Abstract:
Climate change threatens biodiversity by compromising the ability to balance energy
and water, influencing animal behaviour, species interactions, distribution and ultimately survival. Predicting climate change effects on thermal physiology is complicated
by interspecific variation in thermal tolerance limits, thermoregulatory behaviour and
heterogenous thermal landscapes. We develop an approach for assessing thermal vulnerability for endotherms by incorporating behaviour and microsite data into a biophysical model. We parameterised the model using species-specific functional traits
and published behavioural data on hotter (maximum daily temperature, Tmax > 35°C)
and cooler days (Tmax < 35°C). Incorporating continuous time-activity focal observations of behaviour into the biophysical approach reveals that the three insectivorous
birds modelled here are at greater risk of lethal hyperthermia than dehydration under
climate change, contrary to previous thermal risk assessments. Southern yellow-billed
hornbills Tockus leucomelas, southern pied babblers Turdoides bicolor and southern
fiscals Lanius collaris are predicted to experience a risk of lethal hyperthermia on ~
24, 65 and 40 more days year−1
, respectively, in 2100 relative to current conditions.
Maintaining water balance may also become increasingly challenging. Babblers are
predicted to experience a 57% increase (to ~186 days year−1
) in exposure to conditions associated with net negative 24 h water balance in the absence of drinking, with
~ 86 of those days associated with a risk of lethal dehydration. Hornbills and fiscals
are predicted to experience ~ 84 and 100 days year−1
, respectively, associated with net
negative 24 h water balance, with ≤ 20 of those days associated with a risk of lethal
dehydration. Integrating continuous time-activity focal data is vital to understand and
predict thermal challenges animals likely experience. We provide a comprehensive thermal risk assessment and emphasise the importance of thermoregulatory and drinking behaviour for endotherm persistence
in coming decades.
