Water use and the thermoregulatory behaviour of kangaroos in arid regions: insights into the colonisation of arid rangelands in Australia by the Eastern Grey Kangaroo (Macropus giganteus)

Abstract

The Eastern Grey Kangaroo (Macropus giganteus) occurs mostly in the wetter regions of eastern Australia. However, in the past 30-40 years it has moved into more arid regions (rainfall < 250 mm), thus increasing its overlap zone with the xeric adapted Red Kangaroo (Macropus rufus). An increased access to water (supplied for domestic stock) may explain this range extension, but changes in the availability of preferred feed could also be involved. The water use, drinking patterns and thermoregulatory behaviour of these two species of kangaroo have been examined in a semi-free range study, during summer at an arid rangeland site. Foraging was largely nocturnal in both species and during the day they behaved to reduce heat loads. This was especially so for M. giganteus, which showed greater shade seeking. However, it still used more water (72 +/- 2.6 mL kg(-1) day(-1), mean +/- SE) than M. rufus (56 +/- 7.6 mL kg(-1) day(-1)) and drank twice as frequently. Although M. giganteus produced a less concentrated urine (1422 +/- 36 mosmol kg(-1)) than M. rufus (1843 +/- 28 mosmol kg(-1)), kidney physiology did not explain all of the differences in water metabolism between the species. Water from the feed and faecal water retention also appear to be involved. Broadly, a better access to reliable water and the utilisation of mesic microhabitats has enabled M. giganteus to make inroads into the changing rangelands of eastern Australia. However, changes in the vegetation, due to stock grazing, have also favoured M. giganteus, which is a grass eating specialist.

Minimum daily core body temperature in western grey kangaroos decreases as summer advances: a seasonal pattern, or a direct response to water, heat or energy supply?

“…, or approximately 4% of the daily water turnover, if turnover is similar to that of the eastern grey kangaroo in summer (Dawson et al, 2006). If prolonged water deprivation was a characteristic of the habitat of western grey kangaroos, then a 4% water savings per day could improve the survival of individuals.…”

“…But in the reserve where the studies were conducted, water was available freely, so presumably the kangaroos had no need to conserve water. There are no data on drinking frequency in western grey kangaroos, but the closely related eastern grey kangaroo drinks at least every second day (Dawson et al, 2006). We have now measured T c in free ranging kangaroos over two spring-summer seasons and report the structure of the nychthemeral T c cycle and the effect of changes in environmental conditions on that cycle.…”

Artificial water points facilitate the spread of an invasive vertebrate in arid Australia

“…Although many desert vertebrates obtain all or most of their water requirements through their food or store water during periodic rainfall events, other animals that live in arid environments must have regular access to water (Withers ; Whitford ; Dawson et al . ).…”

Excluding access to invasion hubs can contain the spread of an invasive vertebrate

“…For example, the provision of AWPs in arid environments has been linked to range expansions and/or population increases of water birds and wild herbivorous mammals that must drink [16,17] and has provided previously unavailable habitat for aquatic organisms [18,19]. Thus, AWPs can influence how arid ecosystems function by facilitating the trophic and competitive interactions of species that need to access water to survive [20,21].…”