Seasonal Update (December 2023)

December marks the start of winter but, despite what Christmas cards portray, it's seldom cold enough for snow and frosts can be few and far between. - Credit: Marc Baldwin

Welcome to winter. As the twelfth and final month of the Julian and Gregorian calendars, December (together with January) was called Ġēolamōnaþ or Ȝēolamōnaþ by the Anglo Saxons, meaning “Yule month”. The name December has its roots in the Latin decem, meaning “ten”, because in the 750 BP calendar of Romulus, which started in March, it was the tenth month of the year. It's the month containing the winter solstice here in the northern hemisphere; the north pole is tilted its furthest from the sun, bestowing upon us the shortest period of daylight in the year. In the southern hemisphere, the solstice represents mid-summer, and makes Father Christmas wish he'd selected more appropriate attire for his seasonal outing. With that in mind, I would like to take the opportunity to wish all my readers and their families a wonderful Christmas and/or festive season, whatever you do or don't celebrate, and to thank you for your interest over the past year.

Weather update

November kicked off on a stormy note as storm “Ciarán” brought rain and 70 mph (113 kph) winds to the south coast in the first week. The storm tracked further south than originally forecast meaning that the Channel Islands caught the brunt of it, suffering widespread damage, with 102 mph (164 kph) wind gusts and golf ball-sized hail stones. This storm followed a week of heavy and persistent rain that had already caused widespread flooding across much of the UK and Ireland to see out October.

Despite ending November and starting December with some very cold weather, much of Europe also experienced above average temperatures last month. - Credit: WX Charts (CC BY-NC-ND 2.0)

The second week was one of sunny spells and showers across the UK, punctuated by a large low pressure passing through on Wednesday and bringing yet more wind and rain to most places. Temperatures remained around average at 9C to 13C (48-55F) north to south, with some very chilly nights that brought the first frosts of the autumn, even close to the coasts. The low-dominated airflow throughout November brought a succession of low-pressure systems with wind and rain, and temperatures, overall, above average. As storm “Debi” moved across at the start of week three we saw 80 mph winds across northern England and Northern Ireland and temperatures of 16.2C in west London and 16.6C (61.9F) in Merryfield, some 5C (9F) warmer than we'd expect for this time of year.

The second half of November was an unsettled affair with several areas of low pressure moving across the country and plenty more heavy rain, exacerbating the flooding many parts were already suffering from October and early November. Temperatures fluctuated but tended to remain slightly above the seasonal average, particularly overnight, before a deep cold pulse to end the month, with temperatures struggling above freezing for most of the country for the last week. This early cold snap didn't last long, and we were back to mild, wet and windy come the end of the first weekend of December.

Outside of the UK, parts of western Europe were also hit by Ciarán, with winds of 92 mph (148 kmph) in parts of France and Spain, and even a 129 mph (208 kph) gust recorded in an exposed part of western Brittany. New heat records were broken in the Americas and Caribbean. Brazil, too, experienced some unseasonably hot conditions last month. Likewise, the eastern Mediterranean saw some exceptional heat, with temperatures widely in the high 30s Celsius (around 100F), and Greece recorded its warmest November night on record. At the other end of the scale, North America and Argentina saw some new November cold records. Towards the end of the month, central Australia experienced significant cold spells, while the west was subjected to a heatwave, the station at Bidyadanga recording overnight lows of 29C (84F), the warmest November low on record.

News and discoveries

State of Nature. The latest State of Nature report was published in September and, yet again, painted a rather gloomy picture of the condition of Britain's biodiversity. There's a lot to unpack from the report, but some key take aways were that we've seen a 54% decline in the distribution of flowering plants since 1970, a 19% drop in the abundance of 753 terrestrial and freshwater species, and a 24% decline in seabird abundance. The seabird figure actually masks a larger fall of 49% for 11 species in Scotland. Pollinators decreased in distribution by 18%, invertebrates by 13%, and pest control species, such as ladybirds, by 34%. Of the 10,008 species assessed by the report, 151 have become extinct since 1500, and about one in six species are currently at threat of extinction in the UK.

Welsh red kites are being translocated to Spain in a bid to help boost dwindling populations on the continent. - Credit: Marc Baldwin

Red kite green light. By 1870, the red kite (Milvus milvus) was extinct in much of Wales and absent from England and Scotland, having been the subject of widespread persecution since the 1600s, accused of taking livestock. Conservation efforts started in 1903 and, despite some setbacks, the kite is now thriving in Britain. Our kite population is doing so well that it's now supporting restoration efforts in Spain. Thirty-two kites chicks collected in Northamptonshire by Forestry England and the RSPB are due to be flown to Extremadura in southwest Spain to bolster the declining population. In total, it is hoped that 90 birds will be translocated.

Ambulatory angels. In 2010, the IUCN classified the angel shark (Squatina squatina) as critically endangered, a status reaffirmed in 2019, having previously been considered an abundant species in the Atlantic. Lucy Mead, a Ph.D. candidate at the University of London, is undertaking a study to better understand the behaviour of these sharks. Lucy and her colleagues have recently found, based on acoustic tags fitted to 104 sharks around the Canary Islands, that females maintain small territories but males range both further and deeper than previously thought, routinely beyond 80 metres (260 ft.) and down to 120 m (400 ft.).

Woodland worry. The Woodland Trust estimate that, despite being an immensely valuable habitat for a range of species, only 2.5% of Britain's ancient woodland remains today, having once covered large parts of the landmass. One of the many threats facing the woodland relics is our changing climate, and a new study by ecologists at the Zoological Society or London suggests that that in southern England and on the border with Wales is at highest risk. The data suggest that 62% of ancient woodland is within 100 metres of the forest edge and we think that this puts them at higher risk of the droughts and wildfires that are more prevalent as temperatures increase. Overall, this study suggests that less than one square kilometre of our ancient woods have the potential to be unaffected by climate change.

Seasonal highlight – Reindeer (Rangifer tarandus)

Most children are familiar with this deer species because of its association with Father Christmas, Papa Noël, Santa Claus, Saint Nick, or whatever other name you know him by. Father Christmas' sleigh is pulled by a group of eight magical flying reindeer that are, according to the poem A Visit from Saint Nicholas, commonly re-titled “The Night Before Christmas”, published by Clement Clark Moore in 1823: Dasher, Dancer, Prancer, Vixen, Comet, Cupid, Dunder (from the German meaning 'thunder' but frequently changed to Donner), and Blixem (from the German meaning 'lightning' but frequently changed to Blitzen). You might have noticed that a certain bright-nosed member of the team is missing from this list. Rudolph the Red-nosed reindeer wasn't included until 1939, when Robert May was commissioned by the Montgomery Ward chain of department stores in the USA to create a Christmas poem for a book that was to be given out to shoppers at Christmas as a part of a store promotion. May apparently took inspiration from The Ugly Duckling and his own childhood experiences, during which he was often bulled for being small and shy.

For most people, reindeer are deeply rooted in Christmas folklore, but this is a fascinating and superbly adapted species. - Credit: Marc Baldwin

That which follows is a glimpse into the fascinating world of the reindeer, and I feel Stefan Buczacki summed up the situation well in his 2002 book Fauna Britannica when he wrote:

Outside the month of December, most people in Britain never give the Reindeer a second thought, which is a pity because it is a remarkable beast.”

Home sweet home

The reindeer population in Britain spends most of the year well above the treeline in heather moorland on the slopes of the Cairngorms, 400 to 1,300 metres (1,300-4,230 ft.), before being brought down into lower pastures during the summer to give birth. Reindeer typically inhabit open tundra, although some populations, particularly in Finland, have adapted to mountain forests. Herds living on tundra may migrate vast distances between their inland winter feeding grounds and coastal summer feeding ones. Journeys of 5,000 km (3,100 miles) are known, with herds moving up to 150 km (93 miles) per day. Reindeer are excellent swimmers and will readily cross rivers during their migrations; it appears they can sustain 6.5 km per hour (3.5 knots) in the water and one report suggests they can reach 9.6 kmph (5 knots) when followed by a speedboat!

Reindeer possess a thick double-layered winter coat and fur on their feet that act as insulation, which is of paramount importance for most populations because ambient temperatures on the tundra can drop to -50C (-58F) during the winter. Unusually among deer, reindeer do have fat reserves, but these seem to operate more as a store of energy and vitamins and don't appear to offer much in the way of insulation. So, in addition to their fur, reindeer also have a system of counter-current heat exchangers in their legs and noses to help prevent heat being lost to the environment. The deer's rostrum (nose), for example, is packed with a network of turbinate bones that vastly increases the surface area of the nose. Exhaled warm, moist air passes over the turbinals where it loses heat to the blood and condenses. This heat and water are then used to warm and moisten incoming cold dry air before it gets to the lungs, thus reducing the loss of water and heat during very cold weather.

The way to a deer's heart...

A reindeer eating lichen from a log. During the depths of winter, lichen are a crucial part of this species' diet. - Credit: Marc Baldwin

Deer are ruminants, meaning their stomachs have four chambers, and much of their diet consists of soft, easily digested plant material. Lichens, particularly cup lichens, Cladonia, form a significant part of the diet - more for domestic/semi-domestic deer, which are twice as likely to eat lichens as their wild counterparts, it seems - and are eaten throughout the year, but are of particular importance during the winter. Indeed, lichens, which are high in sugar and thus energy, often form the bulk of the diet during winter. The diet may also include young grasses, birch shoots, flower buds, and leaves during the spring and summer, and fungi during the autumn. Reindeer will also take shrubs, particularly cowberry and bilberry, and sedges according to availability, and can feed on plants that are toxic to other mammals, including wolf's bane (Aconitum), hellebores (Veratrum) and broomrape (Pedicularis).

Although reindeer are primarily herbivorous, they will supplement their diet with animal protein if the opportunity presents itself. Reindeer have been observed scavenging fish and birds' eggs as well as taking chicks from nests and even hunting lemmings in North America. They will also raid human rubbish dumps and actively lick human sweat and human and dog urine, presumably for the salt content. In fact, reindeer will lick salt off roads and drink brackish water, even seawater, the salt providing a noticeable enhancement of antler growth.

Sex and sociability

Reindeer are gregarious by nature and will form herds several thousand strong. A study published in the journal Arctic in 2014 looked at the levels of aggression among reindeer and found that females were less aggressive, and thus more gregarious, than males; female-only groups were larger than either male-only or mixed-sex ones. Intriguingly, the researchers also observed that females in mixed-sex groups were more aggressive than those in female-only ones, apparently a response to the males being generally more pugnacious.

Much of the herd dynamic comes about during the breeding season - the rut - when males actively round up females and try to monopolise access to them as they come into season. A bull's herding expertise influences the herd composition, and a study by Natasa Djakovic and colleagues looked at the kinship among reindeer cows during the rut in Finland. The scientists found that females were more likely to hang out with related females - mums, sisters, aunts - when a mixture of male ages was present than when there were only mature or only young males around. It seems that mature, dominant bulls herd the females more efficiently and essentially control who they socialise with. With more young males around, the competition is greater, and this distracts the mature bulls, allowing the cows greater freedom of association. A study by researchers at Canada's Concordia University, published earlier this year, found similar behaviour in their study herds - bulls actively herded cows during the rut, causing an increase in group size and stability. Low-ranking males, by contrast, had poorer body condition and were less efficient herders, so the females tended to associate with whomever they wanted when the younger males were in charge. So, it seems that, when females have the choice, they opt to socialise with family members, but during the rut they are often constrained by the control imposed by the dominant bulls.

Like most deer species, during the autumn rut males compete for access to females. The rutting behaviour is highly ritualised, involving calling and parallel walking between bulls to assess size/strength. Two evenly matched bulls may clash antlers, each attempting to drive the other back. - Credit: Thorsteinn Petur (CC BY-NC-ND 2.0 DEED)

Reindeer rut during late September and October, and males will antler-clash with one another like other deer species when fighting for access to mates. The bulls attempt to keep the females together in a single herd so they can better protect them from interloping males. Interestingly, the Concordia researchers found that females may stay in the group for most of the breeding season but become choosier at the time of their oestrus, at which point they call more and visit 'satellite' bulls outside the herd.

Once successfully impregnated, the female will gestate for about seven months; if not mated, the cow will continue to cycle every 10-12 days until her oestrous cycle ends. Calves weighing 4.5-7 kg (10-15 lbs) are born between May and July. Typically, only a single calf is born, although very occasionally a cow may produce twins. In 2014, Tilly Smith of The Reindeer Company Ltd., which owns and manages the population of reindeer in the Cairngorms, told me that in the herd's sixty year history they have had only three instances of twins, the first in 1988 and subsequently in 2008 and 2010. Unfortunately, none of the twins survived the birth.

When the cow is ready to give birth, she will leave the main herd and seek isolation. The calf is born with significant deposits of fat called brown adipose tissue around the heart, kidneys, groin and shoulders, which allow it to thermoregulate - that is, maintain its body temperature - from birth. In most populations, the calf is up and following the mother within a couple of hours and the female returns to the main herd a day or so after the birth. Woodland caribou, like most other deer species, hide their calves in vegetation. The calf feeds almost exclusively on mother's milk for the first month or so and then begins to take solid food. Reindeer milk is very rich, with the highest solid content (proteins, fats, minerals and carbohydrates) of any deer milk, enabling the calf to grow quickly. The calf will stay with its mother for its first winter, becoming independent by the following autumn.

Wolves are probably the main predator of reindeer. - Credit: Marc Baldwin

Being large, typically Arctic mammals, reindeer have relatively few predators. Globally, and particularly in North America, their primary predator is the grey wolf (Canis lupus), packs of which will take down adult and young deer. Brown bears (Ursus arctos) and polar bears (Ursus maritimus) will occasionally also take deer of all ages, while wolverines take calves and very occasionally birthing or infirm individuals. Golden eagles (Aquila chrysaetos) will also take calves. Generally speaking, female reindeer tend to outlive males, and may survive for 17 years in good habitat, while males seldom exceed 14 years. The oldest of the Cairngorm herd was 19 years old and the oldest on record that I have been able to find was a female at Brookfield Zoo in Chicago which died in July 1978 aged 21 years and 8 months.

Antlers – biological bones of contention

Antlers are bony appendages that grow from specialised plates on the head called pedicles and, in most deer, are re-grown on a yearly cycle that is regulated by sex hormones. Antlers are the fastest growing mammalian tissue known to science, and complete regrowth of the antlers, which may be highly branched structures a metre (3 ft.) long and weighing 20 kg (44 lbs) in some large cervids, takes only a few months. More details on the growth, cleaning and casting of antlers can be found in my QA.

Most species of deer possess antlers, but ordinarily only the males (and some very old females). Reindeer are unique in that both sexes routinely grow antlers. Interestingly, however, the presence of antlers in the females corresponds closely to snowfall, and the depth and duration of the snow. The more snow the reindeer experience, the more females in the population grow antlers. Conversely, in habitats where winters are less harsh, like mountain forests, fewer females grow antlers, and those that do tend to grow smaller or asymmetrical ones. Habitat notwithstanding, however, there is always a small percentage of wild females that don't ever grow antlers. One study of 3,091 wild and captive reindeer cows in Alaska found that 152 (5%) of the wild population didn't grow antlers, whereas all the captive females did. Male reindeer grow antlers regardless of the habitat.

Unlike most other deer species, among reindeer both sexes grow antlers. - Credit: Marc Baldwin

Before we come to the 'why', let's quickly explore how antlers are grown. Antler buds, which will develop into pedicles, are evident from about the age of three weeks in both male and female reindeer. Unlike other cervids, even castrated reindeer or those with their ovaries removed will grow, clean and cast their first antlers. Normally, castration prevents antler growth in deer. While the antlers are growing, they are covered by a delicate hairy skin that supplies blood. In September, when the antlers are fully grown, this skin dies and peels off in a process known as cleaning or shedding. Once cleaned, the antlers are ready to use during the rut, after which mature males cast during November, remaining antlerless through winter until re-growth begins in February. Larger males cast and start re-growing their antlers earlier than young males.

Non-pregnant females tend to cast their antlers around the same time as the immature bulls, in late winter or early spring, although some young males may retain their antlers until April. Pregnant females, by contrast, often hang on to their antlers until May, casting shortly after giving birth, which is why the presence of antlers in females during the calving season is often used as an indicator of pregnancy rates, although several studies suggest it's not as clear cut as originally believed. One study of 517 female reindeer in North America accompanied by a calf found that about half the cows retained their antlers until shortly after their calves were born, while about one-third had lost one or both antlers on the day their calf was born, and just under 14% were already re-growing their antlers, suggesting that they'd cast at least two weeks before the birth of their calf. So, the moral here is that there's no hard-and-fast universally applicable rule as to when pregnant females cast their antlers.

The rapid growth of the antlers in late winter or early spring puts a substantial strain on deer at a time when they're nutritionally challenged. Lichens are high in sugar but low in protein and minerals, so when the antlers are cast they're eagerly licked and chewed by the deer to regain missing nutrients. Some biologists have suggested that casting antlers during the spring and summer provides a desperately needed source of minerals for the pregnant and lactating cows. Exactly what regulates the antler cycle in female reindeer is still unknown. Several studies have shown that the antler cycle in male deer is regulated by levels of testosterone and oestradiol circulating in the blood. In females, however, the process is less clear. Early authors suggested that it was levels of circulating oestrogen that controlled antler growth, cleaning and casting in the cows because the drop in oestrogen caused by surgical removal of ovaries in non-pregnant females causes premature casting. Similarly, there is a fairly strong relationship between antler casting and parturition, and cleaning of antlers tends to occur close to the onset of ovarian activity, all inferring a hormonal influence. The suggestion was that barren females cast their antlers when their oestrous cycles stop and oestrogen levels drop, while the elevated oestrogen in pregnant females causes the antlers to be retained. A study published in 1997, however, found no correlation between antler mineralisation or casting in female reindeer and their levels of oestradiol (an oestrogen), progesterone or testosterone. The mystery remains.

Why do female reindeer have antlers? Well, a clue is gained from our earlier observation that antler growth in females correlates positively with snowfall. Many reindeer cows are pregnant during the winter and therefore have higher energy requirements than the males and non-pregnant females in the herd. Much of their winter food is buried under snow and the reindeer dig small scrapes through the snow to get at the lichen. It is important that the cows can defend these feeding scrapes from other deer, thus securing as much energy as possible, and this is where the antlers come in. The pregnant females use their antlers to defend their feeding scrapes against others. This is effective against antlerless males, but less so against immature males and other females, both of which have antlers. Larger, dominant females may also pirate the feeding scrapes of subordinates, using their antlers to drive the current owner away.

Growing antlers and retaining them through the winter while bulls cast theirs may help females secure valuable food resources while gestating. - Credit: Marc Baldwin

The use of the antlers only for defending feeding craters, and perhaps also for protecting their calves in the first few days of life (hence many not casting until after the calf is born), probably explains why females don't grow the same elaborate and ornate antlers that males do - they simply don't need them. If the antlers can help the female secure food, that's good enough. Perhaps more importantly, antlers are costly to grow, and females divert a lot of energy and resources into laying down fat and producing their rich milk, so they don't have much to spare on growing antlers. So, antler size tails off in females by the time they reach about three years old, while in males (which do need flashy antlers) they grow in size and complexity until about five years old. Males also continue to invest more in growing antlers as they get older, while females invest less.

Reindeer? In Britain? Seriously?

Yes! Various attempts have been made to introduce reindeer to Britain. Among the earliest was William Hamilton's introduction of a pair on to the Beltrim Castle estate at County Tyrone in Northern Ireland in 1738. The Duke of Atholl subsequently released 14 on to his estate in the Scottish Highlands during 1790. Both attempts ended in failure, as did several further releases by various landowners, despite the deer being released into apparently suitable upland habitat. On the 12th April 1952, however, things were set to change, as eight domesticated reindeer from Jokkmokk in Arctic Sweden flew into Glasgow airport, destined for an enclosure in the Cairngorms. This marked the realisation of the vision of Lapland-born “reindeerophile” Michael Utsi and his wife Ethel Lindgren, who were convinced that reindeer were more useful, easier to train and tastier to eat than our native red deer (Cervus elaphus), and that the Highlands of Scotland was an ideal habitat for them. Following a period of quarantine, the herd were released into a three hectare (300 acre) enclosure near Loch Morlich at Glen More, Aviemore, on the lower slopes of the Cairngorms, in May 1952.

Tourists interact with (mostly feed) the cows, calves and immature bulls of the Cairngorm reindeer herd. - Credit: Marc Baldwin

The project hit several setbacks, including various ailments, one deer drowning in a loch, and the altitude of the first reserve being at too low, resulting in the herd being plagued by flies. In 1954 the herd, then numbering 17, was moved to a larger enclosure on the higher slopes of Airgold Meall (Silver Mount) where they thrived. By 1972 the herd had swelled to 80 deer and ranged over some 60 hectares (6,000 acres) of the Cairngorms and, in 1990, a second herd was established at a site near Tomintoul. Several subsequent introductions of deer - from Sweden, Russia, southern Norway, and the Zoological Society of London - have been made to improve the herd's bloodline. During the winter the deer range over the mountains but they are brought down into pastoral enclosures to give birth, which helps protect the calving cows and their calves from walkers' dogs and from eating litter, which are two of the most significant threat to these deer in the Cairngorms.

Utsi died in 1979 and his wife passed away in 1988. Shortly after, in August 1989, the herd was taken over by Alan and Elizabeth Smith and the deer were no longer culled for meat or fur, instead being used mainly as a tourist attraction and to appear at Christmas events across the country. Today, the Cairngorm population is closely managed by The Reindeer Company Ltd., who maintain the herd at 130-150 animals.

For a round-up of Britain's seasonal wildlife highlights for early winter, check out my Wildlife Watching - December blog. December also marks the month of the Chinese water deer (Hydropotes inermis) rut, and you can read more about their breeding biology, courtship behaviour and other facets of this species' reproduction in my recent articles.

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