Seasonal and depth-dependent thermoregulatory benefits of burrows for wombats – The largest burrowing marsupials

Mammals use burrows to behaviourally thermoregulate, save water, and avoid predation. The advantages of burrows vary not only seasonally but also with burrow depth. To quantify these effects, we used biophysical ecological models, which predict an animal's energetic and hydric costs within a characterised microclimate. For Australia's three extant wombat species, we quantified variation in the energetic advantage of burrows spatially, temporally, and with burrow depth. We simulated resting wombats with different traits (e.g., body size, fur) in different microclimates (above ground and burrows of varying depth) at six sites across Australia, two for each wombat species, over five years (1980, 1990, 2000, 2010, 2020). We assessed time spent within their thermoneutral zone-heat production equals heat loss thus minimising energy and water expenditure -and frequency of extreme heat stress (i.e., no viable hydric solution for the conditions stipulated). Our findings show that burrows are essential for reducing energetic and hydric costs and for survival during the hottest season in areas with no shade, e.g., the semi-arid zone. We found no evidence that extreme heat stress has increased temporally i.e., due to climate change, but it was frequently predicted in shallow burrows in 2020, having rarely been previously forecast. For energy requirements, we found lower thermoregulatory costs for deeper burrows in the cold season and for shallow burrows in the hot season. This work underscores the critical balance between wombat survival, burrow utility, and environmental dynamics, offering new insights into mechanisms that dictate mammal behaviour from a thermoregulatory perspective.