Basking behaviour in relation to energy use and food availability in one of the smallest marsupials

Although several mammals have been observed to bask in the sun, little is known about this behaviour or its energetic consequences. We investigated the importance of basking behaviour for one of the smallest marsupials, 'Planigale gilesi' (9 g). Metabolic rates of captive planigales (n = 6) exposed to simulated natural conditions with access to a radiant heat source were measured. Basking behaviour as a function of food availability was quantified using a video camera installed within the planigales' home cages (n = 7). All planigales basked during respirometry measurements, reducing resting energy expenditure by 58% at an ambient temperature of 15°C, which reflects conditions in their nesting sites in the wild during winter. Basking behaviour in home cages was displayed by all but one planigale; food withdrawal either triggered basking or it caused a significant increase in basking duration. Our study demonstrates the effectiveness of basking for reducing energy expenditure in one of the smallest marsupials, supporting recent findings on the importance of behavioural thermoregulation in small mammals in general.