No abstract

a b s t r a c tCommon hamsters (Cricetus cricetus) are hibernators and therefore show a pronounced seasonal breeding behaviour. Previous studies suggest that an early onset of reproduction after vernal emergence can be crucial for reproductive success in the current year. In Vienna, the winter 2005/06 was exceptionally cold and snow cover lasted until late March. This enabled us to investigate the effects of harsh winter conditions on seasonal timing and reproductive success in female Common hamsters. We investigated differences in the timing of the active season, reproductive performance and physical condition before hibernation between 2006 and previous years (2003-05) to determine potential environmental effects. Hamsters were live-trapped throughout the active period, weighed, individually marked and reproductive status was determined. The number of litters per season and litter size were determined in individual females. Vernal emergence in 2006 was considerably delayed and females mated significantly later than in 2003-05. Reproductive output in 2006 was about half that of the preceding years. This was particularly pronounced in the size of the females' first litters per season. The number of litters per female was similar in all periods. Almost 90% of the females in 2006 mated shortly after parturition and overlapped lactation of the first and gestation of the second litter. In 2003-05, only about one-third of the focal females successfully produced a litter after a postpartum oestrus. The time delay in spring 2006 led to a shorter active season compared to previous years reflecting the time constraints in this species. In conclusion, the results demonstrate that environmental factors can affect seasonal timing, reproductive output and preparation for hibernation in female Common hamsters.