Measuring Microhabitat Temperature in Arboreal Primates: A Comparison of On-Animal and Stationary Approaches

Behavioral thermoregulation in primates: A review of literature and future avenues

Primates face severe challenges from climate change, with warming expected to increase animals' thermoregulatory demands. Primates have limited long-term options to cope with climate change, but possess a remarkable capacity for behavioral plasticity. This creates an urgency to better understand the behavioral mechanisms primates use to thermoregulate. While considerable information exists on primate behavioral thermoregulation, it is often scattered in the literature in a manner that is difficult to integrate. This review evaluates the status of the available literature on primate behavioral thermoregulation to facilitate future research. We surveyed peer-reviewed publications on primate thermoregulation for N = 17 behaviors across four thermoregulatory categories: activity budgeting, microhabitat use, body positioning, and evaporative cooling. We recorded data on the primate taxa evaluated, support for a thermoregulatory function, thermal variable assessed, and naturalistic/manipulative study conditions. Behavioral thermoregulation was pervasive across primates, with N = 721 cases of thermoregulatory behaviors identified across N = 284 published studies. Most genera were known to utilize multiple behaviors (x ¯  = 4.5 ± 3.1 behaviors/genera). Activity budgeting behaviors were the most commonly encountered category in the literature (54.5% of cases), while evaporative cooling behaviors were the least represented (6.9% of cases). Behavioral thermoregulation studies were underrepresented for certain taxonomic groups, including lemurs, lorises, galagos, and Central/South American primates, and there were large within-taxa disparities in representation of genera. Support for a thermoregulatory function was consistently high across all behaviors, spanning both hot- and cold-avoidance strategies. This review reveals asymmetries in the current literature and avenues for future research. Increased knowledge of the impact thermoregulatory behaviors have on biologically relevant outcomes is needed to better assess primate responses to warming environments and develop early indicators of thermal stress.

Costs of seasonality at a southern latitude: Behavioral endocrinology of female baboons in the Cape Peninsula of South Africa

Environmental challenges in the form of temperature extremes and unusual precipitation, which may lead to prolonged periods outside the thermoneutral zone, can be detrimental to animal physiology. Chacma baboons in the Cape Peninsula of South Africa, one of the highest latitudes at which nonhuman primates are found, experience extremes of both temperature and rainfall, as well as seasonal differences in day length that require animals to condense their daily routine into dramatically reduced daylight hours. Here we examine the effects of these climatic factors on the behavior (activity budgets and foraging patterns) and physiology (fecal glucocorticoid concentrations) of adult females (N = 33) in three groups of chacma baboons (Papio ursinus) inhabiting the Cape Peninsula, where temperatures ranged from 7 to 39 °C, monthly rainfall ranged from 2 to 158 mm, and day length varied by 4.5 h across seasons. Climatic variables showed a clear relationship to female baboon glucocorticoid concentrations, which significantly increased with lower temperatures, higher rainfall and shorter day lengths. Activity budgets also differed between summer and winter, with females generally spending less time socializing, moving and resting in the winter compared to summer, with some differences between troops in their feeding-related activities. Cold temperatures accompanied by rainfall and short day lengths may thus represent an ecological constraint for this population. This study highlights the potential impact of anthropogenic climate change on the physiology, behavior, and, ultimately, survival of wildlife populations.

Getting Humans Off Monkeys' Backs: Using Primate Acclimation as a Guide for Habitat Management Efforts

Wild primates face grave conservation challenges, with habitat loss and climate change projected to cause mass extinctions in the coming decades. As large-bodied Neotropical primates, mantled howling monkeys (Alouatta palliata) are predicted to fare poorly under climate change, yet are also known for their resilience in a variety of environments, including highly disturbed habitats. We utilized ecophysiology research on this species to determine the morphological, physiological, and behavioral mechanisms howlers employ to overcome ecological challenges. Our data show that howlers at La Pacifica, Costa Rica are capable of modifying body size. Howlers displayed reduced mass in warmer, drier habitats, seasonal weight changes, frequent within-lifetime weight fluctuations, and gradual increases in body mass over the past four decades. These within-lifetime changes indicate a capacity to modify morphology in a way that can impact animals' energetics and thermodynamics. Howlers are also able to consume foods with a wide variety of food material properties by altering oral processing during feeding. While this capability suggests some capacity to cope with the phenological shifts expected from climate change and increased habitat fragmentation, data on rates of dental microwear warn that these acclimations may also cost dental longevity. Lastly, we found that howlers are able to acclimate to changing thermal pressures. On shorter-term daily scales, howlers use behavioral mechanisms to thermoregulate, including timing activities to avoid heat stress and utilizing cool microhabitats. At the seasonal scale, animals employ hormonal pathways to influence heat production. These lines of evidence cumulatively indicate that howlers possess morphological, physiological, and behavioral mechanisms to acclimate to environmental challenges. As such, howlers' plasticity may facilitate their resilience to climate change and habitat loss. While habitat loss in the tropics is unlikely to abate, our results point to a potential benefit of active management and selective cultivation to yield large, interconnected forest fragments with targeted phenology that provides both a complex physical structure and a diversity of food sources. These steps could assist howlers in using their natural acclimation potential to survive future conservation threats.

Being hunted high and low: do differences in nocturnal sleeping and diurnal resting sites of howler monkeys (Alouatta nigerrima and Alouatta discolor) reflect safety from attack by different types of predator?

Predation risk is important in influencing animal behaviour. We investigated how the choice of nocturnal sleeping and diurnal resting sites by two species of primates was influenced by the most likely forms of attack (diurnal raptors and nocturnal felids). We recorded vertical and horizontal patterns of occupancy for 47 sleeping and 31 resting sites, as well as the presence of lianas or vines on trees. We compared the heights of trees used as resting or sleeping sites by the monkeys with those of 200 forest trees that the monkeys did not use. Trees used as nocturnal sleeping sites were taller than those used as diurnal resting sites, and taller than trees that the monkeys did not use. However, while trees used as diurnal resting sites were not significantly taller than non-used trees, diurnal resting sites were located on branches closer to the ground, closer to the main trunk of the tree and in trees with more lianas/vines than nocturnal sleeping sites. The differences in site location can be explained by the type of predator most likely to attack at a particular time: raptors in the day and felids at night.

Behavioral adjustments and support use of François' langur in limestone habitat in Fusui, China: Implications for behavioral thermoregulation

Climatic factors such as temperature and humidity vary seasonally in primate habitats; thus, behavioral adjustments and microhabitat selection by primate species have been interpreted as behavioral adaptations. François' langur (Trachypithecus francoisi), a native species to southwest China and northern Vietnam, inhabits a limestone habitat with extreme climatic conditions. To understand the potential effects of climatic seasonality on this species, we collected data on the individual behavioral budgets in a T. francoisi group between January and December 2010 in Fusui County, China. Monthly, we performed 5-11 days of observation during this period, using focal animal sampling and continuous recording methods. We also recorded ambient temperature (T a) and relative humidity (H r) data at our study site. Results indicated that T a and H r were significantly correlated with each other and fluctuated dramatically on a daily, monthly, and seasonal basis. The amount of time spent resting, grooming, basking, and huddling also varied on a daily, monthly, and seasonal basis. The proportion of resting time and total sedentary activity time significantly increased at high and low T as, respectively. The total sedentary time, resting time, and plant branch use all showed positive significant correlations with T a. Our results suggest that behavioral adjustment and support use of T. francoisi, at least partly, were related to thermoregulation. T. francoisi minimized thermal stress through behavioral adjustments and support use. It is an adaptive behavior associated with the climatic extremes of limestone habitat. This study can potentially advise conservation management strategies in this specific habitat. Conservation efforts should focus on vegetation restoration in langurs' habitat, including those in the foothills.

Tracking microhabitat temperature variation with iButton data loggers

PREMISE OF THE STUDY

Fine-scale variation in temperature and soil moisture contribute to microhabitats across the landscape, affecting plant phenology, distribution, and fitness. The recent availability of compact and inexpensive temperature and humidity data loggers such as iButtons has facilitated research on microclimates.

METHODS AND RESULTS

Here, we highlight the use of iButtons in three distinct settings: comparisons of empirical data to modeled climate data for rare rock ferns in the genus Asplenium in eastern North America; generation of fine-scale data to predict flowering time and vernalization responsiveness of crop wild relatives of chickpea from southeastern Anatolia; and measurements of extreme thermal variation of solar array installations in Vermont.

DISCUSSION

We highlight a range of challenges with iButtons, including serious limitations of the Hygrochron function that affect their utility for measuring soil moisture, and methods for protecting them from the elements and from human interference. Finally, we provide MATLAB code to facilitate the processing of raw iButton data.

Ambient temperature and humidity modulate the behavioural thermoregulation of a small arboreal mammal (Callicebus bernhardi)

Maintaining a constant body temperature is critical to the proper functioning of metabolic reactions. Behavioural thermoregulation strategies may minimize the cost of energetic balance when an animal is outside its thermoneutral zone. We investigated whether ambient temperature and relative air humidity influence the use of behavioural strategies by a group of Prince Bernhard's titi monkeys (Callicebus bernhardi) living in a forest fragment. We monitored a social group composed of four individuals (an adult couple and two juveniles) for 1010h from March to September 2015. We used the instantaneous scan sampling method to record the body posture, the microhabitat, and the occurrence of huddling with group mate(s) when animals were resting. We recorded ambient temperature and relative humidity in the shade every 10min with a data logger hanging at a height of approximately 5m. Daytime temperature ranged from 18.5°C to 38.5°C and relative humidity ranged from 21% to 97%. Titi monkeys avoided sunny places at higher temperatures, especially above 31°C. Minimum night temperature did not influence the choice of resting microhabitats during the first hour after sunrise. Sitting was the major resting posture during the day (62%). Titi monkeys increased the use of heat-dissipating postures at ambient temperatures >27°C. In addition, an increase in relative humidity increased the use of these postures at 26°C, 27°C, 29°C and 33°C, but caused a decrease at 24°C. On the other hand, the ambient temperature did not influence the occurrence of huddling. We conclude that microhabitat choice and postural behaviour are important for titi monkeys to prevent overheating and suggest that these behavioural adjustments might also be critical for other tropical arboreal mammals.