This diagram helps compare the occurrence of phenological spring stages. "Bloom" means first few fully open flowers, not that the plant was in full bloom already. There is no general rule, development depends on the species and the circumstances: E. g. the golden saxifrage was earlier than last year because it could handle the second cold spell easier than others. The white butterbur originally was earlier but was hindered, some plants even damaged by the cold spells. The cowslip would have been earlier than 2017 but was stopped by the second cold spell. The windflower was ready and could await the end of the cold spell without damage and finally opened around the same doy as 2017. The birds seem to behave differently: resident birds as the blackbird rather depend on regional factors as day length (and less on temperature as it seems) whereas migratory birds rather depend on supraregional factors which trigger migration. The song thrush is a partial migrant in my region.
