Seasonal variations in climate happen in all habitats, with the most extreme seasonal changes generally occurring in temperate or Arctic regions. Seasonal changes in ambient temperature, rainfall patterns and other weather variables can result in different primary productivity and consequently different physiological demands on animals. Further, photoperiod also changes seasonally, and this is particularly pronounced at high latitudes. For animals such as bats that hibernate all winter, it is especially vital for them to obtain enough food throughout the summer to have enough fat reserves for the hibernation period. However, bats typically forage at night, therefore, it could be difficult for bats that live at high latitudes to obtain enough energy reserves throughout the short nocturnal periods of summer.
We have researched how small mammals respond to seasonal changes in tropical, subtropical and temperate regions. In particular, our research has focused on how metabolism and thermal physiology change throughout the year. For example, many mammals employ torpor, a reduction in body temperature and metabolic rate, in order to conserve energy. Some mammals employ torpor seasonally and hibernate throughout the winter months, whereas others use torpor opportunistically whenever environmental conditions are detrimental.
The graph below provides an example of how skin temperature patterns of a small insectivorous bat (Nytcophilus bifax) varies between summer and winter. During the warmer summer months bats generally have abundant food sources and spend the nights active and hunting, but typically lower their body temperature during the day to save energy. In contrast, throughout winter bats need to spend a lot of energy to maintain a high body temperature due to the cold conditions, and with a greatly reduced food supply they opt to hibernate and mostly keep a low skin temperature.
Figure taken from: Stawski C, Geiser F (2010) Seasonality of torpor patterns and physiological variables of a free-ranging subtropical bat. Journal of Experimental Biology 213:393-399, doi:10.1242/jeb.038224.
Downloading data for this research at Iluka Nature Reserve, a coastal subtropical forest in NSW, Australia. Copyright: Margaret Stawski