Abstract:
Shifting activity to cooler times of day buffers animals from increased heat and aridity
under climate change. Conversely, when resources are limited, some nocturnal species
become more diurnal, reducing energetic costs of keeping warm at night. Aardvarks
(Orycteropus afer) are nocturnal, obligate ant- and termite-eating mammals which may
be threatened directly by increasing heat and aridity, or indirectly by the effects of
climate change on their prey.We hypothesised that the minimum 24-h body temperature
of aardvarks would decline during energy scarcity, and that aardvarks would extend
their active phases to compensate for reduced resource availability, possibly resulting
in increased diurnal activity when aardvarks were energetically compromised. To
measure their thermoregulatory patterns and foraging activity, we implanted abdominal
temperature and activity data loggers into 12 adult aardvarks and observed them for
varying durations over 3 years in the Kalahari. Under non-drought conditions, aardvarks
tightly controlled their 24-h body temperature rhythm (mean amplitude of the 24-h body
temperature rhythm was 1.8 0.3 C during summer and 2.1 0.1 C during winter)
and usually were nocturnal. During a summer drought, aardvarks relaxed the precision
of body temperature regulation (mean 24-h amplitude 2.3 0.4 C) and those that
subsequently died shifted their activity to progressively earlier times of day in the weeks
before their deaths. Throughout the subsequent winter, the aardvarks’ minimum 24-h
body temperatures declined, causing exaggerated heterothermy (4.7 1.3 C; absolute
range 24.7 to 38.8 C), with one individual’s body temperature varying by 11.7 C within
8 h. When body temperatures were low, aardvarks often emerged from burrows during
daytime, and occasionally returned before sunset, resulting in completely diurnal activity.
Aardvarks also shortened their active periods by 25% during food scarcity, likely to avoid energetic costs incurred by foraging. Despite their physiological and behavioural flexibility, aardvarks were unable to compensate for reduced food availability. Seven
study aardvarks and several others died, presumably from starvation. Our results do
not bode well for aardvarks facing climate change, and for the many animal species
dependent on aardvark burrows for refuge.
