Abstract:
Multimammate mice are prolific breeders, can cause significant agricultural damage, and are reservoir hosts for a
number of pathogens. They are nocturnal and given their success in urbanised rural environments, we were
interested in how they would respond to increasingly bright anthropogenic spaces. We evaluated the locomotor
activity of southern multimammate mice (Mastomys coucha), under four treatments: in an outdoor enclosure with
natural light and temperature fluctuations, in a laboratory under a standard light regime, and two artificial light
at night (ALAN) regimes (2 Lux) of varying proximity. The study animals remained nocturnal for the duration of
the experiments. They were more active under the laboratory conditions with lower day-time light levels
compared to the outdoor treatment but reduced their activity under ALAN. When the night light originated
remotely, activity levels decreased by more than 50%, whereas under direct ALAN from above the cages, there
was a 75% decrease in activity. The onset of activity was later during the two LAN treatments. We concluded that
Mastomys coucha is strongly averse to light and show severe behavioural and circadian responses to light at night.
We predict that it is unlikely that Mastomys will flourish in cities, but that they could thrive in and around dark
urbanised refugia.
