title: 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) andM. 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. fuliginosusspent more time thanM. rufusin 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. rufustolerated 19°C higher radiant temperatures thanM. fuliginosus(89°C versus 70°C radiant temperature). Across Australia, we predictedM. fuliginosusto be more restricted to shade thanM. rufus, with higher absolute shade requirements farther north. These results corroborate previous findings thatM. rufusis more adept at dealing with heat thanM. fuliginosusand indicate thatM. rufusis less dependent on shade on a continental scale.
authors.affiliation: School of BioSciences, The University of Melbourne , Melbourne Victoria, Australia.
authors.forename: J A
authors.initials: JA
authors.lastname: Roberts
authors.affiliation: School of BioSciences, The University of Melbourne , Melbourne Victoria, Australia.
authors.forename: G
authors.initials: G
authors.lastname: Coulson
authors.affiliation: School of Biological, Earth, and Environmental Sciences, The University of New South Wales, New South Wales, Australia; Faculty of Veterinary Sciences, The University of Sydney, New South Wales, Australia.
authors.forename: A J
authors.initials: AJ
authors.lastname: Munn
authors.affiliation: School of BioSciences, The University of Melbourne , Melbourne Victoria, Australia.
authors.forename: M R
authors.initials: MR
authors.lastname: Kearney
keywords: activity budget; endotherm; marsupial; range limits; shade-seeking behavior; temperature tolerance; thermoregulation; time budget