Phenology - A Comparative Countryside Calendar

Notes on Comparisons and Changing Times

by Roger Tabor

When we are looking at the effect of changing seasons on wildlife over a long period, it is important that we are comparing like with like. To make a proper comparison on historic records it is important to allow for the change in the calendar made in 1752. Up until then Britain had followed the Julian Calendar which had been in existence since the early years of Christianity in the Roman Empire. Pope Gregory XIII had implemented the Gregorian Calendar 170 years earlier for the Catholic Church and it had been adopted across most of Europe. When Britain took on the new Calendar there was a slippage of 11 days. Consequently some of our old weather 'love' is slightly out of synchrony.

For example, by traditions birds are said to choose their mates and fall in love on 14 February, St. Valentine's Day. On the old calendar that was where 25 February is today, and yes Blackbirds and some other residents start to sing, form pairs, and look for nest sites. However, 14th February can be a bit bleak for much ardour!

May Day, the 1st May, was on the old calendar when May or Hawthorn blossomed (on the earlier of the two British species). However, that event was shifted on to around the 12th May.

But, remember that is overlaid on the import detail of where you are. The warming of Britain with the changing seasons starts each year in the farthest south of Britain (the S.W. peninsular) and moves north up the country.

During the winter plants are resting, and only resume active growth when the daily mean temperature goes up past 6ºC. Only then can early Spring 'kick off'. For an average year over the 20th century in the extreme S.W. points of Cornwall and Ireland, that temperature was reached by 14th February. By March 1st most of Cornwall and South Devon and South Dorset, and the western counties of Ireland had reached it. By mid-March most of Eire was blessed with the growing warmth, as were South Kent, South London across to Bristol and the peripheral counties of Wales. By the 1st April only the high-ground of North England and Scotland had yet to reach this magical seasonal mark. Global warming will affect the position of these seasonal zones.

On top of this, is that large urban areas act as huge "storage radiators" for heat. In consequence London has very few frost nights compared to a similar latitude in adjacent Essex, and its Spring season also begins earlier.

© Roger Tabor 2000