Larger antelopes are sensitive to heat stress throughout all seasons but smaller antelopes only during summer in an African semi-arid environment

Heat stress can limit the activity time budget of ungulates due to hyperthermia, which is relevant for African antelopes in ecosystems where temperature routinely increases above 40 °C. Body size influences this thermal sensitivity as large bodied ungulates have a lower surface area to volume ratio than smaller ungulates, and therefore a reduced heat dissipation capacity. We tested whether the activity pattern during the day of three antelope species of different body size—eland, blue wildebeest and impala—is negatively correlated with the pattern of black globe temperature (BGT) during the day of the ten hottest days and each season in a South African semi-arid ecosystem. Furthermore, we tested whether the larger bodied eland and wildebeest are less active than the smaller impala during the hottest days and seasons. Our results show that indeed BGT was negatively correlated with the diurnal activity of eland, wildebeest and impala, particularly during summer. During spring, only the activity of the larger bodied eland and wildebeest was negatively influenced by BGT, but not for the smallest of the three species, the impala. We argue that spring, with its high heat stress, coupled with poor forage and water availability, could be critical for survival of these large African antelopes. Our study contributes to understanding how endothermic animals can cope with extreme climatic conditions, which are expected to occur more frequently due to climate change.     

Black wildebeest seek shade less and use solar orientation behavior more than do blue wildebeest

Many ungulates, including wildebeest, seek shade and orient their bodies relative to incoming solar radiation in order to reduce environmental heat loads. Blue (Connochaetes taurinus) and black wildebeest (Connochaetes gnou), which co-exist artificially in some reserves in South Africa, are thought to adopt different thermoregulatory behaviors to mitigate high environmental heat loads. However, whether or not blue and black wildebeest use different behaviors to reduce heat loads in regions where they co-occur has never previously been examined. We compared the shade seeking and solar orientation behavior of free-ranging blue and black wildebeest in summer at three locations in South Africa where both species co-occur. We found that blue wildebeest exhibited more shade seeking behavior than did black wildebeest at all times of day, at all study sites. Black wildebeest remained in the sun but were more likely than blue wildebeest to orient their bodies parallel to the sun at all study sites, a behavior which reduces the amount of surface area exposed to incoming radiation. Black wildebeest were most likely to employ parallel solar orientation during the hottest times of the day when the sun was not directly overhead (i.e., solar noon ± 1 hour). We thus demonstrate that co-occurring blue and black wildebeest use different thermoregulatory behaviors to reduce high heat loads. It is possible that the lack of shade in the historical distribution of black wildebeest led to selective pressure for reliance on solar orientation. Differences in thermoregulatory behavior can affect species-specific heat loads, habitat use, body mass, fitness and grazing activity. Such differences may also allow blue and black wildebeest to inhabit separate microclimates within the same habitat, provided there is sufficient heterogeneity in vegetation structure, potentially facilitating reproductive isolation.     

Orientation to solar radiation in black wildebeest (<Emphasis Type="Italic">Connochaetes gnou</Emphasis>)

We recorded the body axis orientation of free-living black wildebeest relative to incident solar radiation and wind. Observations were made on three consecutive days, on six occasions over the course of 1 year, in a treeless, predominantly cloudless habitat. Frequency of orientation parallel to incident solar radiation increased, and perpendicular to incident solar radiation decreased, as ambient dry-bulb temperature or solar radiation intensity increased, or wind speed decreased. We believe these changes were mediated via their effect on skin temperature. Parallel orientation behavior was more prominent when the wildebeest were standing without feeding than it was when they were feeding. We calculate that a black wildebeest adopting parallel orientation throughout the diurnal period would absorb 30% less radiant heat than the same animal adopting perpendicular orientation. Parallel orientation was reduced at times when water was freely available, possibly reflecting a shift from behavioral to autonomic thermoregulatory mechanisms. The use of orientation behavior by black wildebeest is well developed and forms part of the suite of adaptations that help them to maintain heat balance while living in a shadeless, often hot, environment.     

Meteorological weather station data can be used in climate matching studies of biological control agents

Meteorological weather station data are often used in climate matching studies to predict potential distributions of biological control agents, yet, this does not take into account the effects of microclimates experienced by the agents. Comparisons of the number of generations that the mirid, Eccritotarsus catarinensis, a biological control agent of water hyacinth, Eichhornia crassipes (Mart.) Solms-Laub (Pontederiaceae), was predicted to complete using meteorological weather station data, on site air temperature and water hyacinth canopy microclimate temperatures recorded over two years showed that there were no significant differences between the temperature data sources. Therefore, meteorological weather station data used in degree-day models of biological control agents are useful in explaining broad establishment patterns.     

Effects of Relatedness,Dominance, Age,and Association on Reciprocal Allogrooming by Captive Impala

Wild impala display a highly reciprocal allogrooming system that, by virtue of its frequency and high degree of reciprocity, is unique among ungulates. A herd of 35 free-ranging captive impala provided opportunity to examine the degree of reciprocity of allogrooming exchanges and the influence of relatedness, dominance, age and association on partner preferences and distribution of grooming between allogrooming partners. As in wild impala, the exchange of allogrooming bouts in the captive impala was highly reciprocal regardless of partners. Kinship and dominance had no influence on partner preference or distribution of grooming between partners. Although mothers showed a significant preference to allogroom with their unweaned offspring, this preference practically disappeared with older offspring. Age-mates (no greater than 6 mo apart) tended to associate with one another and spatial proximity was positively correlated with grooming partner preference. It was not clear whether impala actively sought out age-mates for grooming, or randomly chose grooming partners from nearby age-mates. The failure to find a role for kinship and dominance is counter to what has generally been found in most Old World terrestrial primate studies. The absence of pronounced social influences, coupled with the known effectiveness of grooming in removing ectoparasites, suggest that a utilitarian role, especially removal of ticks, is an important function of the impala reciprocal allogrooming system.     

The Importance of Biologically Relevant Microclimates in Habitat Suitability Assessments

Predicting habitat suitability under climate change is vital to conserving biodiversity. However, current species distribution models rely on coarse scale climate data, whereas fine scale microclimate data may be necessary to assess habitat suitability and generate predictive models. Here, we evaluate disparities between temperature data at the coarse scale from weather stations versus fine-scale data measured in microhabitats required for a climate-sensitive mammal, the American pika (Ochotona princeps). We collected two years of temperature data in occupied talus habitats predicted to be suitable (high elevation) and unsuitable (low elevation) by the bioclimatic envelope approach. At low elevations, talus surface and interstitial microclimates drastically differed from ambient temperatures measured on-site and at a nearby weather station. Interstitial talus temperatures were frequently decoupled from high ambient temperatures, resulting in instantaneous disparities of over 30°C between these two measurements. Microhabitat temperatures were also highly heterogeneous, such that temperature measurements within the same patch of talus were not more correlated than measurements at distant patches. An experimental manipulation revealed that vegetation cover may cool the talus surface by up to 10°C during the summer, which may contribute to this spatial heterogeneity. Finally, low elevation microclimates were milder and less variable than typical alpine habitat, suggesting that, counter to species distribution model predictions, these seemingly unsuitable habitats may actually be better refugia for this species under climate change. These results highlight the importance of fine-scale microhabitat data in habitat assessments and underscore the notion that some critical refugia may be counterintuitive.     

Alteration in diel activity patterns as a thermoregulatory strategy in black wildebeest (<Emphasis Type="Italic">Connochaetes gnou</Emphasis>)

The nychthemeral activity patterns of a population of female black wildebeest inhabiting a shadeless environment were surveyed periodically over 1 year. The wildebeest fed mostly at night, with the proportion of feeding at night increasing when ambient conditions were hotter. Inactive periods were spent mostly lying during cooler weather but standing as days became hotter. We suggest that the entire suite of behavioural adjustments is beneficial to heat exchange with the environment. Behaviour patterns were markedly different during one warm weather survey, from the other warm weather surveys, when an 8-month dry spell had just been broken. We suggest that this may reflect the availability of water for autonomic thermoregulation, a consequent decreased reliance on behavioural thermoregulation, and a release of the thermal constraints on foraging. Our results help to explain the ability of black wildebeest to maintain body core temperature within a very narrow range despite being exposed to an environment with large nychthemeral variations in thermal conditions and offering little in the way of microclimate selection.     

Activity re-assignment and microclimate selection of free-living Arabian oryx: responses that could minimise the effects of climate change on homeostasis?

Predicting whether behaviour could buffer the effects of climate change on long-lived mammals requires a better understanding of the long-term behavioural responses of mammals to environmental stress. Using biologging, we measured locomotor activity and microclimate selection, over eight months, in five Arabian oryx (Oryx leucoryx) living free in a Saudi Arabian desert. The oryx displayed seasonal flexibility in activity patterns, shifting from a continuous 24-h activity pattern with crepuscular peaks in cooler months to a predominantly nocturnal activity pattern during the hottest months, without reducing the total 24-h activity level. The proportion of total 24-h activity that occurred during daylight hours was just 29 ± 8% during the hottest months, versus 53 ± 8% (mean ± SD, n = 5 oryx) in the other months. The attenuation in diurnal activity levels during the hot months was accompanied by the selection of cooler microclimates, presumably via shade seeking, during the heat of the day. Analysis of miniature black globe (miniglobe) temperature from a remote sensor on the collar of two female animals revealed that oryx selected microclimates cooler than the microclimates in direct sun at higher environmental heat loads across all periods, but with enhanced efficiency during the dry periods. We have quantified activity re-assignment and microclimate selection as responses to hot arid conditions in a free-living artiodactyl. Such flexible behavioural processes may act to buffer the adverse effects of the progressively hotter and drier conditions predicted to occur with climate change.     

Reciprocal Allogrooming in Dam-reared and Hand-reared Impala Fawns

Among adult females and males of African antelope impala are unique in their performance of reciprocal allogrooming. The occurrence of this behaviour in neonatal impala fawns was explored in a free-ranging impala herd at the San Diego Wild Animal Park where 5 dam-reared fawns were observed from birth through 10 weeks of age. One-way maternal grooming and reciprocal allogrooming with the dam and non dam partners emerged as distinct behavioural systems. Maternal grooming, directed mostly to the anogenital area, was typical of that seen in other ungulates, and sharply declined over the first two weeks. Reciprocal allogrooming, characterized by alternate exchanges of grooming bouts with a partner in the same manner as in adults, was seen as early as 3–8 d after birth. All fawns were grooming with unrelated adult females by the end of the second week. By week 2 virtually every measure of reciprocal allogrooming by fawns (grooming delivered per hour, reciprocity, and percent of encounters initiated) was as high as for adults. The appearance of this reciprocal allogrooming pattern, especially at such an early age, appears to be unique among ungulates, and possibly mammals in general. Three hand-reared impala fawns, deprived of the opportunity to interact with older herdmates, but having access to impala fawns and heterospecific fawns, were observed from 1–3 mo of age. The hand-reared impala showed no alteration in the occurrence of reciprocal allogrooming behaviour compared with the dam-reared control fawns, indicating that allogrooming experience with older animals was not required for the appearance of reciprocal allogrooming at an early age. Interestingly, hand-reared fawns persisted in grooming heterospecific fawns despite the fact that heterospecifics rarely reciprocated grooming. We postulate that the strong predisposition for impala young to groom others may be related to the threat of tick infestation in the impala's ecotone habitat.     

Hyperthermia in captured impala (Aepyceros melampus): a fright not flight response

To investigate the patterns and mechanisms of capture-induced hyperthermia, we surgically implanted 26 impala (Aepyceros melampus) with miniature thermometric data loggers, which measured body temperatures continuously throughout capture procedures. Four groups of impala, which were habituated to varying levels of handling and boma-housing, were captured by net restraint or by chemical immobilization. The study took place between July 1999 and December 2005. Irrespective of whether impala were chemically captured, net-captured, or disturbed by exposure to a stressor, they developed a precipitous increase in body temperature. This increase in body temperature was not related to activity levels; animals that had low activity levels before immobilization had larger increases in body temperature compared to those that had high activity levels but were not immobilized (t = 3.6, P = 0.001, n = 5). Similarly this increase in body temperature was not related to environmental heat load at the time of darting and immobilization (r = -0.05, P = 0.85). Body temperature increase also did not depend on whether the animals were captured using drugs or not. However, we found that those animals that were habituated more to handling and boma-housing had smaller increases in body temperatures (F = 37, P<0.001) and smaller stress responses, indicated by lower plasma cortisol concentrations (F = 5.5, P<0.05), and less fractious behavior, compared to those animals that were habituated less or not at all. Therefore we believe that capture-induced hyperthermia in impala is caused predominantly by stress, which induces a rapid rise in body temperature.     

Redefining physiological responses of moose (Alces alces) to warm environmental conditions

We tested the concept that moose (Alces alces) begin to show signs of thermal stress at ambient air temperatures as low as 14 °C. We determined the response of Alaskan female moose to environmental conditions from May through September by measuring core body temperature, heart rate, respiration rate, rate of heat loss from exhaled air, skin temperature, and fecal and salivary glucocorticoids. Seasonal and daily patterns in moose body temperature did not passively follow the same patterns as environmental variables. We used large changes in body temperature (≥1.25 °C in 24hr) to indicate days of physiological tolerance to thermal stressors. Thermal tolerance correlated with high ambient air temperatures from the prior day and with seasonal peaks in solar radiation (June), ambient air temperature and vapor pressure (July). At midday (12:00hr), moose exhibited daily minima of body temperature, heart rate and skin temperature (difference between the ear artery and pinna) that coincided with daily maxima in respiration rate and the rate of heat lost through respiration. Salivary cortisol measured in moose during the morning was positively related to the change in air temperature during the hour prior to sample collection, while fecal glucocorticoid levels increased with increasing solar radiation during the prior day. Our results suggest that free-ranging moose do not have a static threshold of ambient air temperature at which they become heat stressed during the warm season. In early summer, body temperature of moose is influenced by the interaction of ambient temperature during the prior day with the seasonal peak of solar radiation. In late summer, moose body temperature is influenced by the interaction between ambient temperature and vapor pressure. Thermal tolerance of moose depends on the intensity and duration of daily weather parameters and the ability of the animal to use physiological and behavioral responses to dissipate heat loads.     

Body temperature variation of South African antelopes in two climatically contrasting environments

To understand the adaptive capacity of a species in response to rapid habitat destruction and climate change, we investigated variation in body temperature (T_b) of three species of antelope, namely eland, blue wildebeest and impala, using abdominally-implanted temperature data loggers. The study was conducted at two climatically contrasting environments in South Africa, one with a less seasonal and mild winter (Mapungubwe National Park) and the other with a more seasonal, long and cold winter (Asante Sana Game Reserve). Since the habitat with long and cold winters would be suboptimal for these African antelopes, which evolved in less seasonal and hot environments, antelopes in Asante Sana were expected to exhibit a larger amplitude in T_b and a lower minimum body temperature (Min T_b) during winter to reduce T_b and the ambient temperature (T_b−T_a) gradient to save energy. In both eland and impala, 24-h body temperature amplitude did not differ between the study sites, regardless of season. Conversely, wildebeest in Mapungubwe showed a higher variability in the 24-h amplitude of body temperature and also a lower Min T_b during winter and spring than the wildebeest in Asante Sana. This variation in T_b among Mapungubwe wildebeest was influenced by both the amplitude of ambient temperature (positive) and cumulative rainfall (negative), which was not the case for wildebeest in Asante Sana. We propose that the low Min T_b of wildebeest in Mapungubwe was the result of nutritional stress during winter and spring; an evident response even during a year of average rainfall. Therefore, these wildebeest apparently live in a physiologically stressful environment. With the predicted increase in the frequency and intensity of drought periods in southern Africa, wildebeest and other grazers, will likely experience greater nutritional stress in the future.     

Does size matter? Comparison of body temperature and activity of free-living Arabian oryx (<Emphasis Type="Italic">Oryx leucoryx</Emphasis>) and the smaller Arabian sand gazelle (<Emphasis Type="Italic">Gazella subgutturosa marica</Emphasis>) in the Saudi desert

Heterothermy, a variability in body temperature beyond the normal limits of homeothermy, is widely viewed as a key adaptation of arid-adapted ungulates. However, desert ungulates with a small body mass, i.e. a relatively large surface area-to-volume ratio and a small thermal inertia, are theoretically less likely to employ adaptive heterothermy than are larger ungulates. We measured body temperature and activity patterns, using implanted data loggers, in free-ranging Arabian oryx (Oryx leucoryx, ±70 kg) and the smaller Arabian sand gazelle (Gazella subgutturosa marica, ±15 kg) inhabiting the same Arabian desert environment, at the same time. Compared to oryx, sand gazelle had higher mean daily body temperatures (F _1,6 = 47.3, P = 0.0005), higher minimum daily body temperatures (F _1,6 = 42.6, P = 0.0006) and higher maximum daily body temperatures (F _1,6 = 11.0, P = 0.02). Despite these differences, both species responded similarly to changes in environmental conditions. As predicted for adaptive heterothermy, maximum daily body temperature increased (F _1,6 = 84.0, P < 0.0001), minimum daily body temperature decreased (F _1,6 = 92.2, P < 0.0001), and daily body temperature amplitude increased (F _1,6 = 97.6, P < 0.0001) as conditions got progressively hotter and drier. There were no species differences in activity levels, however, both gazelle and oryx showed a biphasic or crepuscular rhythm during the warm wet season but shifted to a more nocturnal rhythm during the hot dry season. Activity was attenuated during the heat of the day at times when both species selected cool microclimates. These two species of Arabian ungulates employ heterothermy, cathemerality and shade seeking very similarly to survive the extreme, arid conditions of Arabian deserts, despite their size difference.     

Energy advantages of orientation to solar radiation in three African ruminants

Animal orientation relative to incident solar radiation allows an animal to effectively adjust the amount of radiant heat gained from an environment. Yet recent literature found ruminants to primarily orientate north/south and proposed magnetic alignment as the most parsimonious explanation. To test whether such northerly orientation has an energy advantage, we used heated cylindrical models to estimate energy costs of thermoregulation associated with north and east orientations of three species of African ruminants under cool winter conditions. Concurrent behavioural observations revealed that eland, blue wildebeest and impala did not preferentially orientate north/south during warm summer or cool winter conditions. Instead, all three species preferred to orientate perpendicular to incident solar radiation during winter and parallel to incident solar radiation during summer, throughout the day. On clear winter days with little wind, more than 60% of animal orientation preference could be accounted for by the energy savings associated with that orientation. Thus energy demands are likely to be the primary driver of animal orientation preferences.     

Microhabitats in the tropics buffer temperature in a globally coherent manner

Vegetated habitats contain a variety of fine-scale features that can ameliorate temperate extremes. These buffered microhabitats may be used by species to evade extreme weather and novel climates in the future. Yet, the magnitude and extent of this buffering on a global scale remains unknown. Across all tropical continents and using 36 published studies, we assessed temperature buffering from within microhabitats across various habitat strata and structures (e.g. soil, logs, epiphytes and tree holes) and compared them to non-buffered macro-scale ambient temperatures (the thermal control). Microhabitats buffered temperature by 3.9°C and reduced maximum temperatures by 3.5°C. Buffering was most pronounced in tropical lowlands where temperatures were most variable. With the expected increase in extreme weather events, microhabitats should provide species with a local layer of protection that is not captured by traditional climate assessments, which are typically derived from macro-scale temperatures (e.g. satellites). Our data illustrate the need for a next generation of predictive models that account for species'' ability to move within microhabitats to exploit favourable buffered microclimates.     

Protozoa and digestive tract parameters in Blue wildebeest (Connochaetes taurinus) and Black wildebeest (Connochaetes gnou), with description of Entodinium taurinus n. sp.

Rumen contents from four blue wildebeest (Connochaetes taurinus) and six black wildebeest (Connochaetes gnou) were collected from two locations during two winter culling seasons. A total of 16 species of protozoa were found in blue wildebeest with Dasytricha ruminantium, Opisthotrichum janus and Ostracodinium gracile occurring in all four animals. In black wildebeest, 23 species of protozoa were observed with only Diplodinium bubalidis (caudal spine morphotype) and Ostracodinium damaliscus being present in all animals. In the blue wildebeest, the total number of species in an individual animal varied from 9 to 11 and in the black wildebeest, the number ranged from 4 to 14. Concentrations of cells per ml ranged from 1110 to 5880 in the blue wildebeest and 3120 to 6240 in the black wildebeest. This study is the first report on protozoa species in the blue and black wildebeest. A new species of Entodinium is described, Entodinium taurinus n. sp., observed in the rumen contents of three blue wildebeest. Several physical parameters of the digestive tract were also measured, including distribution, pH and density of gastrointestinal contents in different sections of the total tract. In vitro gas production was estimated for rumen, cecum and colon contents.     

Antipredator behaviour of African ungulates around human settlements

As human populations grow and come into more frequent contact with wildlife, it is important to understand how anthropogenic disturbance alters wildlife behaviour. Using fine‐scale spatial analyses, we examined how proximity to human settlements affects antipredator responses of ungulates. We studied seven common ungulate species (Kirk's dik‐dik, Thomson's gazelle, impala, common warthog, common wildebeest, common zebra and Masai giraffe) in the Tarangire–Manyara ecosystem in northern Tanzania. In zebra and giraffe, flight responses to humans were significantly more likely when closer to settlements; however, there was a weak relationship between flight responses and distance to settlement in all other species. While there was largely a weak relationship between proximity to human settlements, the distribution of settlements in the landscape appears to affect wildlife behaviour, suggesting that animals perceive and respond to spatial variation in risk exerted by humans.     

The Role of the Plumage in Heat Transfer Processes of Birds

The plumage of birds provides a critical thermal buffer betweenthe animal and its environment. Rates of energy expenditureare strongly influenced by the thermal properties of the environmentor the microclimates the animal occupies. Current data suggestthat the addition of solar radiation is equivalent to threeto four-fold changes in wind speed and that solar heat gaincan be extremely sensitive to changes in wind speed. Dry heat transfer through the plumage occurs by three avenues1) conduction and free convection through air 2) conductionalong the solid elements of the plumage and 3) radiation. Overall,about 95% of the total heat flow is evenly divided between thefirst two avenues. Radiative heat transfer accounts for onlyabout 5% of total heat flow. Plumage color, as well as the microstructureand micro-optical properties of plumage elements, when combinedwith environmental properties (e.g., wind speed), determinethe radiative heat loads that birds acquire from solar radiation.Although plumage color or reflectivity determines the fractionof incident solar radiation that is absorbed by the plumageand generates heat, the fraction of this heat that contributesto the thermal load on the animal can vary greatly. In a fibrouscoat such as a plumage, there is some variable penetration intothe coat, with absorption over a range of coat depths. Factorssuch as feather micro-optics and structure are critical determinantsof radiation penetration into avian coats. Significant differencesin solar heat loads can also result from behavioral adjustmentsin plumage thickness.     

Thermal biology,torpor and behaviour in sugar gliders: a laboratory-field comparison

Most studies on animal physiology and behaviour are conducted in captivity without verification that data are representative of free-ranging animals. We provide the first quantitative comparison of daily torpor, thermal biology and activity patterns, conducted on two groups of sugar gliders (Petaurus breviceps, Marsupialia) exposed to similar thermal conditions, one in captivity and the other in the field. Our study shows that activity in captive gliders in an outdoor aviary is restricted to the night and largely unaffected by weather, whereas free-ranging gliders omit foraging on cold/wet nights and may also forage in the afternoon. Torpor occurrence in gliders was significantly lower in captivity (8.4% after food deprivation; 1.1% for all observations) than in the field (25.9%), mean torpor bout duration was shorter in captivity (6.9 h) than in the field (13.1 h), and mean body temperatures during torpor were higher in captivity (25.3°C) than in the field (19.6°C). Moreover, normothermic body temperature as a function of air temperature differed between captive and free-ranging gliders, with a >3°C difference at low air temperatures. Our comparison shows that activity patterns, thermal physiology, use of torpor and patterns of torpor may differ substantially between the laboratory and field, and provides further evidence that functional and behavioural data on captive individuals may not necessarily be representative of those living in the wild.     

Estimating density of Kirk’s dik‐dik (Madoqua kirkii Günther), impala (Aepyceros melampus Lichtenstein) and common zebra (Equus burchelli Gray) at Mpala,Laikipia District,Kenya

This study compares two methods of estimating the density of three ungulate species: Kirk’s dik‐dik, impala and common zebra, in a dry savannah ecosystem. Fixed strip width and distance sampling involving direct animal counts were used in parallel, and tested for bias and precision in two habitats. Distance sampling was the method that achieved a better balance between accuracy and precision. The differences in sightability of ungulates, according to body size, colour and habitat characteristics, are taken into account by the distance sampling method, but not by the strip method, which produced, what we suspect are, underestimates of animal density.