Foraging behaviour at multiple temporal scales in a wild alpine equid

Collective decision-making and spatial patterns in orientation of an endemic ungulate on the Tibetan Plateau

Group living animals form striking aggregation patterns and display synchronization, polarization, and collective intelligence. Though many collective behavioral studies have been conducted on small animals like insects and fish, research on large animals is still rare due to the limited availability of field collective data. We used drones to record videos and analyzed the decision-making and behavioral spatial patterns in orientation of Kiang (Tibetan wild ass, Equus kiang). Leadership is unevenly distributed among Kiang, with the minority initiating majority behavior-shift decisions. Decisions of individual to join are driven by imitation between group members, and are largely dependent on the number of members who have already joined. Kiang respond to the behavior and position of neighbors through different strategies. They strongly polarize when moving, therefore adopting a linear alignment. When vigilant, orientation deviation increases as they form a tighter group. They remain scattered while feeding and, in that context, adopt a side-by-side alignment. This study reveals partially-shared decision-making among Kiang, whereby copying neighbors provides the wisdom to thrive in harsh conditions. This study also suggests that animals' spatial patterns in orientation depend largely on their behavioral states in achieving synchronization.

Locomotor activity patterns of takin (Budorcas taxicolor) in a temperate mountain region

Understanding locomotor activity patterns would reveal key information about an animal’s foraging strategy, energy budget and evolutionary adaptation. We studied the locomotor activity patterns of the takin (Budorcas taxicolor) in a temperate mountain region in China using GPS radio-collar technology from 1 July 2014 to 30 June 2015. Our research showed that takin had a bimodal crepuscular locomotor activity pattern, with an especially obvious movement peak at dusk. The takins showed significant seasonal differences in their movement rates, with the lowest movement rate in winter. The animals also showed sexual differences in their movement rates. In spring, the female movement rate was significantly higher than that of males during daytime, while during nighttime the movement rate of males was higher than that of females. The male movement rate was significantly higher than that of females in summer. The movement rate of the takins were correlated to microenvironment temperature and normalized difference vegetation index (NDVI) in each season. These findings suggest that takin could adjust locomotor activity levels adapt to reproductive requirements, temperature variation and forage variability.

Joint effects of weather and interspecific competition on foraging behavior and survival of a mountain herbivore

Weather variations have the potential to influence species interactions, although effects on competitive interactions between species are poorly known. Both weather and competition can influence foraging behavior and survival of herbivores during nursing/weaning, a critical period in the herbivore life cycle. We evaluated the joint effects of weather and competition with red deer Cervus elaphus on the foraging behavior of adult female Apennine chamois Rupicapra pyrenaica ornata in summer, and on winter survival of chamois kids. High temperature and low rainfall during the growing season of vegetation had negative effects on bite rate. Effects of weather were greater in forb patches, including cold-adapted, nutritious plants of key importance to chamois, than in graminoid ones. Our results confirm previous indications of a negative effect of competition on bite rate of female chamois and on kid survival. Furthermore, harsh weather conditions and competition with deer had additive, negative roles on foraging behavior and survival of chamois. Growing temperatures are expected to influence distribution, growth, and/or nutritional quality of plants; competition would reduce pasture quality and food availability through resource depletion. Both factors would limit food/energy intake rates during summer, reducing survival of the youngest cohorts in winter. We suggest that interspecific competition can be an important additive factor to the effects of weather changes on behavior and demography.

The discovery of the ‘transient’ male Tibetan wild ass: alternative ‘sneaky’ mating tactics in a wild equid?

Male asses usually consist of two classes, social bachelors and solitary, territorial males. However, our observations of the Tibetan wild ass (Equus kiang) suggested a third class may exist. Unexpectedly, unidentified males were often found courting females within another male’s territory. To test our hypothesis that a new social class existed, we compared 12 social behaviours among three putative groups. The third male-type spent less time herding and demonstrating flehmen, while spending more time retreating, trotting and in proximity of females, where they were more likely to engage in courtship and urine-marking. Based on increased time spent among females within other territories, the most courtship events, and minimal time invested in each courtship, they appear to employ ‘sneaky’ mating tactics. We discuss whether these ‘transient’ males are demonstrating an adaptive alternative mating strategy, or whether these behaviours result from a discrete developmental stage of bachelors unready to challenge a rival.

Activity budgets and behavioural synchrony in a wild equid living in a fission-fusion social system

Variation in activity budgets among individuals of different age-sex classes and reproductive status may lead to decreases in behavioural synchrony (i.e., individuals performing the same behaviour at the same time in the same group) in social species. Here, we assessed the costs of behavioural synchrony in terms of time allocated to feeding behaviour among individuals of different age-sex classes and reproductive status in the kiang (Equus kiang), a poorly known wild equid that inhabits the Tibetan Plateau. Our study was conducted in Eastern Ladakh (India), during summer and fall. Our results showed that groups were highly synchronized, and that individuals in groups were particularly synchronized when feeding. Despite a slight sexual dimorphism, males and females had similar activity budgets. Males in groups, however, spent less time feeding than solitary males, and females in groups with foals spent less time feeding and more time standing than females in groups without foals. We suggest that group formation in males and the presence of foals for females incur behavioural costs by lowering their time spent feeding. Because these costs occur at a predictable time of the year, it could be profitable for adult kiangs not to form permanent groups year-round. Individuals with divergent needs might benefit from the loose social system observed in kiangs, which could be a key feature of their adaptation to a highly seasonal environment.

Field measurements give biased estimates of functional response parameters, but help explain foraging distributions

Mechanistic insights and predictive understanding of the spatial distributions of foragers are typically derived by fitting either field measurements on intake rates and food abundance, or observations from controlled experiments, to functional response models. It has remained unclear, however, whether and why one approach should be favoured above the other, as direct comparative studies are rare. The field measurements required to parameterize either single or multi-species functional response models are relatively easy to obtain, except at sites with low food densities and at places with high food densities, as the former will be avoided and the second will be rare. Also, in foragers facing a digestive bottleneck, intake rates (calculated over total time) will be constant over a wide range of food densities. In addition, interference effects may depress intake rates further. All of this hinders the appropriate estimation of parameters such as the 'instantaneous area of discovery' and the handling time, using a type II functional response model also known as 'Holling's disc equation'. Here we compare field- and controlled experimental measurements of intake rate as a function of food abundance in female bar-tailed godwits Limosa lapponica feeding on lugworms Arenicola marina. We show that a fit of the type II functional response model to field measurements predicts lower intake rates (about 2.5 times), longer handling times (about 4 times) and lower 'instantaneous areas of discovery' (about 30-70 times), compared with measurements from controlled experimental conditions. In agreement with the assumptions of Holling's disc equation, under controlled experimental settings both the instantaneous area of discovery and the handling time remained constant with an increase in food density. The field data, however, would lead us to conclude that although handling time remains constant, the instantaneous area of discovery decreased with increasing prey densities. This will result into highly underestimated sensory capacities when using field data. Our results demonstrate that the elucidation of the fundamental mechanisms behind prey detection and prey processing capacities of a species necessitates measurements of functional response functions under the whole range of prey densities on solitary feeding individuals, which is only possible under controlled conditions. Field measurements yield 'consistency tests' of the distributional patterns in a specific ecological context.

Resource selection in a high-altitude rangeland equid, the kiang (Equus kiang): influence of forage abundance and quality at multiple spatial scales

Herbivores foraging in arid and seasonal environments often face choices between plant patches varying in abundance and nutritional quality at several spatial and temporal scales. Because of their noncompartmented digestive system, equids typically rely on abundant forage to meet their nutrient requirements. In forage-limited environments, therefore, scarcity of food resources represents a challenge for wild equids. We investigated hierarchical resource-selection patterns of kiangs (Equus kiang Moorcroft, 1841), a wild equid inhabiting the high-altitude steppes of the Tibetan Plateau, hypothesizing that vegetation abundance would be the main factor driving resource selection at a large scale and that plant quality would influence resource selection at finer scales. We investigated resource-selection patterns at three spatial levels (habitat, feeding site, and plant (vegetation groups, i.e., grasses, sedges, forbs, and shrubs)) during summer and fall. At the habitat level, kiangs selected both mesic and xeric habitats in summer and only xeric habitats (plains) during fall. At the feeding-site level, feeding sites had higher plant biomass and percentage of green foliage than random sites in the same habitats. At the plant level, grasses were selected over forbs and shrubs, and sedges were used in proportion to their availability during all seasons. Our results indicate that resource-selection patterns in kiangs vary across scales and that both forage abundance and quality play a role in resource selection. Plant quality appeared more important than hypothesized, possibly to increase daily nutrient intake in forage-limited and highly seasonal high-altitude rangelands.

Spatiotemporal variations in resources affect activity and movement patterns of white-tailed deer (Odocoileus virginianus) at high density

Although activity budget, movements, and habitat use of herbivores have been extensively studied, few studies have simultaneously examined these behaviors at several temporal scales. We investigated the influence of spatiotemporal variations in forage and climate on the activity and movement patterns of white-tailed deer (Odocoileus virginianus (Zimmermann, 1780)) at high density, in a predator-free ecosystem impacted by long-term browsing. We used GPS telemetry and activity sensors to monitor seasonal activity budgets, movements, and patterns of habitat use within the home ranges of 24 female deer at three temporal scales: (1) season, (2) within season, and (3) daily. At large temporal scale, deer were less active and moved less during winter than during summer. Within each season, deer reduced their activity and movements in areas where forage resources were abundant and when climatic conditions were more difficult. On a daily scale, summer and winter movements peaked at dusk, but habitat selection neither changed with period of the day nor activity (foraging vs. resting). These results provide empirical evidence on how environmental constraints can modulate the trade-offs between forage acquisition and exposure to limiting factors.