Seasonal Update (December 2020)

The New Forest in mid-December. - Credit: Marc Baldwin

Wet, windy and especially mild conditions saw out October, ensuring the second mild Halloween in the space of a few years. According to Copernicus ECMWF's records, October was, globally, the third warmest on record, just behind 2015 and 2019. Indeed, the six warmest Octobers on record have occurred in the last six years.

The unsettled weather continued into November, with storm “Aiden” bringing 80mph winds to Ireland and, a day later, 60mph winds to the south coast. Strong winds were a feature of the first half of the month along with warmth – parts of eastern England woke up to temperatures of a remarkable 18C (64F) on Monday 2nd November. Indeed, bar a couple of short cold snaps lasting a day or two, November was mild and wet.

A cold front swept through that was proceeded by a ridge of high pressure, bringing settled conditions and also a significant temperature contrast across the UK. Night-time temperatures fell away widely across the south of England for a couple of days. On Thursday 5th temperatures on the south coast hovered just below the seasonal average at 11C (52F) courtesy of an air mass from Canada, while Durham recorded 18C as it basked in Bahamian air.

The final month of autumn was unseasonably mild for much of England and Wales, with overnight lows of 18C/64F in the first week of November. - Credit: Marc Baldwin

The second week of the month saw temperatures widely back up to 16C/61F, 18C in Wales, with night-time temperatures quite mild for the time of year at 10-14C (50-57F), the seasonal average being 5-6C (~42F). Much of Europe experienced warmer than average weather last month, too, with a historic Nordic heatwave - Gladhammar in Sweden, for example, recorded 18.4C (65.1F) on 6th November, the highest November temperatures in at least 50 years. Accompanying the mild conditions was widespread and dense fog. A wet and windy (92mph at The Needles off the Isle of Wight) middle weekend ensued, followed by a few more mild days before the airflow switched to a northerly, bringing temperatures back down to around the seasonal average leading into the third weekend.

The final week of November started wet and windy across the north west of the UK, but mild and grey in the south and east. The second half of the week saw the prevailing south-westerly airflow replaced by an easterly wind, bringing colder air from northern Europe and dropping temperatures just below the seasonal average, with widespread fog and frost across most of the country, although the south and east were still bathed by warm continental air – on 28th November we were still seeing highs of 15C (59F) in Eastbourne, for example. At the time of writing, the Met Office are predicting high pressure to build over Scandinavia, bringing cool but dry conditions for December.

Outside of Britain, Australia has been in the grip of a profound and widespread spring heatwave, with overnight lows of 29C (84F). Indeed, a new record for the warmest November (late spring) was set when the mercury hit 46.9C (121.3F) in Smithville, New South Wales on 28th November.

I’ve seen several posts on social media recently asking whether it’s unusual to see hedgehogs around in late November. The answer is: not really. If the weather remains reasonably mild (certainly double digits) overnight and food is provided, it is not unexpected that some hedgehogs will continue to visit. In our garden, most of our hogs stopped visiting in early November, despite it subsequently getting very mild, but a few have continued to user the feeder (and have been caught on the trailcam collecting nesting material) into the beginning of this month. It is, however, too late in the year for small hedgehogs (i.e. those <550g) to put on sufficient weight for hibernation and they will need help. Our local rescue has also seen a virulent strain of fluke affecting autumn orphan hedgehogs this year, too, so even if they look fairly healthy they may well be suffering with a high parasite burden, causing them to lose weight.

If you’re interested in the wildlife to be found this month, including the peak of the Chinese water deer rut, wader season and the truth behind the plant no office Christmas party is complete without, check out my Wildlife Watching - December page.

In the news

A few recent stories in the news that caught my attention include fruit bat family dynamics, the UK’s waning biodiversity targets, and how birds tell their chicks about the weather even before they’re out of the egg.

New research from Java suggests that farmers' irrigation pipes may help connect fragmented forests for slow lorises. - Credit: Vladimir Buynevich (CC BY 2.0)
  • Family first? If this past year has taught us anything, it’s the importance of family, but kin harmony doesn’t come easily for everyone and it seems we’re not the only species who actively avoid relatives. A new study by zoologists at Masaryk University in the Czech Republic found no relationship between relatedness and roost sharing among their Egyptian fruit bats suggesting that, unlike many mammals, this species don’t preferentially roost with their relatives.
  • Biodiversity bombshell. In a sadly familiar scene, the recently published UK Biodiversity Indicators 2020 report has highlighted how the UK is failing on its long-term biodiversity targets and is experiencing a “relentless” decline in wildlife. According to the report, 14 of the 24 biodiversity indicators show long-term decline.
  • Slow loris pipe dream. Researchers studying slow lorises on Java, the world’s most populous island, have recently reported success in using local farmer’s irrigation pipes suspended in the trees to help connect the habitat for this critically endangered primate. The classic rope ladders that have been used successfully with other primates don’t work with lorises but monitoring by camera traps showed that the lorises started using irrigation pipes as tree-top bridges as soon as 12 days after their installation.
  • Educating embryos. We know that babies in the latter stage of development respond to external stimuli and can be influenced by things such as the music played by their mother. It seems that birds also pass on information to their chicks while they’re still in the egg. Researchers used microphones to monitor 125 zebra finch nests and noticed that parents sang very specific songs when alone with the eggs. Of particular interest was that the birds sang one particular song only when the weather was warm and their chicks were close to hatching. The scientists suggest that the parents are passing on information about the weather to their soon-to-be-born chicks.
  • Rainforest razed. The latest annual PRODES data, which calculates forest cover based on satellite imagery, suggests that deforestation in Brazil’s Amazon rainforest has increased to a 12-year high, rising 9.5% on last year’s loss to a staggering 11 thousand hectares (2.7 million acres) in only 12 months. Brazil’s President Jair Bolsonaro has encouraged the clearing of rainforest for agriculture since he came to power last year.

Website news

Research continues for the article on the Chinese water deer, which I hope to make a start on writing early next year. Elsewhere, some minor updates have been made to the hedgehog article, the nests and hibernation sections in particular, and a new Speed Read went live earlier this month covering the Hazel dormouse.

Discoveries of the Month

You are what you eat? Is changing diet leading to changing jaw morphology in red squirrels?

The idea that the food we consume has an effect on the behaviour and morphology of our bodies is well known and applies widely across the living world. We know that crocodiles in zoos, for example, often tend to have more subcutaneous fat than those in the wild. A similar scenario is observed among foxes living in our towns and cities, where an abundance of high energy food is available year-round. In some cases, these body changes may be relatively innocuous, resulting in fat that can be lost later, but there are some changes that may be overall more significant and perhaps even affect what an animal is subsequently able to eat.

Squirrels are familiar garden visitors and many people enjoy feeding them. Being rodents, squirrels have a pair of robust incisor teeth that grow throughout their lives, kept in check by their sempiternal gnawing. Over millennia the squirrels’ skull and dentition, what we collectively term “cranio-mandibular morphology”, have evolved to meet the challenges of even the toughest nuts they’re likely to encounter. Now, new research from a team of UK and US biologists suggests the trend may be going in the opposite direction.

Squirrels have evolved teeth, skull and jaw morphology to tackle a wide variety of tough food. - Credit: Marc Baldwin

The research team, led by Philip Cox at the University of York, studied the skeletons of 258 red squirrels, submitted from across the UK, in the collections of the National Museums Scotland. The aim of the study was to determine whether Britain’s red squirrel populations differ from one another in their cranio-mandibular morphology and, if so, in what ways. To do this, they measured a host of skull and jaw features and submitted them to statistical analysis to look for trends. The results are currently in press with the Journal of Zoology.

The data show significant differences in the mandibular (lower jaw) morphology and biomechanical estimates both within UK populations, and between British and continental squirrels. Squirrels on Formby and Jersey were very close in terms of mandible size - but they, along with squirrels in Germany, were all significantly larger than most other populations. Of particular interest was the finding that the mechanical advantage, the efficiency with which jaw configuration and muscle power is converted into bite force, was lower in Formby and Jersey subjects. In other words, they appeared to be less efficient gnawers than squirrels from elsewhere in Britain.

The authors suggest that the change in the mechanical advantage of squirrels on Formby, and to a lesser extent Jersey, may be a response to a proliferation of peanuts in their diet. During his studies at Formby in the mid- to late 1990s, Colin Shuttleworth found that peanuts were provided by both the National Trust Centre and many local residents. While largely discouraged now, at one point peanuts made up nearly 60% of the squirrels’ diet. Peanuts are much less mechanically resistant than hazelnut or pine seeds and the suggestion is that the mandibles may have changed in response to this less demanding food. If this is the case, Cox and his colleagues caution that diet must be a significant consideration for squirrel conservation projects:

If supplemental feeding is to some degree implicated in changes in mandibular morphology that reduce the efficiency of gnawing, then diet must be taken into consideration in captive breeding and during translocations. The results here suggest red squirrels may not thrive if moved to a habitat with a more mechanically demanding food source, or if supplementary feeding is withdrawn suddenly.”

Source: Cox, P.G. et al. (2020). Morphological and functional variation between isolated populations of British red squirrels (Sciurus vulgaris). J. Zool. Early View. doi: 10.1111/jzo.12829.

Enter the sand-hog. New insights on hedgehog hibernation in captivity

Hedgehogs are unquestionably one of Britain’s favourite small mammals and I find it‘s a common theme these days that whenever I bring them up in conversation, someone invariably says “I’ve not seen one in ages, they used to be everywhere when I was a kid”. It is now a well-recognised problem that hedgehog populations appear to be undergoing a steep decline, despite the diligent efforts of an army of mostly unpaid and perpetually exhausted carers across the country. Most of us also know that hedgehogs tend to disappear during the winter months as it gets colder and their food supply dries up, but we often expect that there are some hard and fast rules around this hibernation – hedgehogs “bed down” in November and we shouldn’t see them again until April. The reality is quite different, however.

Much of what we know about hedgehogs during hibernation comes from radio-tracking studies of wild individuals and animals kept in laboratories where they can be closely monitored. We actually have relatively few data from hedgehogs kept through winter by carers and wildlife rescues. A recent study of hedgehogs overwintered at Prickles and Paws Hedgehog Rescue near Newquay, Cornwall, has shed some light on how hogs undertake hibernation when given ad libitum access to food, and how this affects their weight loss over the winter.

Hedgehogs are poorly insulated mammals and this is one reason they need to hibernate in temperate regions. - Credit: Marc Baldwin

During the winters of 2015/2016 and 2016/2017, 35 healthy adult hedgehogs were monitored during hibernation. A hog was considered to have started hibernation on the first night it didn’t leave the nesting area and to have exited hibernation after five consecutive nights of activity outside the nest. The duration between each arousal was measured, along with any food eaten and the weight of each hog.

All the individuals hibernated, although there was significant variation in the durations; between five and 111 nights. The researchers also noted variation in the number of arousals, with one animal waking up 15 times over the winter of 2015/16, while three others woke up six times. Typically, hogs woke for less than two days, although some were active for up to nine nights. It should be noted, however, that arousal was only counted if the hedgehog left the nest; so if it woke up but remained in the nest (which we know some do in the wild) it was recorded as continued hibernation. The longer the hibernation period, the more periodic arousals there were, but even despite this the less time the hedgehogs were awake in total.

Most hedgehogs lost weight through the hibernation period, but four actually gained, suggesting that they fed during arousal periods. Of particular interest here was the observation that it was the duration asleep, rather than the number of arousals, that correlated with weight loss. This is noteworthy because we tend to consider “waking up” to be probably the most energetically expensive part of hibernation. Overall, they found that the larger the hedgehog, the more often it woke up during hibernation, but the less weight it lost, and this may be a response to food being available the whole time. Indeed, in their paper to the journal Animals, published in August, the researchers suggest that provision of food can be a positive element for hogs hibernating in captivity:

Availability of food in captivity appears to reduce the amount of weight lost during hibernation; at least, those individuals that woke (and thus could feed) more often lost less weight per day than those that woke less frequently. If arousal is energetically expensive, but necessary for other physiological reasons, then these costs can be offset by eating. Food should certainly be made available for hedgehogs hibernating in captivity for consumption during periods of activity, to help offset weight-loss and improve likelihoods of surviving hibernation. The possibility that availability of food is encouraging shorter hibernations and more frequent, longer arousals requires greater investigation.”

A hedgehog collecting leaves for a nest in a hedgehog house. It's relatively uncommon for adult hedgehogs to overwinter in hedgehog houses and what little tracking data we have suggests they're more useful to youngsters. - Credit: Marc Baldwin

A logical extension of this idea is that continuing to provide a small amount of food in your garden through the winter may also offer a valuable “refuelling station” for wild hedgehogs during periodic arousal.

Source: South, K.E. et al. (2020). Hibernation patterns of the European hedgehog, Erinaceus europaeus, at a Cornish rescue centre. Animals. 10: 1418. doi: 10.3390/ani10081418.

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