October blended imperceptibly into November, starting mild for the time of year (particularly overnight) but with much of the UK under a blanket of thick cloud. Things improved, however, and the second week saw the return of blue skies along with a cold pulse of Arctic air dropping temperatures significantly during the third week, culminating in significant snow for many. The month ended on a wet and windy note, and it looks like a tumultuous month ahead, with a jet stream that's been strengthened by a cold plunge over Canada energising low pressure systems that are likely to bring periodic strong winds and heavy rain as we head towards Christmas. I wanted to take a moment to thank you, dear reader, for taking the time to sit and read through the updates that I churn out every month and I hope at least some of the new content that has come online over the last 12 months has been interesting. I wish you and your families a merry Christmas and all the very best for the year ahead.
Website news
Two new sections of the Chinese water deer article have gone online, covering senses and their aggressive, submissive, comfort, and vigilance behaviours. Additionally, there's a long-overdue overhaul of the Q&A about hedgehogs and slug pellets to reflect the ban on metaldehyde products that came into effect in 2022.
News and discoveries
Dogging deer conservation. In recent years many countries have seen a rise in the number of feral domestic dogs, and we now have data suggesting they can have a significant negative impact on some conservation efforts. In a short article to the Deer Specialist Group Newsletter in May, Min Chen at the East Normal China University and Shanghai Pudong New Area Forestry Station biologists Haiming Tang and Qiuting Chen described how packs of feral domestic dogs were seen chasing, attacking, and feeding on the carcasses of water deer released at sites in Laogang and Nanhui. Within two months of the deer being released at Laogang, all of them had perished and analysis of trailcam footage and autopsy evidence suggest dogs played a significant role.
Wildlife worries. These days it comes as no surprise to most of us when we hear news about increasing pollution or species loss. The latter was highlighted at a global scale back in October when the Zoological Society of London published their 2024 Living Planet Index. The report is the output of a major effort by ZSL's researchers to assess the population trends for 5,495 species and is used to inform WWF's Living Planet Report. The analysis makes grim reading, highlighting how human activity is pushing Earth's ecology to its limit. The data suggest that the size of these global monitored wildlife populations have plummeted by a staggering 73%, on average, between 1970 and 2020, with the strongest declines (85% decline in species abundance) seen in freshwater habitats. There are some success stories called out in the report, such as mountain gorilla populations having increased slightly and scimitar-horned oryx having been downlisted from Extinct in the Wild to Endangered last year, but it was overwhelmingly bad news. The report points to a multitude of drivers behind these wildlife declines around the world, including habitat degradation and loss, exploitation, the introduction of invasive species, pollution, climate change, and disease.
Great white genetics. An international team of researchers led by scientists in Scotland have conducted the world's first genomic analysis of white sharks. Their data show that the species separated into three genetically distinct populations while modern humans were evolving in Africa, about 200,000 years ago. One population is found the southern Pacific Ocean (Indo-Pacific lineage), the second in the northern Pacific (North Pacific lineage), and the third patrols the waters of the North Atlantic and Mediterranean (North Atlantic lineage). Interestingly, and most importantly from a conservation perspective, the populations appear to interbreed very little, if at all.
Seasonal highlight – The stoat
In 1872 novelist Thomas Mayne Reid wrote of weasels:
“Were they equal in size to lions and tigers, the human race would be in danger of total extirpation: for it is well known that weasels are the most ferocious and bloodthirsty creatures upon the earth.”
In some texts, the terms stoat and weasel are used interchangeably, and when Reid says weasel, he is almost certainly referring to both the “true” weasel (i.e., the least weasel, Mustela nivalis) and its slightly larger cousin, the stoat (Mustela erminea), which is also known as the short-tailed weasel. This month, in the last of these seasonal species highlights, we take a whistle-stop tour of the natural history of this deceptively diminutive carnivore.
Villain of the piece?
It's safe to say that stoats and weasels have generally been portrayed as the bad guys in popular literature and, more generally, to refer to someone as a weasel is not typically a sign of endearment or affection. Indeed, the Merriam Webster dictionary notes that the word weasel is often used to identify “a sneaky, untrustworthy, or insincere person” and, in Charles Dickens' 1841 tale The Old Curiosity Shop, Mr Quilp described himself as “cunning as a weazel”. Similarly, most of us are familiar with Kenneth Grahame's children's classic The Wind in the Willows, published in 1908, in which “skirmishing stoats and bloodthirsty weasels” laid siege to Toad Hall and weasels with guns jeered Mole dressed as a washer woman. Ratty said of these creatures:
“Weasels - and stoats - and foxes - and so on. They're all right in a way ... but they break out sometimes, there's no denying it, and then - well, you can't really trust them, and that's the fact.”
A slightly more macabre picture of the stoat has been painted in folklore and, in the second volume of their Encyclopædia of Superstitions, Folklore, and the Occult Sciences of the World, Cora Daniels and Charles Stevens note how stoats were once believed to hold the souls of infants that had died before being baptised. More generally, encountering a stoat during your journey was an omen of bad luck that could only be neutralised by greeting the stoat as a neighbour.
Despite their generally bad press, it hasn't been all bad news for the stoat - they were held sacred by the Komi peoples of north-eastern Russia, and revered by the ancient Iranian religion of Zoroastrianism. Furthermore, in a hilarious episode of the BBC sitcom Bottom, Smells, first broadcast in September 1991, Richie (played by the late, great Rik Mayall) used the word stoat in an attempt to come up with a lonely-hearts advert to elaborate his sexual prowess:
“Foxy stoat on the prowl…rawwwwl…”
The truth about the stoat is, however, ultimately much more entertaining than the fiction.
A stoat by any other name
Stoats belong to a group of mammals known as the mustelids. That is to say, they're members of the Mustelidae family (from Latin mustela, meaning 'weasel') along with some other familiar species including otters, badgers, weasels, and ferrets. From nose to tail tip, stoats grow to between 25 cm and 40 cm (10-16 in.)—the tail can be one third or more of the total body length—and males grow larger than females. In Britain, male stoats average about 39 cm (15 in.) in length and average about 367 grams (13 oz.), while females average 35 cm (14 in.) and average 242 g (8.5 oz.). Size is the only sexually dimorphic character in stoats, making it almost impossible to determine sex without a rather intimate inspection of the animal.
Stoats and weasels are often mistaken for one another and, despite the old joke of the two being 'weasel-ly separated because stoats are stoat-ally different', it can be difficult even for the experts to tell the two apart without a good view. Most encounters are brief glimpses as the animal darts across a track, or into some long grass, making identification all but impossible. Both stoats and weasels exhibit the same slender form, short ears, and chestnut-brown fur on the back, flanks and tail, with white fur on the belly. Seeing the two side by side makes the situation a little easier, because stoats are significantly larger than weasels. An adult male weasel will weigh only about one-third that of an adult male stoat and measure about 25 cm (10 in). If a clear view is possible, the most definitive method of separation is to look at the tail: the tail of a stoat is much longer in proportion to the body (i.e., about one-third the body length) than that of a weasel (about one-fifth body length), and a stoat's tail has a dark black tip, while that of a weasel is a uniform chestnut-brown colour.
Punching above their weight
The slender body and short ears of the stoat are indicators of how it has evolved to hunt. When other predators (foxes, for example) set their sights on a vole or rabbit, the chase is generally over if the prey makes it to a burrow - the same is not true of a hunting stoat. Stoats evolved a sleek, fusiform profile to enable them to follow their prey down into their tunnels, and a stoat is quite at home hunting rabbits and rodents underground. While being small and slender confers clear advantages in terms of being able to hunt where most predators can't, it also has its disadvantages. Perhaps the most significant drawback is the high metabolic rate. With a resting heart rate of about 390 beats per minute (you, while sitting reading this, will probably have a heart rate of about 70 bpm), stoats need to consume about 20-30% of their body weight per day, making them very susceptible to starvation during food shortages. Stoats also appear to store excess energy as muscle mass rather than fat. Fat would soon prove an issue for an animal that relied on being slim to get along narrow vole tunnels, but this lithe frame means that they can suffer badly during particularly cold spells because their small size means they lose heat rapidly and have very little fat to serve as insulation or a fuel reserve. The result is that stoats are voracious predators, active throughout the year.
Unsurprisingly, given how difficult this species is to study in the wild, most of the data we currently possess on the food preferences of the stoat come from analysis of stomach contents and droppings. This method of dietary assessment is understandably biased towards remains that make it through the digestion process in an identifiable condition (stronger bones, claws, fur and so forth) and can underestimate the presence of things such as soft tissues and eggs in the diet. Nonetheless, in most studies, rodents and rabbits constitute more than half of the diet. Stoats will also prey on small to medium-sized birds (including gamebirds, domestic poultry and ducks), eggs, frogs, and various insect species. In common with many carnivores, stoats will cache surplus prey (i.e., bury it for later retrieval) and may exhibit the same “surplus killing” behaviour observed in foxes if they gain access to a chicken coop or rabbit run. Stoats are capable climbers and swimmers, meaning that little is out of their reach.
It seems remarkable that an animal the size of a stoat could routinely prey on something as large as an adult rabbit, which may be nearly thirty times its own weight. More impressive still is that the stoat can pick up the rabbit and run off with it, in a manner that Carolyn King and Roger Powell described as “looking like a terrier bounding off with a sheep” in their 2007 opus, The Natural History of Weasels and Stoats. Stoats can achieve this because they are proportionally stronger than many larger carnivores. Being small conveys mechanical advantages, as you've probably seen in insects such as ants or stag beetles carrying many times their own body weight. I won't go into the mathematics—there's an interesting book on this subject called Scaling: Why is animal size so important? by Knut Schmidt-Nielsen if you're interested—but suffice to say that, in mammals, a muscle fibre of a given width has the same “pulling power” regardless of whether it's in a stoat or an elephant. As mammals get larger their muscle mass increases, but so too does the mass of the skeleton that they must move around; and skeletal mass increases disproportionately to muscle mass. In other words, the mass of the skeleton is proportionally much less in small mammals than in larger ones, which means that a lump of muscle of a given size exerts more impact in smaller mammals than big ones. This scaling relationship gives stoats the apparently supernatural strength that allows them to carry away prey much larger than themselves.
Lean, mean, underground hunting machine
Stoats have highly acute hearing, the sensitivity of the ear enhanced by a large cavity in the middle ear called the tympanic bulla. Studies in the wild have demonstrated that stoats are able to clearly hear the ultrasonic squeaks of voles and other small rodents, and that their sensitivity to low frequency sounds, such as the stomping used by rabbits to convey danger to other members of the warren, is better than would be expected given their size. I haven't seen any data for stoats, but University of Illinois zoologist Bruce Gillingham investigated which senses played the biggest role in the hunting of the weasel. Studying five weasels in a controlled enclosure, Gillingham concluded that the animals hunted primarily by sound, with smell and sight being relegated to second and third place respectively, which is expected given the restrictions of subterranean activity. Additionally, while underground and in dense cover, stoats employ vibrissae (whiskers) to find their way around and detect movement in air currents produced by their quarry.
The complex structure of the turbinal bones in the nasal cavity of stoats suggests that they have a good sense of smell, although I know of no specific studies on the sensitivity. Regardless, scent plays an important social function, used to identify individuals and mark territory borders, and stoats have large anal glands and a series of smaller scent glands on their cheeks, stomach and flank, all of which are used for scent-marking.
It appears that stoats have a reasonably good sense of sight although, in common with most non-primate mammals, it's geared more to the detection of movement than to high resolution imaging of their surroundings. Stoats have a duplex retina, which means it has both cone cells for bright/colour vision and rods for low-light vision, and behavioural experiments from the late 1950s suggest the potential for limited colour vision in this species; it appears that they can distinguish red objects and possibly also yellow, green and blue. Stoats and weasels have horizontally slit pupils, which can close more tightly in bright light than our rounded ones, making them are less easily dazzled and allowing them to hunt over a range of light conditions. A layer of cells behind the retina called the tapetum lucidium reflects light that would normally be lost back into the eye to enhance vision in low-light conditions—this is also what gives stoats their vivid green eye-shine when caught in the beam of a torch, headlight, or camera flash.
A stoat's life
Stoats are a fairly fecund species, producing larger litters than most other carnivores. Mating occurs from April to July and ova are fertilised as normal but, in common with only a handful of other mammals such as the roe deer and badger, the embryo stops dividing at the blastocyst stage (when it is a small ball of about 200 cells) and remains in “suspended animation” during the autumn and winter. The blastocyst will implant in the uterine wall during the following spring and development will continue as normal - this process is known as delayed implantation or embryonic diapause and means that kittens can be born earlier in the year and thus have longer to grow and develop their hunting skills before the winter. Once implantation has occurred, the female will produce a single litter of about nine kittens (up to 13 have been recorded), each weighing 3-4 grams (about 0.1 oz.), after a gestation lasting four weeks. Soon after the kittens are born, the female will come back into oestrous and draw the attention of local males.
The peak month for births in Britain is April and the kittens are born blind, deaf, toothless, and covered in a fine, pinkish-coloured fur. The female will raise the kittens alone. They will suckle for about 12 weeks but will start taking solid food at around four weeks, shortly after their milk teeth have erupted. The kittens' eyes open at about five weeks and fur growth is sufficient to allow them to maintain their body temperature by eight weeks (prior to this, if the female leaves the nest, the kittens must huddle together for warmth). The black tip on the tail has developed by about six weeks of age and the innate hunting behaviour is visible at around ten weeks. Once the kits reach about 12 weeks the family starts to break down and the kittens begin dispersing. Just prior to dispersal, family groups of stoats can be seen running, jumping and playing together. Female stoat kittens are sexually receptive staggeringly early and can mate from only three weeks old, while still blind and deaf. One Russian study reported that a female kitten mated by an adult male at 17 days old gave birth to, and successfully raised, a litter of 13 kittens after 337 days (note that this period includes the delayed implantation). Male stoats aren't sexually mature until about 11 months of age.
The average age at which most wild stoats die is between 11 and 16 months and few stoats will live to see their second birthday (only about 7% in some populations). The oldest wild stoat on record lived to be just under five years old, while the record longevity in captivity was a female born in a private zoo in Russia in 1984 that was released in 1995 at the ripe old age of 11 years and two months.
For a round-up of Britain's seasonal wildlife highlights for early winter, check out my Wildlife Watching - December blog.