Annual variations in the population growth rates were significantly related to autumn climate and winter climate between year t and t + 1. High growth rates were found in years with mild weather during the period September–November (b = 0•039, P = 0•001) and with little snow depth in May (b = −0•005, P = 0•008). The proportion of explained variance in σe2 was 9•7% and 1•1% for autumn temperature and May snow depth, respectively.