an influence of risk. Overall, blackbuck appear to be sensitive to the risk associated with both natural and anthropogenic factors. Our findings have direct implications for managing human–wildlife interactions in this landscape, specifically regarding strategies for livestock grazing in habitats highly used by blackbuck and concerning predictions of how changing land use will impact the long‐term persistence of blackbuck. Our work suggests that wild herbivores may be able to persist in landscapes with high human densities so long as there are refuges where human activities are relatively low.

Burrowing and Anti-Predator Requirements Determine the Microhabitat Selection of Himalayan Marmot in Zoige Wetland

To satisfy their requirements for food and safety, animals need certain habitats to live. Marmots generally select habitats with certain elevation, land surface temperature, soil and vegetation type, and certain mountain slope and aspect; however, what habitats are needed at relatively smaller scales are poorly known. The Himalayan marmot (Marmota himalayana) is distributed mainly on the Qinghai-Tibet Plateau, a region exhibiting diversified topographic features, and the Zoige wetland in the northeast part of the plateau is also the home of the Himalayan marmot. The region is famous for its plateau peat bog, and the suitable habitats for Himalayan marmots are patchily distributed in the wetland. To investigate what kinds of patches are preferred by the marmot in this wetland ecosystem, we measured and compared the soil and vegetation characteristics of used and unused patches. We found that unlike factors governing the habitat selection at macroscales, patches characterized by flat ground and low soil moisture content, with medium vegetation standing height and low vegetation density, are selected in the Zoige wetland. Patches of this kind are selected to meet the marmots' requirements for burrow construction and predator avoidance in such a wetland ecosystem. Together with previous studies on habitat selection of the marmot species at macroscales, we showed that to explore how the animals survive in an environment, it is important to conduct the analysis at multiple scales.

Habitat-dependent changes in vigilance behaviour of Red-crowned Crane influenced by wildlife tourism

The Endangered Red-crowned Crane (Grus japonensis) is one of the most culturally iconic and sought-after species by wildlife tourists. Here we investigate how the presence of tourists influence the vigilance behaviour of cranes foraging in Suaeda salsa salt marshes and S. salsa/Phragmites australis mosaic habitat in the Yellow River Delta, China. We found that both the frequency and duration of crane vigilance significantly increased in the presence of wildlife tourists. Increased frequency in crane vigilance only occurred in the much taller S. salsa/P. australis mosaic vegetation whereas the duration of vigilance showed no significant difference between the two habitats. Crane vigilance declined with increasing distance from wildlife tourists in the two habitats, with a minimum distance of disturbance triggering a high degree of vigilance by cranes identified at 300 m. The presence of wildlife tourists may represent a form of disturbance to foraging cranes but is habitat dependent. Taller P. australis vegetation serves primarily as a visual obstruction for cranes, causing them to increase the frequency of vigilance behaviour. Our findings have important implications for the conservation of the migratory red-crowned crane population that winters in the Yellow River Delta and can help inform visitor management.

Assessing anti-predator decisions of foraging eastern chipmunks under varying perceived risks: the effects of physical and social environments on vigilance

Animals foraging under risk have to trade-off resource acquisition and predator avoidance. Environmental factors can modulate the level of risk and should thus influence the expression of anti-predator behaviours such as vigilance. In this study, we investigated the effects of physical and social environments on eastern chipmunks’ (Tamias striatus) vigilance, by varying the perceived risk through playback experiments of alarm calls and neutral environmental sounds, and by integrating habitat and weather characteristics, as well as neighbour density. Chipmunks showed higher levels of vigilance when foraging in more open habitats, under high wind conditions, when they heard alarm calls and when surrounded by a high neighbour density. The effects of wind intensity and neighbour density on vigilance were also stronger during the broadcast of alarm calls rather than neutral sounds. Our results emphasize how both the physical and social environments can modify risk perception and therefore risk-taking decisions of foraging individuals.

Antipredator behaviour of domestic guinea pigs (Cavia porcellus)

The objective of this study was to test the reactions of domestic guinea pigs to the presence of aerial and terrestrial predators in a laboratory setting. We measured the behavioural reactions of 27 adolescent guinea pigs to the presence of a dog, imitation of a bird of prey and an unknown human as control. Kruskal-Wallis ANOVA and Mann-Whitney U Test were used to analyse the differences in duration and frequency of responses (freezing, fleeing, and vigilance) to predators. When confronted with the dog, guinea pigs reacted for the longest time and most frequently by freezing. In presence of the bird of prey, they responded for the longest time and most often by freezing and fleeing. In presence of a human, they showed mostly vigilance. When comparing reactions to the dog and human, there were differences in duration and frequency of freezing and fleeing. When comparing reactions to the bird of prey and control test, we observed differences between fleeing and vigilance. The durations and frequencies of freezing, fleeing and vigilance to the dog and bird of prey were different. The only differences in reactions of males and females occurred in duration and frequency of fleeing in presence of the bird of prey. No vocalization was observed except for two occurrences, of a “drrr” and a “chirrup”. Our results indicate that domestic guinea pigs tested under laboratory conditions can discriminate between a terrestrial and an aerial predator, when exposed to them individually. Their antipredator behaviours remained functional, although their vocalizations may have been affected by the absence of signal receivers.

Similarities in perceived predation risk prevent temporal partitioning of food by rodents in an African grassland

One way in which animals coexist is through temporal separation of feeding activities. This separation directly reduces interference competition, but potentially not exploitive competition. To reduce exploitive competition, coexisting species tend to utilize different microhabitats and/or achieve different feeding efforts across microhabitats. However, 1 factor that has generally not been considered with regards to its impacts on competition, and thus coexistence, is predation risk. As different predators are active during the day and at night, the location of safe areas across the landscape can vary temporally. If so, then temporally separated prey species would likely forage in different areas thus reducing exploitive competition. However, if predation risk across the landscape is similar for nocturnal and diurnal species, then both could restrict their foraging to the same microhabitats, thus increasing exploitive competition. To explore these alternative possibilities, we manipulated grass height in an African grassland to create microhabitats that varied in predation risk. We then estimated perceived predation risk of both nocturnal and diurnal rodents in these microhabitats by recording giving-up densities (GUDs) in artificial resource patches. We found that despite differences in predators, both nocturnal and diurnal rodents preferred feeding in the same microhabitats, and they achieved similar feeding efforts within these microhabitats. This suggests that despite the prevention of interference competition through temporal partitioning, the spatial similarities in perceived predation risk in relation to cover likely increase exploitive competition between these rodents. However, as both nocturnal and diurnal rodents were present in the study area, it is likely that some other mechanism (e.g., varied diets) allows them to coexist.

Seasonal variation in the degu (Octodon degus) endocrine stress response

Many wild animals show seasonal variation in circulating levels of stress hormones. Seasonal changes in the stress response may help animals better cope with the different challenges faced during each life history stage. We determined the seasonal stress profile of wild, free-living degus in Chile. Female degus were sampled during non-breeding (January), mating/early gestation (July), late gestation (August), and lactation (1st litter-September, 2nd litter-January). Male degus were sampled during the first three time-points. We measured baseline cortisol (CORT), stress-induced CORT, and negative feedback efficacy using a dexamethasone suppression test. While we found that neither males nor females showed seasonal variation in baseline CORT or negative feedback levels, we did find significant seasonal variation in stress-induced CORT levels of both sexes. Male stress-induced CORT was lowest during mating while female stress-induced CORT was highest during late gestation and lactation. Overall, females had higher stress-induced CORT compared to males. Our data suggest that stress-induced levels of CORT are highest during periods with increased chance of stressor exposure or times of positive energy balance. Consequently, CORT responses to stress appear to be regulated according to different life history needs.

Habitat type influences endocrine stress response in the degu (Octodon degus)

While many studies have examined whether the stress response differs between habitats, few studies have examined this within a single population. This study tested whether habitat differences, both within-populations and between-populations, relate to differences in the endocrine stress response in wild, free-living degus (Octodon degus). Baseline cortisol (CORT), stress-induced CORT, and negative feedback efficacy were measured in male and female degus from two sites and three habitats within one site during the mating/early gestation period. Higher quality cover and lower ectoparasite loads were associated with lower baseline CORT concentrations. In contrast, higher stress-induced CORT but stronger negative feedback efficacy were associated with areas containing higher quality forage. Stress-induced CORT and body mass were positively correlated in female but not male degus across all habitats. Female degus had significantly higher stress-induced CORT levels compared to males. Baseline CORT was not correlated with temperature at time of capture and only weakly correlated with rainfall. Results suggest that degus in habitats with good cover quality, low ectoparasite loads, and increased food availability have decreased endocrine stress responses.

Ecological drivers of group living in two populations of the communally rearing rodent, Octodon degus

Intraspecific variation in sociality is thought to reflect a trade-off between current fitness benefits and costs that emerge from individuals' decision to join or leave groups. Since those benefits and costs may be influenced by ecological conditions, ecological variation remains a major, ultimate cause of intraspecific variation in sociality. Intraspecific comparisons of mammalian sociality across populations facing different environmental conditions have not provided a consistent relationship between ecological variation and group-living. Thus, we studied two populations of the communally rearing rodent Octodon degus to determine how co-variation between sociality and ecology supports alternative ecological causes of group living. In particular, we examined how variables linked to predation risk, thermal conditions, burrowing costs, and food availability predicted temporal and population variation in sociality. Our study revealed population and temporal variation in total group size and group composition that covaried with population and yearly differences in ecology. In particular, predation risk and burrowing costs are supported as drivers of this social variation in degus. Thermal differences, food quantity and quality were not significant predictors of social group size. In contrast to between populations, social variation within populations was largely uncoupled from ecological differences.

Heritability of anti-predatory traits: vigilance and locomotor performance in marmots

Animals must allocate some proportion of their time to detecting predators. In birds and mammals, such anti-predator vigilance has been well studied, and we know that it may be influenced by a variety of intrinsic and extrinsic factors. Despite hundreds of studies focusing on vigilance and suggestions that there are individual differences in vigilance, there have been no prior studies examining its heritability in the field. Here, we present one of the first reports of (additive) genetic variation in vigilance. Using a restricted maximum likelihood procedure, we found that, in yellow-bellied marmots (Marmota flaviventris), the heritability of locomotor ability (h(2)=0.21), and especially vigilance (h(2) = 0.08), is low. These modest heritability estimates suggest great environmental variation or a history of directional selection eliminating genetic variation in these traits. We also found a significant phenotypic (r(P) = -0.09 +/- 0.04, P = 0.024) and a substantial, but not significant, genetic correlation (r(A) = -0.57 +/- 0.28, P = 0.082) between the two traits (slower animals are less vigilant while foraging). We found no evidence of differential survival or longevity associated with particular phenotypes of either trait. The genetic correlation may persist because of environmental heterogeneity and genotype-by-environment interactions maintaining the correlation, or because there are two ways to solve the problem of foraging in exposed areas: be very vigilant and rely on early detection coupled with speed to escape, or reduce vigilance to minimize time spent in an exposed location. Both strategies seem to be equally successful, and this 'locomotor ability-wariness' syndrome may therefore allow slow animals to compensate behaviourally for their impaired locomotor ability.

Flight initiation distance is differentially sensitive to the costs of staying and leaving food patches in a small-mammal prey

Escape theory predicts that a prey should flee from an approaching predator at a point in which the cost of staying equals the cost of escape. We manipulated the cost of fleeing upon approaching human predators by providing the small mammal Octodon degus (Molina, 1782) with varying amounts of supplementary food likely to disappear while the animals are not in the food patch (e.g., hidden in their burrows). Simultaneously, we manipulated the risk of remaining in the patch by providing supplementary food at varying distances from the nearest burrow. Degus fled at a shorter distance to approaching predators when foraging in patches closer to the nearest burrow and supplied with relatively high abundance of food, but only when these rodents were foraging socially. Also, degus fled at a greater distance to approaching predators when foraging in patches far from the nearest burrow. Thus, functions linked to the loss of feeding opportunities and the risk of predation interact to influence flight initiation distance after a simulated attack. This study represented one of the few demonstrations of an interactive effect between cost and risks on antipredator behavior in a small, social prey mammal.

The importance of indirect cues for white-browed sparrow-weaver (Plocepasser mahali) risk assessment

Both direct cues that provide information about the actual presence of a predator and indirect environmental cues that provide information about the probability of encountering a predator may be used by animals assessing predation risk, but relatively few studies manipulate both simultaneously to study their relative importance. We conducted two experiments to study the foraging decisions of white-browed sparrow-weavers (Plocepasser mahali). The first experiment manipulated both direct and indirect cues in a feeding array by simultaneously placing feeding stations at different distances from humans (to manipulate direct risk) and from protective cover (to manipulate indirect risk). Weaver foraging was influenced more by indirect risk than by direct risk. The second experiment aimed to determine if weaver’s indirect risk assessment was sensitive to variation in benefits. We set two feeding stations at different distances from cover but the same distance from the human observers and systematically increased the amount of food at the station farther from cover. Weavers far from cover initially foraged at higher rates than those close to cover, but the addition of food reduced the foraging rate. Together, our results illustrate that weaver foraging decisions are sensitive to variation in risk and that indirect cues are relatively more important than direct cues.

Ecological and hormonal correlates of antipredator behavior in adult Belding's ground squirrels (Spermophilus beldingi)

Predator-prey relationships provide an excellent opportunity to study coevolved adaptations. Decades of theoretical and empirical research have illuminated the various behavioral adaptations exhibited by prey animals to avoid detection and capture, and recent work has begun to characterize physiological adaptations, such as immune reactions, metabolic changes, and hormonal responses to predators or their cues. A 2-year study quantified the activity budgets and antipredator responses of adult Belding's ground squirrels (Spermophilus beldingi) living in three different California habitats and likely experiencing different predation pressures. At one of these sites, which is visually closed and predators and escape burrows are difficult to see, animals responding to alarm calls remain alert longer and show more exaggerated responses than adults living in two populations that likely experience less intense predation pressure. They also spend more time alert and less time foraging than adults at the other two sites. A 4-year study using noninvasive fecal sampling of cortisol metabolites revealed that S. beldingi living in the closed site also have lower corticoid levels than adults at the other two sites. The lower corticoids likely reflect that predation risk at this closed site is predictable, and might allow animals to mount large acute cortisol responses, facilitating escape from predators and enhanced vigilance while also promoting glucose storage for the approaching hibernation. Collectively, these data demonstrate that local environments and perceived predation risk influence not only foraging, vigilance, and antipredator behaviors, but adrenal functioning as well, which may be especially important for obligate hibernators that face competing demands on glucose storage and mobilization.