Heat stress in flying-fox camps

Over the past two decades, several documented heat stress events have caused significant numbers of flying-fox deaths.

During the day, flying-foxes roost in patches of trees, known as camps, which may contain tens to thousands of individuals. As a result, they can be susceptible to extreme weather conditions.

Heat stress - or hyperthermia - occurs when the body produces more heat than it can dissipate. Flying-foxes are generally affected when temperatures exceed 42°C and roost vegetation in their camps doesn't provide enough shade refuge. Post-mortems suggest that flying-foxes mainly die from resulting heat shock i.e. the body can no longer function effectively.

The severity of a heat stress event is likely to be reduced by:

  • enough understorey and mid-storey vegetation for shelter from extreme heat
  • dense crown vegetation to provide shade
  • access to enough water.

Severity is likely to be increased when camps are disturbed at critical times during a heat stress event, potentially forcing individuals to leave their cooler microhabitats and become fully exposed to the extreme heat.

Normal roosting in a flying-fox camp
Flying-foxes cluster together and move towards the ground during a heat stress event.

When ambient temperatures rise above 35°C, flying-foxes express certain thermoregulatory behaviours to reduce their internal body temperature. These include:

  • licking wrists and wing membranes
  • wing-fanning
  • panting
  • shade-seeking, which may result in clustering
  • descending to lower levels of vegetation
  • descending to ground level.

The impacts of heat stress events are likely to vary site to site and can depend on conditions in the preceding days. Ambient temperature alone may therefore not be a sound indicator of a heat stress event and thermoregulatory behaviours in flying-foxes may be a more reliable indicator of whether they are affected.

Note: As flying-foxes can lick and wing-fan for other reasons, these behaviours alone should not be used to identify if they are heat stressed.

Never touch a flying-fox. If you see flying-foxes panting or climbing down roost tree towards the ground, call a licensed wildlife rescue and rehabilitation provider or use the IFAW Wildlife Rescue App to quickly find the closest licensed carer. They can assess the situation and help the animals as needed.

Leave it to the experts. Helping heat-affected flying-foxes requires experienced and licensed wildlife carers to assess and implement appropriate interventions and to avoid additional harm to the animals.

In many cases, flying-foxes may be able to cope with the heat on their own. In these situations, it's best not to approach them as this may be disturbed and take flight, potentially weakening them further.

If flying-foxes have died during a heat stress event, don't let domestic dogs and cats into the camp.

Preliminary research shows the likelihood of cats and dogs becoming infected following contact with a bat infected with Australian bat lyssavirus is low. However, it is theoretically possible that a pet that has come into contact with an infected bat could contract the virus and could then transmit that infection to a human.