A continent-wide analysis of the shade requirements of red and western grey kangaroos

Abstract

Foraging time may be constrained by a suite of phenomena including weather, which can restrict a species' activity and energy intake. This is recognized as pivotal for many species whose distributions are known to correlate with climate, including kangaroos, although such impacts are rarely quantified. We explore how differences in shade seeking, a thermoregulatory behavior, of 2 closely-related kangaroo species, Macropus rufus (red kangaroos) and M. fuliginosus (western grey kangaroos), might reflect differences in their distributions across Australia. We observed foraging and shade-seeking behavior in the field and, together with local weather observations, calculated threshold radiant temperatures (based on solar and infrared radiant heat loads) over which the kangaroos retreated to shade. We apply these calculated tolerance thresholds to hourly microclimatic estimates derived from daily-gridded weather data to predict activity constraints across the Australian continent over a 10-year period. M. fuliginosus spent more time than M. rufus in the shade (7.6 ± 0.7 h versus 6.4 ± 0.9 h) and more time foraging (11.8 ± 0.5 h vs. 10.0 ± 0.6 h), although total time resting was equivalent (∼8.2 h). M. rufus tolerated 19°C higher radiant temperatures than M. fuliginosus (89°C versus 70°C radiant temperature). Across Australia, we predicted M. fuliginosus to be more restricted to shade than M. rufus, with higher absolute shade requirements farther north. These results corroborate previous findings that M. rufus is more adept at dealing with heat than M. fuliginosus and indicate that M. rufus is less dependent on shade on a continental scale.

The anterior nasal region in the Red Kangaroo (Macropus rufus) suggests adaptation for thermoregulation and water conservation

“…The comparative observations of M. robustus and M. fuliginosus support this observation. On the one hand, M. fuliginosus had a very low abundance of submucosal blood vessels in the lateral wall of the anterior nasal cavity, reflecting a lower requirement for evaporative nasal cooling in their typically more mesic distribution and their more shaded microhabitat selection when in more arid regions (Dawson, ; Munn et al ., ; Roberts et al ., ). On the other hand, M. robustus , which has a similar geographic distribution to M. rufus despite differences in microhabitat use, had very abundant submucosal vasculature within the lateral wall of the nasal cavity, and their daily water use is comparable between these species (Dawson et al ., ).…”

“…Within the arid zone, the distribution of grey kangaroos, M. fuliginosus and M. giganteus , is typically dependent on artificial water sources (Dawson et al ., ). Further, where overlap in distribution with the Red Kangaroo, M. rufus , occurs, M. fuliginosus and M. giganteus demonstrate higher specificity in microhabitat selection during the hottest periods, utilizing erosion gullies and tree outcrops for shelter (Dawson et al ., ; Munn et al ., ; Roberts et al ., ). The suite of adaptations that facilitate lower dependency on free‐water in M. rufus is not fully understood, but is known to include attributes associated with water economy in kidney physiology and gut reabsorption of water from feed and faeces (Freudenberger & Hume, ; Hume, ; Dawson, ).…”

Town roo, country roo: a comparison of behaviour in eastern grey kangaroos Macropus giganteus in developed and natural landscapes

“…Furthermore, the higher temperatures at the developed site may have caused kangaroos to seek out shade more frequently. Western grey kangaroos Macropus fuliginosus have been shown to have a low tolerance for being in direct sunlight during high temperatures and it is likely to be similar for eastern grey kangaroos as they have similar habitat requirements (Roberts et al 2016).…”

Towards a mechanistic understanding of the responses of large terrestrial mammals to heat and aridity associated with climate change

“…Similarly, despite being about four-fold smaller in size than Arabian oryx, Arabian sand gazelles (Gazella subgutturosa marica) in the same desert environment as the oryx sought shade at the same globe temperature (28°C) as did the oryx [96]. Red and western grey (Macropus fuliginosus) kangaroos of similar body mass retreated to shade at different radiant heat loads, with red kangaroos apparently more tolerant of radiant heat [97]. The data available to date therefore imply that the relationship between body mass and shade-seeking will not be a simple one.…”