Cold snap

Here are some numbers to go with this week’s cold snap.

 Zero: a frost day is any day in which the minimum temperature falls below 0°C.

Forty four: in 2022 there were 44 frost days recorded in the UK.

Four: 4°C is this decade’s average January temperature in the UK. This number is rising slowly, a reflection of our warming planet.

Five: 5°C is the temperature at which grass stops growing.

Eight: we are in Zone 8 of the frost map published by Plantmaps, which predicts that the reserve’s last frost will occur in the final ten days of March.

Twenty: in order to stretch resources as far as possible during the winter, a common shrew shrinks by up to 20%; its spine shortens, cartilage is re-absorbed and even the brain and skull get smaller. Moles use the same tactic, shrinking by 11%.

Five hundred: the weight in grams that a hedgehog must achieve if it is to survive hibernation. Late-born hoglets don’t usually make it through their first winter without help.

Seventy: the percentage increase (70%) in the weight of a house sparrow’s plumage as it prepares for winter. Most of the additional weight comes from a dense layer of down close to the bird’s skin.

Six: the percentage of its body weight a great tit can lose overnight in cold weather. Small birds need shelter in a cold snap so leave your bird boxes out for the winter, cleaned and with a handful of dried grass or dead leaves in the bottom.

Eighty: approximately 80% of blue tits die in their first winter.

Go carefully in this treacherous weather.