Researchers using thermal imaging to study numbats in Western Australia have found the animals are limited as little as 10 minutes of activity in direct sun before overheating during hot weather.
The findings have important implications for the conservation of this endangered species, as numbats reintroduced into hot arid environments will be most potentially vulnerable to the impacts of global warming.
Numbats (Myrmecobius fasciatus) are the only truly diurnal marsupial, meaning they are active only during the day.
“With an exclusive diet of termites, numbats are often exposed to high temperatures and gain heat from direct sunlight. Even when in the shade they gain heat from radiation from the ground, rocks and trees,” says lead author Dr Christine Cooper from Curtin University, who championed the numbat in 2022’s Australian Mammal of the Year Competition.
“We found when it is cold, numbats keep warm by raising their fur to provide better insulation and to allow more radiation to penetrate. When it is hot, they depress their fur to facilitate heat loss and shield the skin from solar radiation. In this way their body functions as a thermal window that allows heat exchange.
Numbats were once found across southern Australia but only two remaining natural populations persist today, both in wheatbelt reserves in WA. One population is found at Perup Nature Reserve and the other at Dryandra Woodland, where the study was done.
They are known for their distinctive stripes, Cooper says they do not have a role in heat balance, rather their most likely function is for camouflage.
Infrared thermal videos of 50 wild numbats recorded over 2020-2021 revealed that the animals are prone to overheating, when body temperatures exceed 40°C, in just 10 minutes when foraging at wet bulb globe temperatures (WBGT) exceeding 23°C.
Credit: Christine Cooper
WBGT is a measure of heat stress in direct sunlight, which considers temperature, humidity, wind speed, sun angle, and cloud cover.
“With an estimated population of only about 2000, numbats are under threat from habitat loss and introduced predators like foxes and feral cats,” says Cooper.
Several populations of numbats have already been successfully re-introduced into parts of their historical range, but the findings of this study highlight shade availability as a critical resource for numbat habitats and suggest that future translocations to hotter inland arid zones must be carefully considered.
“In terms of habitat requirements, our findings show the importance of considering temperature and shade availability when planning translocations for the conservation of this endangered species, particularly given our warming climate,” says Cooper.
This is because global warming not only impacts average ambient temperature and average annual rainfall, but also increases the frequency, intensity, and duration of heatwaves.
Credit: Christine Cooper
“Even with shade available, higher temperatures will reduce how long numbats can forage during the day, and because they have limited capacity to become more nocturnal, heat may become problematic for numbats,” she adds.
“Understanding how the numbat responds to and manages heat is essential to understanding its ecology and has particular relevance for the future conservation and management of the species in the face of global warming.”
The research has been published in the Journal of Experimental Biology.
