Jul 02 2021

Is Climate Change ‘Blocking’ the Progress of Spring?

As we move into summer it’s a good time to look back at our experience of this year’s ‘strange’ Spring weather and assess its effect on woodland wildlife.


In the last few days of March, I can remember taking a few photos of butterflies and beetles, thinking to myself that Spring was warming up nicely. Primroses were blooming and trees were beginning to flower when a feeling of optimism breezed gently through the woods. Two months later, in early June, it is now clear that the seasonal weather we would normally expect didn’t follow the script. The Met Office monthly summary for April said it, “began settled, but soon turned very cold, and a notable feature throughout the month was the number of air frosts. Overall, it was an unusually cold, dry and sunny month.” By the end of the month, I remember having a few conversations with other wildlife survey colleagues who were alarmed by this long period of cold, dry weather and some were even concerned about the fire risk as some areas of Devon heathland had suffered from wildfires.


This Spring, several nests have been built from ‘brown’ material from last year                      A part-built nest from undeveloped leaves. A lot of work for the dormouse without much to show for it.

By coincidence, at Fingle, we were trialling our CCTV nest box cameras on some of the dormouse boxes. In the early Spring we would normally expect to see a few dormice appearing in the boxes, spending a bit of time in torpor and then getting on with building their early season, leafy nests. Sure enough, some dormice did appear on our daily footage. Having left their ground-level hibernation nests, they just curled up in furry bundles and waited out the cold spell … but it went on and on. Using up their winter fat reserves, they appeared to be reluctant to move and were exhausting that vital energy store. The weather wasn’t warming up and the leaves weren’t appearing on the trees. There was very little food and next to no fresh nest building material.


Fingle’s dormice spent a month in the nest boxes in a torpid state with only occasional activity in April
April in England had just 19% of the average rainfall and was the “second coldest April in a series from 1884”. Towards the end of the month, I thought relief was on the way in the form of some rain but, sadly, it wasn’t to be the case. As we moved into May, things were about to get worse. Migrating birds had come all the way from sub-Saharan Africa but arrived in a wintry landscape. The draw of the Dartmoor oak woods, and the plentiful supply of grubs and caterpillars had let them down and now we were in for a long spell of wet weather. Again, the Met Office said that it was “the coldest May since 1996” and the heavy rain and cold winds were causing all sorts of problems around the country. In England it was, “the fifth wettest May in a series from 1862, with 191% of average rainfall, and well over double the average” for much of the Southwest. I can remember being in the woods to do a survey on the 13th of May and an unexpected band of heavy rain sat over eastern Dartmoor for the whole day. This change from cold and dry to torrential rain was all that some of the wildlife could cope with. It was upsetting to find three dead dormice in one week alone as I checked in on a few of them. These poor little creatures had not been able to make nests for warmth and the lack of food had dwindled their winter reserves away. This is the reality of wildlife surveying; it can be cruel sometimes but what is worse is that I suspect that human activity has triggered these climatic changes.
Illustration of an omega block over the UK. Credit: Met Office
Climate researchers are more frequently talking about the Jet Stream these days. This is a ribbon of fast flowing air in the high atmosphere that influences the weather down here at our level. According to a ‘Carbon Brief’ report, “The jet generally keeps a steady stream of weather systems moving across the Earth’s surface. This means that any low-pressure system – or intervening high-pressure system that brings clear, still and sunny conditions – will generally only linger for a matter of days before being shunted on by the next system.” The trouble is these systems are frequently becoming stuck in place for several weeks at a time. The Carbon Brief report explains that “Blocking is a stationary and persistent weather pattern, most often an anticyclone [high-pressure system], that blocks the oncoming jet stream and storms.” So, the variable weather that should roll in off the Atlantic fails to bring the typically changeable weather we like to talk about so much. Climate scientists are now looking at how much of this blocking pattern is down to climate change. It is widely thought that it is happening on an increasingly frequent basis and it certainly fits with what was going on in April and May.
                                    A determined Pied flycatcher pair in a Dartmoor oak wood
Visual clues of a slow Spring have been widespread, from the slow appearance of the leaves on the trees to the late and patchy bluebells that have struggled to bloom. Butterfly surveys have shown a drop in numbers due to the cold but, moving into June I’m feeling a little more optimistic. There is a bit more activity from the dormice; feeding and nesting are both building up, though breeding seems to be about a month behind. I have also been keeping an eye on a brave pair of pied flycatchers that have managed to delay nesting and may have time to raise a brood. Some may have missed their nesting opportunity this year, but the adult birds will hang on for now. Dormice may be lucky and could have a successful late season litter but the real effects on the wildlife may not be seen until next year.
The major issues of climate change and ecological survival are not two separate concerns, they are two components of the same system that keeps us all alive on this wonderful planet. If this weather pattern happens once it can cause problems but, in consecutive years, the loss of adults of breeding age and repeated failures to raise a brood or a litter could have detrimental effects on the population. As we look forward to a summer of more freedom for us humans, we must not forget the wild species and how their plight may not be that far away from getting critical for all of us. We need to keep a close eye on nature as the woodland wildlife barometer has something important to show us.by Matt Parkins

… with a little help from Carbon Brief and their report:
Jet stream: Is climate change causing more ‘blocking’ weather events? | Carbon Brief

from https://finglewoods.org.uk/
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