Effect of photoperiod and ambient temperature on activity patterns and body weight cycles of mountain pygmy‐possums, Burramys parvus (Marsupialia)

Abstract

The mountain pygmy‐possum Burramys parvus shows strong seasonal rhythms of reproduction and activity in summer, pre‐hibernation fattening in autumn and hibernation in winter. We investigated whether photoperiod or air temperature (Ta) or interactions of these environmental factors influence activity patterns, fattening and onset of hibernation. In January 1993, 10 Burramys held under long photoperiod were divided into two groups. One group was maintained under the previous long photoperiod (LD 14.5:9.5; n= 5), the other was transferred to short photoperiod (LD 9.5:14.5; n= 5). The Ta was reduced in steps lasting at least one month from 12 to 8 to 4 and to 2°C. All individuals showed pronounced daily activity rhythms and were mainly nocturnal. Individuals under short photoperiod maintained their nocturnal activity pattern irrespective of Ta. In contrast, most individuals under long photoperiod at Ta 4 and 2°C temporarily showed a free‐running activity rhythm and began their activity period during the day. Body weight and total daily activity were negatively correlated. Individuals with low body weight (<50g) generally were more active and showed longer activity periods than heavy animals. Under both photoperiods these lean individuals often extended their activity periods into the light phase. While in the first year after capture all animals showed pre‐hibernation fattening and hibernation, a second body mass cycle was observed in only five individuals and this was independent of Ta and photoperiod. However, total daily activity in these individuals decreased with increasing body weight. Our study shows that photoperiod has little influence on seasonal changes of activity, body weight and hibernation of Burramys. Low Ta has some effect on activity patterns of Burramys held under long photoperiod. Body weight and activity of Burramys were interrelated suggesting that pre‐hibernation fattening occurs during a time of reduced activity and thus low energy expenditure.