Thermoregulatory behaviour of ungulates in National Zoological Gardens of South Africa
M.L. Pitswane ¹
¹Department of Zoology and Entomology, University of Pretoria, Pretoria, South Africa
Abstract
Ungulates that inhibit desert areas have evolved behavioural strategies and morphological adaptations to aid thermoregulation. Using thermocouples, ambient temperature in the sun and shade was measured around seven ungulate species, the Arabian oryx, gemsbok, hogdeer, Scimitar-horned oryx, blackbuck, springbuck, and the impala. Experimental protocol was conducted on captive animals of the National Zoological Gardens of South Africa. We found that temperature increased with time across all species as the day progressed. Animals orientated perpendicular to the sun in the mornings, and parallel in the late mornings to noon. The study showed that ungulates exhibit thermoregulatory behaviours in relation to variation in ambient temperature, and that behaviour of these species cab be related to the habitat to which they are adapted.
- Introduction
Animals exhibit physiological plasticity to cope with daily and seasonal variations in ambient temperature within their environment (Garland and Adolph, 1991). Ungulates typically inhabit semi-arid to arid environments. They are broadly distributed, and because of this, they exhibit a range of physiological patterns for temperature and water regulation (Yousef, 1976). When body temperatures are higher than ambient temperatures, animals lose heat to the environment passively by radiation, convection, and conduction (Mitchell, 1977). However, these ungulates have different morphological adaptations of which can be thought to be related to the wide range of environmental pressures they encounter. A major morphological characteristic that regulates heat gain and water loss in all animals is body size and shape (Cain III et.al 2006). Large-bodied animals in gain heat from the environment at a slower rate than do smaller animals because of the surface-to-volume ratio and higher thermal inertia (Phillips and Heath 1995). Desert adapted ungulates typically have glossy, light-coloured pelage, which reflects more radiation than dark-coloured pelage (Finch 1972).
Behaviours of desert ungulates that aid thermoregulation in ungulates include timing of activity, diet selection, use of microhabitats, social behaviours, body orientation, migration, and timing of reproduction (Sargeant et.al 1994). In this study we look closely at timing of activity and body orientation.
The hypotheses we are aiming to address in this study are (1) ungulates exhibit thermoregulatory behaviours in relation to variation in ambient temperature and (2) thermoregulatory behaviour of ungulate species is related to the habitat to which they are adapted.
- Methods and Materials
The experiment was conducted at the National Zoological Gardens of South Africa (25.7383° S, 28.1892° E) which is located in Pretoria.
Our study species involved the Arabian oryx (Oryx leucoryx, Family Bovidae, Pallas, 1777) gemsbok (Oryx gazelle, Family Bovidae, Linnaeus, 1758), hogdeer (Axis porcinus, Family Cervidae, Zimmermann, 1780), Scimitar-horned oryx (Oryx dammah, Family Bovidae, Cretzschmar, 1826), blackbuck (Antilope cervicapra, Family Bovidae, Linnaeus, 1758), springbuck (Antidorcas marsupialis, Family Bovidae, Zimmermann, 1780), and the impala (Aepyceros melampus, Family Bovidae, Lichtenstein, 1812).
Using thermocouples () we measured ambient temperature in the sun and in the shade. The number of individuals of each representative species was also taken into account, along with orientation to the sun and behaviour (grazing, standing, etc.). Temperature measurements took place early to late morning between 9am-11am.
- Results
Ambient temperature increased as the day progressed, from 14.1 ± 1.9 ºC in the early morning to 19.1 ± 2.5 ºC in the late mornings for readings recorded in the sun. Whereas, ambient temperature recorded in shade ranged from 12.6 ± 1.6ºC to 15.8 ± 2.0ºC on average. Early mornings we found that more individuals in all species were in the sun than in shade, and as the day progresses, the number of individuals in the shade increased as well. In addition, most of the animals were orientated perpendicular to the sun during early mornings. The orientation tends to change to parallel as the day goes on. Those individuals that were in the sun would be mostly standing, only a few grazing, and very few lying down or running. Those individuals that were seen in shade were mostly grazing, lying down, walking about and very few standing.
- Discussion
The Arabian oryx, gemsbok, and the Scimitar-horned oryx are all from genus Oryx. These species are desert adapted. They have horns of which assist in heat dissipation during the extreme temperatures they are exposed to. They are grazers and do not have access to much excess water in their natural habitat. Thus, they number one priority is water conservation. To compensate, they eat a lot as we have seen in this study how majority of the individuals were grazing throughout the experiment. The study also found that the Oryx were always perpendicular to the sun in the mornings. Orientating the boy perpendicular to the sun maximizes heat gain, whereas parallel orientation minimizes heat gain.
Hog deer is the species from family cervidae of the experimental species of this study. It also originates from Southeast Asia mostly in grassland associated with rivers. And as such its thermoregulation capabilities is slightly different from that of all the other experimental species of which are all from family bovidae. In addition to that, it has a darker pelage than all of them, and we found that during the experiment it was mostly in shade, perhaps because the temperature was too much for it. In support, according to Gloger’s rule, within a species, more heavily pigmented forms tend to be found in more humid environments, e.g. near the equator.
Springbuck orientate themselves perpendicular to the sun, and the brown areas enhance heat absorption. In the middle of the day, they orientate themselves parallel to the sun and their white areas reflect short wave radiation (Louw 1993). However, we found the opposite during our study. The springbuck orientation in the late mornings was perpendicular to the sun. One reason could be because the late mornings were not as hot as one would have expected. Obtaining data from impalas was a mission because they were very active and always running.
- References
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Yousef, M. K. 1976. Thermoregulation in wild ungulates. Pages 108–122 in H.D. Johnson, editor. Progress in animal biometeorology: the effect of weather and climate on animals. Volume 1. Swets and Zeitlinger, Amsterdam, Netherlands.
Finch, V. A. 1972a. Thermoregulation and heat balance of the East African eland and hartebeest. American Journal of Physiology 222:1374–1379.
Finch, V. A. 1972b. Energy exchanges with the environment of two east African antelopes, the eland and the hartebeest. Symposia of the Zoological Society of London 31:315–326.
Sargeant, G. A., L. E. Eberhardt, and J. M. Peek. 1994. Thermoregulation by mule deer (Odocoileus hemionus) in arid rangelands of southcentral Washington. Journal of Mammalogy 75:536–544.
Garland, T., Jr., and S. C. Adolph. 1991. Physiological differentiation of vertebrate populations. Annual Review of Ecology and Systematics 22:193-228.
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