Seasonal Update (January 2021)

A hoar frost on the New Forest. The New Year got off to a chilly start across the UK, with dawn temperatures well below freezing. - Credit: Marc Baldwin

November was a broadly mild month across the country, with temperatures several degrees above average for the time of year. The final week saw cooler weather across much of the UK, bar the far south and south-east which was still in the grip of mild continental air. Another mild front arrived to kick off December, with temperatures of 11C (52F) in Stornoway, Scotland, but this lasted for only a day before a north-westerly airflow dropped temperatures. Indeed, overall, despite this cold first week, December was another very warm and wet month; the month’s average (across the whole UK) sitting at +1.2C (+2.2F) by Christmas Eve, but much milder in the south.

The first snow of the season arrived early, towards the end of the first week, with south Wales and the southwest of England seeing flurries, while Scotland and eastern England, even as far south as Kent, saw accumulations of several centimetres. The Scottish Highlands saw more than 10cm (4 in.) of snow in places as temperatures dropped well below 0C (32F). Parts of the northwest awoke to “thundersnow” on the morning of the 4th December. The snow was short-lived and rapidly turned back to heavy rain and strong winds, which lasted into the first weekend.

The second week started on a very cold and foggy note widely across the UK – temperatures struggled to reach 4C (39F) even here on the south coast after starting the day at -2C (28F). On the Tuesday, however, low pressure moved in from the North Sea bringing heavy rain and gusty winds to Scotland. This system worked its way across the country in a couple of days and Stornoway was basking in 9C (48F), while here in the south we had an unseasonably mild 12C. Much of Europe was also well above average for the time of year.

After a cold and settled Christmas Day, Storm Bella brought rain and very strong winds to most of the UK. - Credit: Sue Cro (CC BY-NC 2.0)

Week three picked up where week two left off, feeling much less seasonal, with temperatures remaining around 9C in the Scotland and 13C (55F) here in the south; even Bedfordshire in the Home Counties was at 12C (54F) by the end of the week. Typically, by this stage in December, we'd expect daytime highs of around 5C (41F) in Scotland and 8C (46F) in the south, so the third week was very mild. With the warm air mass came wet and windy weather, with gales through the Irish Sea and English Channel in the second half of the week. Amber warnings for rain were issued for south-west Wales.

Christmas week began in the same vein – mild, wet and windy – although there was a distinct contrast across the country. Temperatures in the southeast hit 15C (59F) on the winter solstice and on the following night we saw “lows” of 11C in the south-west, while northern England and Scotland hovered around freezing. The middle of the week brought a large area of low pressure to much of southern and midland England, dumping up to 70mm (2.8 in.) of rain on already saturated ground and prompting the Met Office to issue a yellow warning for flooding. This disruption from the rain continued over the festive period for some as just over 1,000 people had to be evacuated from the Billing Aquadrome holiday park in Northamptonshire on Christmas Eve night as floodwaters rose to 1.5m (5 ft.).

Most of the country did, however, get a brief window of festive weather over Christmas, with a transient ridge of high pressure bringing a northerly airflow and dropping temperatures down to just below the seasonal average for much of Christmas Eve and Christmas day – almost like Mother Nature was trying to cheer us up. Indeed, in a highly unusual weather event, parts of the northern and eastern UK (e.g. Aberdeen, parts of Yorkshire including Durham and Huggate and East Anglia) saw snow on Christmas Eve and a light dusting on Christmas Day, making 2020 the first white Christmas for a decade.

While many of us yearn for the Christmas card scenes of Victorian England at this time of year, snow on Christmas Day remains a rare event. Christmas falls early in winter and the kind of temperatures we need for snow typically don't manifest until midwinter. Hence, January or February tend to offer the best prospect of some of the white stuff. Of the last 60 years, only five had snow fall on Christmas Day: 1981, 1995, 2009, 2010 and this year. Worse, for those of us wanting to follow Noddy Holder’s instruction of riding off down a hillside, the projected climate warming suggests that snow could be a thing of the past in almost all but the highest parts of the UK by 2060.

Unusually for Britain, many areas saw snow over the festive period, making 2020 the fifth white Christmas in 60 years. - Credit: Randi Hausken (CC BY-SA 2.0)

Mild and wet conditions returned on Boxing Day with severe gales (106mph recorded at The Needles on the Isle of Wight) for most of England, courtesy of the large midlatitude storm named “Bella” by the Met Office. Bella had a circulation field of up to 4,000km (almost 2,500 miles), making its total area larger than the area of Europe. Once Bella passed, temperatures fell to just below average and, more generally, they were above average to end December for eastern Europe, and at or slightly below for western Europe. Along the south coast, December ended on a cold, grey and wet/sleety note, while further north saw some welcome (and not-so-welcome) snow.

Perhaps of more interest to those wanting something more seasonal this winter, was the observation that on Christmas Eve it was -16C (3.2F) at the North Pole, with a wind chill of -30C (-22F) and most models predicting an extensive blocking (at 1,050 mbar) around Greenland for at least the first week in January, pushing the jet stream unusually far south (down towards Morocco). This barometric pattern locks in what meteorologists refer to as a “northern blocking” for the UK. Basically, this means northerly and north easterly airflows, bringing cold air to kick off the new year. Certainly, on the 23rd December we saw the start of pronounced stratospheric warming over Siberia, which started to displace the polar vortex out into North America and North Atlantic, in line with the predictions and some very cold weather saw out 2020 and in 2021. It was -2.6C (27F) at dawn on New Year's Day even right down here on the south coast of England. 

This Christmas was vastly different to most of us owing to the restrictions on household mixing over the festive period having been cut to only Christmas Day itself. Nonetheless, I hope it was as good as it can have been for you and your family, and wish you a very happy and healthy 2021.

If you’re interested in the wildlife to be found this month, including a look at bank vole behaviour, the peak of the fox breeding season, and the start of the pair-bonding season for tawny owls, check out my Wildlife Watching - January page.

Website news

I’ve been mostly focusing on the water deer research recently, so new content has been very limited. Nonetheless, some minor updates have been made to the squirrel section and a new SpeedRead has been added covering the Edible dormouse.

In the news

A few of the science and conservation news stories that caught my attention while digesting Christmas dinner and arguing with myself whether I could justify both a slice of cake and a mince pie include ambidextrous squirrels being superior learners, how spiders use electricity to “fly”, and how ravens are even smarter than we thought.

A Red squirrel (_Sciurus vulgaris_) kitten feeding. Squirrels show a tendency for right- or left-handedness, but new research suggests they may be slower learners than ambidextrous individuals. - Credit: Marc Baldwin
  • Handed hindrance? We know that most humans and a few other animals prefer to use one hand or paw over another, and scientists call this ‘handed preference’ being “strongly lateralised”. Back in 2015, a team of Spanish biologists demonstrated right- and left-handed preferences in Red squirrels (Sciurus vulgaris), but new research by Lisa Leaver and her colleagues at the University of Exeter found Grey squirrels (Sciurus carolinensis) that showed a preference for using either paw over the other learned cognitive tests more slowly than those without strong lateralisation.
  • Going batty for AI. Monitoring the populations, movements and behaviours of small nocturnal animals is always a challenge, and when you add flight and woodland habitat to the equation, the problem is almost impossible. In a bid to make monitoring of bats a little easier, a joint team of Forestry Commission and Bat Trust scientists set up a low-cost static acoustic sensor at 60 locations across 16 forests in eastern England over 36 nights. The 400 surveys recorded 7 million potential bat calls that would normally have to be sorted through. A new AI tool, called AudioMoth, developed by researchers at the University College London came to their rescue. After sorting through all the recordings, the software identified 1.7 million bat calls allocated to eight species.
  • Airborne arachnids. Despite their lack of wings, spiders are able to take to the air allowing the colonisation of new habitats. They climb to an exposed point, point their abdomens skyward and exude a string of silk, which appears to catch the wind and allow them to float away, a process we call “ballooning”. Until recently (and, yes, I know this is old, and I’m well behind the curve on this, but I only came across this over Christmas) we didn’t really understand how this ballooning worked, particularly as spiders only do it during gentle breezes that don’t seem to have the power to carry them. Research by the University of Bristol has now shed some light on this most curious of behaviours and it turns out that they actually take advantage of electric potentials. Silk leaving their abdomen typically picks up a negative charge and is repelled by the negative charge of the plants they’re standing on. Plants, being rooted in the ground, are quite literally earthed, and yet they protrude into the positively charged air, setting up significant electric fields between the air and the tips of their leaves and branches. Erica Morley and Daniel Robert found that this repellent was sufficient to lift adult Erigone into the air.
  • Cogent corvids. If you were asked to list some of the most intelligent animals, it’s a fairly safe bet that corvids would feature high up on the chart. In the rankings of smartest members of the bird family, ravens arguably sit at the top, displaying complex social, political and problem-solving behaviour. Now, it seems that they’re smart even at a young age. By presenting hand-reared ravens a series of puzzles at four, eight, 12 and 16 months old, Simone Pika and her team at the Max Planck Institute for Ornithology in Germany found that cognitive performance develops very rapidly and is pretty much complete by the time the bird is four months old. Moreover, when compared with 106 adult chimps and 32 adult orangutans that completed similar tasks, the four-month-old ravens were similar in their mental prowess, suggesting their cognitive performance may parallel some adult higher apes.

Discoveries of the Month

Chinese puzzle: new insights on the conservation importance of Britain’s water deer population

Britain is home to an impressive seven species of deer, although only two – the Red deer (Cervus elaphus) and Roe deer (Capreolus capreolus) – are considered native, the others having been introduced from Europe and Asia. Among this cervid menagerie is a diminutive species native to the wetlands and hill farms of China and Korea, the Chinese water deer (Hydropotes inermis). Probably the least known of our wild deer species, water deer exhibit a strange trait whereby males do not grow antlers – instead, they have hypertrophied canine teeth that are used during dominance displays and in combat.

A Chinese water deer (_Hydropotes inermis_) doe in wheat field. This species was introduced from China in the late 1800s and several escapes and deliberate releases has resulted in it becoming established in large sections of the Home Counties, with a stronghold in East Anglia. - Credit: Marc Baldwin

Water deer are small cervids found primarily in eastern England. First described in 1870 and introduced several times to the deer park at Woburn Abbey by the 11th Duke of Bedfordshire, from which some escaped and some were deliberately released, they have now spread across a reasonably wide area of central and south eastern England, particularly the farmland of Bedfordshire and Buckinghamshire and the reedbeds of Cambridgeshire and Norfolk. Despite spreading more slowly than other introduced deer, the English population is currently thought to stand at 8,000-10,000 animals. Following drastic declines in China, owing to a combination of habitat loss and poaching, the apparent prospering of this species over here means that Britain may hold as much as 30% of the world’s water deer. Now, genetic data suggest the population may be even more important than we first thought.

A team of scientists, led by Vincent Savolainen at Imperial College London, recently subjected water deer tissue samples collected by Richard Fautley as part of his Ph.D. thesis to more detailed genetic analysis – amplifying and sequencing the non-coding control region and the coding cytochrome b gene (Cytb). Samples were collected from Cambridgeshire, Norfolk, Bedfordshire, France, China and an unspecified location in South Korea. The results of the analysis are currently in press with the Zoological Journal of the Linnean Society.

The analysis revealed that the genetic diversity was substantially higher in the Chinese samples than in those from either the UK or France, suggesting both that the population in China has undergone a recent sharp decline and that the British population probably stems from the introduction of only a few individuals of Chinese origin. Indeed, the most prevalent Cytb haplotype in the Whipsnade population was also found in samples from across China, Britain and France, suggesting an expansion from a single source and consistent with historical records suggesting animals were introduced to Whipsnade from Woburn and both escaped from Woburn and were translocated from there to Woodwalton Fen in Cambridgeshire.

A Chinese water deer (_Hydropotes inermis_) buck. This species is unique among Britain's deer in that the males do not possess antlers, instead growing long canine teeth (up to 8cm/3 in.) that they use in combat. - Credit: Marc Baldwin

Perhaps of more importance was the observation that the British water deer samples grouped independently in their network analysis. Writing in the journal, the researchers explain:

Our results suggest that the Chinese water deer residing in the UK may be the descendants of a now extinct Chinese mainland population – a reservoir of genetic variation that has been lost in the native range.”

They go on to suggest that this finding should prompt conservationists to consider the inclusion of individuals from British stocks to help augment the genetic diversity of reintroductions in China.

Source: Putman, R. et al. (2021). Conservation genetics of native and European-introduced Chinese water deer (Hydropotes inermis). Zool. J. Linn. Soc. zlaa076. doi: 10.1093/zoolinnean/zlaa076

Gimme shelter. Cover significantly influences survival of Brown hare leverets

Despite being a non-native species, introduced to the UK at some point during the Iron Age, the Brown hare (Lepus europaeus) is a familiar and largely welcome sight in Britain’s countryside. They’re currently widely distributed across Eurasia, from Cornwall in the west to western Mongolia in the east, north into Finland and south to Jordan. They have also been introduced quite widely, including to South America, Australia and New Zealand.

Here in the UK, the species is doing reasonably well, although, akin to the Chinese water deer discussed above, the same cannot be said throughout much of its native range, with population declines recorded across Europe since the 1960s. Indeed, Norway, Germany, Austria and Switzerland are among the countries to have added the Brown hare to their Red List as either Endangered or Nearly Threatened, while Spain has recently embarked on a captive breeding programme. Consequently, several studies have been undertaken recently to better understand what factors affect hare survival to identify what can be done to help reverse the decline.

A Brown hare on a farm in Buckinghamshire. While doing reasonably well in Britain, hare populations are decline in several European countries. - Credit: Stephanie Powley

One such study was conducted by Ulrich Voigt and Ursula Siebert at the University of Veterinary Medicine Hannover Foundation’s Institute for Terrestrial and Aquatic Wildlife Research. Between 2004 and 2010, Voigt and Siebert monitored the hare population in the undulating Hildesheimer Boerde agricultural landscape of northern Germany, observing, tagging and radio-tracking 229 leverets to assess their survival. The researchers recorded the death of 60 leverets (26%) over the course of the study, although the fate of a further 105 could not be determined. Losses to predators (foxes, martens, domestic cats, crows, buzzards and owls) accounted for 42% of the known mortality, while 12% died from unknown causes and 10% from disease, hypothermia or contact with pesticides.

Previous studies have shown that the abundance and fluctuations in European hare populations are primarily the result of changes in the survival rates of leverets, rather than the mortality among adults. This was apparent in this research, which calculated that only 33% of leverets survived through weaning. The data show that the most common factor associated with mortality was the choice the leverets made for their hiding spot. Brown hare leverets are born into a nursery form, essentially a scrape or furrow in the ground made by the mother, and at between two and four days old they move away to find their own hiding places to lay low waiting for their mum to return to feed them. Writing in the European Journal of Wildlife Research, the scientists explain that leverets opting for more exposed resting locations were more vulnerable:

“… the daytime user ‘open’ animals die more frequently and faster than the ‘concealed’ ones or those animals which were born without cover but moved to the next adjacent shelter, therefore having a better chance to survive.”

The authors conclude that the application of set aside areas would help increase survival by providing more opportunities for cover at the periphery of fields and ditches, where leverets tended to choose as daytime resting spots.

Source: Voigt, U. & Siebert, U. (2020). Survival rates on pre-weaning European hares (Lepus europaeus) in an intensively used agricultural area. Eur. J. Wildl. Res. 66:67. doi: 10.1007/s10344-020-01403-z.

Related reading