Do the abiotic environmental factors influence the reproduction rate in the free-ranging European bison in Bialowieza Primeval Forest?

Abiotic factors such as sunspot activity, radiation, insolation, air temperature and rainfall in the Białowieża Primeval Forest were measured for 26 years and the number of mature cows and bulls, calves born each year, bull/cow and calPcow ratios were counted. Results showed that, in 26 years, 984 calves were born (482 males and 502 females). The sex ratio was 0.96. The number of calves depended mostly on the bull/cow relation which changed from 0,12 to 0.46. Calf/cow ratio changed from 0.32 to 0.92. The rainfall in September was the most important abiotic factor. Less rain was associated with more male calves and an alteration in the male/female ratio in next year. The same concerns the calf/cow ratio. Rainfall over 3 mm in September diminished this ratio to 0.6. The other abiotic factors did not influence the fertilisation in the bison cows in the 3 autumn months. However, they showed the range of environmental indices, to which all animals living in the Forest must adapt their metabolism.