Seasonal Update (April 2024)

Gorse (Ulex europaeus) is in peak flower during April and May, the seeds popping in the warm spring sunshine and the flowers filling the air with the scent of coconut. - Credit: Marc Baldwin

Spring began much the same way winter ended - mild and wet. There were a few spring-like days scattered throughout last month, but overall, it was mild, wet, and largely cloudy. Parts of North America, Asia and Africa saw prolonged and record-breaking heat for much of March. It wasn't until after the second week that the grip of El Nino began to fade and we saw temperatures drop in the southern hemisphere. The month ended with what seemed like a hastily named storm, storm “Nelson”, passing through just ahead of the Easter weekend bringing a mix of snow, sleet, hail, torrential rain, and 70 mph winds.

Website update

Two new sections of the water deer article went online last month, covering scent glands and scent marking behaviour. As mentioned in last month's update, I have now completed the article and am turning my attention to revising the existing content. I am currently working on the badger profile.

New and discoveries

New genetic data suggests hybridization between blue (above) and fin whales in the Atlantic. - Credit: NOAA Fisheries (CC-BY)

Huge hybrids. A recent DNA survey of blue whales (Balaenoptera musculus) in the Atlantic has shown some surprising results. The data point to higher-than-expected contributions from fin whales (B. physalus), which suggests interbreeding. Overall, there was positive gene flow among populations in the Atlantic, which is good news, but there are some concerns that hybridization affects the adaptability and resilience of blue whales.

Safeguarding seas. In February, the International Union for Conservation of Nature announced an advance in efforts to protect marine habitats worldwide with the creation of 33 new Important Marine Mammal Areas (IMMAs). IMMAs are portions of the ocean deemed vital for marine mammal survival that can be used as a focus for targeted conservation efforts, and this expansion means than about 70% of the world's oceans are now included.

Bee-team. Bumblebees have long been recognised as clever, social creatures, but a couple of recent studies have shed new light on just how remarkable they are. In one, Queen Mary University of London researchers found that buff-tailed bumblebees (Bombus terrestris) were able to teach one another how to solve a puzzle box. The second, by the same team, seems to indicate that problems too tough for an individual to solve could be cracked with the help of another bee, suggesting complex social learning and cultural transmission.

Elephant graveyard. We know that elephants grieve the loss of loved ones, but recent observations from India suggest that they may also bury their dead. During 2022, the bodies of five elephant calves, aged between three and 12 months, were found in drainage ditches on five tea plantations on the Gorumara Wildlife Division and Buxa Tiger Reserve in northern Bengal. Footprints and dung of various sizes found around the grave sites suggest that herd members of all ages were present at each burial and night guards at the estates reported hearing loud elephant vocalisations, sometimes lasting as long as 30 to 40 minutes, before the herd left the area. Analysis of the carcasses failed to find any evidence of poaching (i.e., no gunshot wounds), most were malnourished, and all showed signs of infection, while bruising along the backs suggested they had been dragged a non-trivial distance to the ditches for burial.

Seasonal highlight – The European adder (Vipera berus)

There's no getting away from the fact that many people are terrified of snakes. In some cases, the fear is valid, particularly in parts of Africa, North America or Australia, and it's not hard to see how humans evolved to give these creatures a wide berth: if one type of snake could kill you, then the safest option, from an evolutionary perspective, would be to consider all snakes dangerous and worth avoiding . In most cases, however, our fears are unfounded and, of the 3,000 or so snake species known globally, only about 15% are sufficiently venomous to cause a problem for a human who gets bitten. Unfortunately, fear tends to breed irrationality, which can all too often lead to persecution of a species or, perhaps worse, a group of species that people have little ability (or desire) to separate. The European adder is no exception and even its name, adder, is derived from the old Anglo-Saxon word naedre, meaning “a creeping thing”.

A male adder (_Vipera berus_), Britain's only venomous snake species. - Credit: Marc Baldwin

In his fascinating, if somewhat depressing, account of the diminution of Britain's wildlife, Silent Fields, Roger Lovegrove described how adders were among the species targeted, with large numbers taken in some parishes during the 1700s and 1800s. According to Lovegrove, farm children in Sussex were paid 6d (pence/pennies) for each adder they killed after the snakes were blamed for biting the noses of sheep, the subsequent swelling apparently leading to suffocation. It's very difficult to get an accurate handle on the level of persecution, because the snakes were often lumped in with general 'vermin' payments, but Lovegrove does cite one specific example where 1,022 snakes, probably including grass snakes and slowworms, were killed between 1714 and 1758 at Tredington in Warwickshire. Here in the New Forest, and likely on other common land in England, there were people who made money from catching and removing snakes, and these appear to have been mostly adders. Henry “Brusher” Mills was something of a New Forest folk hero in the late 19th century. In his forties, armed with a forked stick and a sack, Harry tasked himself with removing grass snakes and adders from local Forest properties. Some were sent some to London Zoo to feed their birds of prey, while other used to make ointments sold as treatment for snake bites and other ailments. Legend has it he caught 30,000 snakes in his 18-year career.

Adders are found in a variety of habitats throughout most of Europe beyond the Arctic circle in the north, south to northern Italy, and east to the Sakhalin Island in the Pacific. Hedgerows, moorland, heathland, bogs and marshes, field margins, parkland and even woodland are all suitable habitats for these snakes, and owing to their requirement for behavioural thermoregulation - moving in and out of sunshine to control their body temperature - they tend most often to be encountered in clearings and along habitat edges. Being so reliant on environmental temperature to support their biochemistry, reptiles are unable to function in persistently low temperatures, although this varies considerably with species and habitat. Adders are the most northerly distributed snake and, as such, are tolerant of relatively cold conditions, but they will enter a hibernation-like state of dormancy (often underground) known as brumation during the coldest months. It tends to be the males that emerge from brumation first, which we think gives additional time to reactivate sexual activity in time for the female emergence. In late spring and summer, the sun's rays are sufficient to warm them quickly, making basking bouts shorter than during autumn or early spring. Indeed, during the summer, basking may be unnecessary, and some recent radio-tracking data suggest adders may continue to be active through the night if temperatures remain high.

A coiled adder, illustrating the striking zigzag patterning on the dorsal surface. - Credit: Marc Baldwin

These vipers are probably our most recognisable snake, sporting a striking black zigzag (or diamond) patterning running the length of the body through skin that's highly variable in colour, including silvery-grey, reddish-brown, greenish-black, or even jet-black skin. Skin colour tends to be more muted just prior to sloughing (i.e., shedding their skin), which they do to grow, with newly shed animals strikingly vibrant. The zigzag stripe terminates at the head in a pattern unique to each individual, allowing identification that can aid scientists studying their populations. Unlike the only other snake species likely to be encountered in Britain and occasionally confused with them, the grass snake (Natrix natrix), adders have a vertically slit pupil, which presumably helps them more strictly regulate the amount of light entering their eye, improving visual performance in bright conditions. (I'm excluding the smooth snake, Coronella austriaca, which is rare and very secretive, and Aesculapian snake, Zamenis longissimus, whose population is highly restricted.) Smaller than most people imagine, males typically grow to about 60 cm (2 ft.), while females are slightly larger, reaching about 75 cm (just under 2.5 ft). The largest adders of which I'm aware were the exceptional animals in a population in Scandinavia that apparently grew to 104 cm (3.5 ft).

Adders hunt for a diversity of prey including mice, voles, shrews, frogs, lizards, newts, and occasionally small birds. Prey is initially tracked using scent, adders sampling the air by flicking their bifurcated tongues in and out of their mouths. Each fork of the tongue is covered in scent receptors, and having a tongue split like this provides a larger surface area for molecular dissolution as well as probably bestowing some direction-finding capability. Prey is stalked to within a few centimetres, at which point the adder coils into an s-shaped loop and launches at the target, biting and releasing the animal in a fraction of a second. Striking distance is typically around half the snake's body length, which is an important consideration when adder-watching. Adders are what we call solenoglyphous (sole-en-o-gly-fus), which means that they have two independently moveable and relatively long (compared to non-vipers) upper maxillary teeth, homologous with the canines of mammals, that are hollow and at the base of which lie comparatively small venom glands. These “fangs” are essentially hypodermic needles used by their owner to inject venom into their target. The venom is a complex mix of peptides and proteins that acts to break down the prey's tissues (i.e., digests the prey internally), although it appears to be haemolytic rather than neurotoxic, which means it generally takes a few minutes for the venom to debilitate the prey. Hence, adders may need to follow a bitten target. Adders, like all snakes, swallow their prey whole using peristaltic waves of muscle contraction to force the prey into their stomach.

A yawning adder, showing the mouth anatomy, including a pair of hinged fangs in the top jaw and the glottis (the tube on the bottom of the mouth), which allows the snake to breathe while swallowing large prey. - Credit: Marc Baldwin

Mating occurs during late April and early May, depending on temperature, and may even continue into June or even early autumn. Males jostle with one another in a what is often referred to as a “dance” for access to females. I have come across a couple of reports suggesting this same method of “duelling” is sometimes used when fighting for access to a kill. Courtship involves a similar parallel “flowing” during which both sexes will flick their tongues and tails. The victorious male mates with the female in a copulation may last several hours and, although a single male may 'mate guard' a female and mate with her several times over a couple of days before the pair separate, males will mate with multiple females during the season.

The female will gestate for 12 to 16 weeks and, as an ovoviviparous species, hold the eggs internally where they'll hatch. Consequently, between three and 20 (typically eight) live young, or young encased in the transparent membrane, each measuring 15-20 cm (6-8 in.) and bearing the trademark zigzag, are born during August and September. The process of reproduction is energetically draining for the mother, and most females will breed only every other year in the UK. The youngsters will often stay with their mother for the first few days after birth, until their yolk sac is exhausted, although in captivity I have seen this association between parents and young (the young lying on the body of either parent) as late as March. The female doesn't offer any 'traditional' parental care (i.e., food provision), however, and the young are capable of hunting for themselves, already having a venomous bite. The juvenile adders may take three or four years to mature, depending on habitat and food supply. The young will shed their skin within a couple of days of birth and feed on nestling mammals, small lizards, frogs, worms, and beetles until they reach about 30 cm (12 in.), at which point their diet matches that of adults.

Adders are often deceptively difficult to track down, even in good habitat, owing to their camouflage and tendency to remain still while basking. Once you've identified suitable habitat look for sheltered spots with good sun exposure. Walk slowly and steadily with the sun on your back, and look for open spots in the sunshine at the base of heather, bramble, or gorse. Early mornings or late evenings tend to be the most productive during periods of prolonged hot weather, while afternoons are often better during the spring and autumn. (When searching remember that snakes are very sensitive to ground-based vibration but largely unconcerned by air movement, meaning they'll flee from harsh footsteps but aren't particularly bothered by noise, such as talking.) Once you've found your subject watch from a distance and never try to touch or pick up the animal. All British reptiles are afforded protection under Schedule 5 of the Wildlife and Countryside Act 1981, which makes it illegal to kill, harm, injure or trade in adders. Generally, an adder will flee when disturbed, but they will sometimes stand their ground, hissing in defence—in such cases, leave the animal alone. If you're successful in finding an adder, or any reptile or amphibian, please record it on the Record Pool.

Although adders can get some moisture from their food, they also need to drink occasionally. - Credit: Marc Baldwin

Cases of humans being bitten by adders are uncommon, and envenomation (i.e., venom being injected, rather than so-called 'dry bites') rarer still. Even when venom is administered, bites are rarely serious, and fatalities are typically linked with the victim suffering an anaphylactic reaction to the venom. If you or a companion is bitten by an adder, it's important to remain calm. The bitten area will likely redden and swell, and the victim may feel faint, dizzy, and nauseous or be sick, more in response to the shock of the bite than to the venom itself. Keep the part of the body that has been bitten still (an arm can be put in a sling if feasible to do so) to reduce the circulation of the venom, remove any jewellery (e.g., watches, rings, bracelets, etc.) that could impede blood flow as the limb swells. Seek medical help immediately, and if it's more than a few minutes to the car call for an ambulance. Keep the patient calm while you wait. Do not remove any clothing or attempt to either suck or cut the venom out of the wound. Additional information about dealing with snake bites can be found in the National Health Service's Treating snake bites article. Adder bites on dogs are more common and much of the same advice applies - try to reduce movement and get your dog to a vet as soon as possible. For dogs, bites to the legs and tail are less problematic than those to the head and muzzle, the swelling from which can cause breathing difficulties. Most dogs recover well from treatment and fatalities are rare, despite what the tabloid press may suggest.

For a round-up of Britain's seasonal wildlife highlights for mid-spring, check out my Wildlife Watching - April blog.

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