Nature’s Top 40: Britain’s Best Wildlife

The hawkmoth most likely to be found as far north as Scotland, and even reaching the Arctic circle, is the poplar hawkmoth. The favoured habitats for this moth are any woodland margins, parks and gardens where the caterpillar’s food-plants of poplar, aspen or willow can be found. The adult has quite broad forewings that are coloured delicate shades of grey, have heavily scalloped trailing edges and a distinctive rusty-red patch at their base. When this quite large moth is at rest, it is very noticeable that the leading edges of both smaller hindwings poke out in front of the forewings – the frenulum is absent in this species – and the tip of the abdomen also commonly curls upwards.

Of course the holy grail of hawkmoth finds must be that of the death’s-head hawkmoth. The name of this most spectacular moth arises from the markings on its thorax, which bear a striking resemblance to that of a human skull and are complemented by the lateral stripes on the abdomen, which add a set of ribs to the image. This moth is the largest species regularly encountered in Britain and has been regarded in many countries as an omen of disaster, a myth possibly perpetuated by being the only known moth species to make an audible squeak when touched! The death’s-head is a native of Africa and migrates northwards into Europe each year, often reaching mostly southern Britain in small numbers by early autumn. The preferred food-plant of the caterpillar is the potato, but they will also help themselves to woody nightshade and jasmine. This is most certainly one species that any moth trapper would be delighted to hear going ‘bump in the night’!

35 Grey seals pupping (#ulink_b2316d15-c7a1-582e-9751-d0a6fb855820)

The autumnal months of September to November are not usually considered the traditional or best time to spend a day down at the beach or on an island-hopping sojourn. But this is exactly the time to visit one of a few special coastal locations if you want to catch up with grey seals as they pup – a tremendous wildlife spectacle that is one of our best-kept secrets and of which Britain as an internationally important player should be justifiably proud.

Seal pups

WHEN

From early September to November depending on the location, with southern and western sites pupping first

WHERE

Monach Isles, Outer Hebrides; Orkney Islands; Donna Nook, Lincolnshire

A pup starts to moult into its adult coat in preparation for a chilly life at sea.

The grey seal is only one of two species of seal that breed along the British coastline, the other being the common seal, which, ironically, is the rarer of the two in Britain’s waters. The wildlife novice can encounter difficulty in identifying these two superficially similar species, but it helps if you know that the grey seal’s wonderful Latin name Halichoerus grypus translates as ‘Hook-nosed sea-pig’! While hardly flattering, this translation goes some way to describing the looks of the greys: their elongated muzzle contrasts with the ‘snub-nosed’ appearance of the more diminutive common seals. Another vital distinguishing feature is the nostrils: in the grey seals the closed nostrils appear like parallel slits; in the common they are splayed to form a V shape.

The size and shape of the grey seal differs between the sexes too. The adult males or bulls are much larger and heavier than the females, with a massive pair of shoulders where the skin over this region and the chest consists of heavily scarred folds and wrinkles. Bulls have a distinctive and convex snout, giving them a ‘Roman nose’ profile, while the females, or cows, look more slender and seal-like by comparison. Although ‘grey’ is a reasonably accurate colour rendition of most of the seals, there is much variation, with some bulls being virtually black, while some cows are creamy-white with a few dark blotches.

It is thought that the grey seal’s historic distribution was in a broad swathe across the entire northern Atlantic, but the advance of the ice during the last Ice Age 20,000 years ago, split the seals into a western and eastern stock. The western Atlantic population can be found along the coast and islands of Canada’s eastern maritime provinces, and, apart from a small relict population in the Baltic Sea, the convoluted British coastline is thought to hold the vast majority of the eastern stock, with current numbers estimated at around 124,000 seals or 40 per cent of the world’s population.

The breeding and mating of grey seals is very much an autumnal phenomenon, and the species is unique in being the only seal that lives in a seasonal environment yet produces its young at a time when the newly independent pups will have to contend with winter storms. It is possible that, being a species that is very vulnerable on the breeding ground, the grey seals have changed their breeding season comparatively recently as a response to prehistoric predation. The peak of breeding also occurs in different months in different parts of the range: pups are born in early September in southwest England and south Wales; from late September to early October in western Scotland; and November at sites on the east coast.

A picture of harmony as mothers and young grey seal pups bond on the beach.

Laurie Campbell

The breeding season begins with the arrival of the sleek, fat females that have spent the summer fattening up on a large variety of fish, of which sand eel, cod and Dover sole are thought to feature heavily. Favoured breeding locations tend to be isolated and uninhabited islands with smooth, sandy beaches; a few choice mainland beaches are also regularly used. In areas with a lower breeding density of grey seals, such as in the southwest of England, caves are often used for giving birth and mating. Close to the time of giving birth, the cows will haul themselves to favoured pupping spots usually about a day before giving birth. These spots vary from the beach just above the high-tide line to a location several hundred metres from the water, such as grassy dune slacks.

Grey seal labour is not very obvious; the birth of the 14-kilogram pup can often occur rapidly, with the first sign being the sight and sound of a host of wheeling gulls as they squabble among themselves for the membranes that enclosed the pup and the afterbirth. Immediately after the birth the cow will sniff and touch the pup a number of times to learn its smell.

It’s Operation Weight Gain as the creamy white pups do their best to treble in weight in less than three weeks.

Andy Rouse

The most startling thing about the newborn pup is its creamy-white fur coat, which is thought to reveal the British grey seal’s ice-breeding ancestry. Further north in the greys’ range, many of the cows still give birth on the ice, meaning the pups are perfectly camouflaged, but, since the retreat of the ice from the British Isles after the last Ice Age, the pups have not been pressurised by predators to change colour and so stand out like a sore thumbs. In a technique still designed to offset predation by swamping the predators, the vast majority of females give birth with a remarkable synchrony, with the result that, on a dense grey seal pupping beach, the white pups can be seen regularly studded along the entire length of the beach with their mothers in attendance.

Initially upon birth, the pups are very poorly coordinated and would suffer quickly from the cold if they were to enter the water inadvertently. The cows stay close to the pups and react aggressively towards any other seals or gulls that come too close, and within a few minutes the pup will begin trying to suckle. Sometimes it takes a while for the newborn pup to locate its mother’s nipples, as they are set towards the tail-end of the body and are usually inverted to aid the seal’s streamlining in the water. However, some gentle prodding from the pup’s muzzle causes the nipples to pop up and it then latches on with its specially indented tongue and begins to suck. Feeding bouts last no longer than about ten minutes on average, and the pup is fed at five- to six-hourly intervals on the incredibly rich milk, which is 60 per cent fat and resembles mayonnaise in consistency. The growth of the pup is slow for the first day but then increases at a phenomenal rate so that the pup will have doubled its weight in the first week. By the end of the lactation period, which lasts between 16 and 21 days, the pup will have increased by an incredible 3 times its birth weight. As the cows feed their voracious pups, they will begin to lose weight in a manner that would have many human mothers green with envy; they lose their rotund shape by shedding four kilograms a day during this intense period.

The bulls generally come ashore when the first pups are born and spend the lactating period competing with the other males for sole access in among groups of breeding females. Like the females, the males do not feed during the breeding season and live off the stores of fat that have been laid down at sea over the previous ten months, meaning that they can devote their entire attention to garnering as many females as possible. For the successful grey seal bulls, size matters, with the largest males, or ‘beach-masters’, often retaining as many as ten cows in their harems. Relations between neighbouring males are often amicable, but they can also result in brutal fights when two evenly matched individuals clash over ownership of the females.

Towards the end of the lactation period, the cows come into season and are then mated with their respective bull a number of times prior to the females leaving the beach and abandoning the pups to their fate. The gestation period of grey seals is only seven months, yet the cows will not be giving birth until they come ashore the following breeding season a full ten months later. They use a combination of suspended development of the fertilised egg and delayed implantation to ensure that the birth will be synchronised to take place at the same pupping beach the following year. Very little is known about where the seals spend their time once away from the breeding ground and they may roam far and wide in order to find the five kilograms of food a day they need to get through the winter.

At around three weeks and just as their mothers begin to leave them, the pups will shed their white fur to reveal the sleek dark coat needed to survive in the sea. It is no surprise that the first few months of life are the most dangerous for grey seal pups, with mortality reaching as high as 40 per cent on some crowded beaches where they can easily starve or be squashed by a careless bull. The process of learning to feed out at sea without any parental help inflicts further casualties, meaning that two-thirds of grey seal pups never reach their first birthday. After this first year, however, their chances of survival become much better, with the cows reaching sexual maturity at around four and living anywhere up to the grand old age of 25 years old. Male seals often do not reach sexual maturity until six, but it is thought that they are not able to hold a position in a breeding group until at least ten, and, even then, will only have a few years at the top before their physical decline leads to them becoming marginalised by the new generation of younger and stronger bulls.

Prior to the Grey Seal Act of 1914, seals were so heavily hunted that numbers in the British Isles were thought to be as low as 500 individuals, but thanks to this and subsequent laws, the population has boomed to a current all-time high of around 124,000 grey seals. While an unmitigated success story for conservationists, grey seals are a contentious issue for fisherman, who see them as competition for fish stocks.

34 Winter high-tide roost (#ulink_93dc301c-fe49-51fd-9573-8269e82df5c8)

The majority of Britain’s highly convoluted coastline that is not made up of either rock or shingle consists of mud, glorious mud. Everyone loves a sandy beach and mudflats are often regarded both with distaste and as a waste of valuable space, but these huge, windswept and seemingly barren areas possess some of the most biologically fertile land we possess. They also play host during the autumn and winter to a huge influx of waders arriving from all points on the globe that take advantage of the muddy microscopic plant and animal life on offer.

High-tide roost

WHEN

August to November, although waders are present all winter

WHERE

The Wash; Dee Estuary; Morecambe Bay; Thames Estuary; Exe Estuary

The retreating tide reveals a smorgasbord of food for the hungry knot.

Mike Lane

It has been estimated that the 155 estuaries around the British coast may well comprise close to a third of the intertidal mud and salt marsh represented in the whole of Europe. These intertidal estuaries are so vital to overwintering waders that they are thought to hold a staggering 1.7 million waders during the winter months, with many more using Britain’s muddy coasts as a refuelling pit stop before travelling on to overwinter elsewhere. This huge figure includes internationally important numbers of knot, dunlin, oystercatcher, redshank, curlew, bar- and black-tailed godwits and grey plover. Many of these species have originated from breeding areas as far away as northern Europe, Siberia, Iceland, Greenland and northeast Canada.

It seems that Britain has become such a ‘winter wader wonderland’ because of our combination of relatively mild winters and large tidal ranges, which ensure that extensive areas of intertidal mudflats become exposed for feeding on a daily basis. Mudflats become formed in estuaries when the discharging rivers slow to such a pace that they lack the energy to transport their cargo of silt any further, causing it to be dumped. In certain estuaries around the British coast, mud has been continually washed down and deposited since the end of the last glaciation, leading it to reach depths of as much as 30 metres. But, irrespective of the depth of the sediment, it is only the surface layers, which are in contact with light, water and air, that support the chain of life from bacteria to algae, and from worms to shellfish, that are ultimately exploited by the birds.

All mudflats undergo the experience of tidal inundation twice every 24 hours as the tide rises and falls, and it is this tidal rhythm that governs the behaviour of all the creatures that live either in or on the mud. The intertidal zone is a harsh place in which to live, as the coming and going of the seawater creates an environment of constant change, resulting in hugely varying temperatures and salinities. Many plants also find it difficult to establish a foothold on the fine shifting sediments; this results in much of the plant material that occurs on the intertidal mud, such as diatoms and algae, being of a microscopic size. These factors also mean that relatively few invertebrates have been able to make a permanent home in the mud compared to those in more stable habitats. But those that do manage to become specialised enough to cope can reach vast numbers because of a lack of competition for the organic material available and the huge amount of substrate (mud) available in which to live and from which to feed.

In addition to mud being easy to burrow into, its structure of fine particles enables the construction of temporary or permanent burrows for lugworms and ragworms, and a variety of shells, such as Baltic tellins and common cockles, in which they can conceal themselves while probing above the surface into the tidal water to feed with specialised siphons and filters. Other creatures, such as Hydrobia snails and Corophium sandhoppers, also emerge from the mud at certain times to graze on the organic debris at the surface; they do so in such profusion that thousands may be present in each square metre of mud.

The best way to appreciate the vast numbers of living creatures hidden in the mud is to watch the multitude of waders that descend to feed on them. These wader flocks will often contain a whole range of species feeding side by side with little or no aggression, as their techniques for foraging are so variable that they will rarely come into competition with each other. As the wader species have no objection to flocking together while feeding, they are able to gain all the benefits of being in a crowd, such as greater security from predation and the ability to exploit patchily distributed food with greater efficiency by noting ‘feeding hotspots’ where other waders are feeding successfully.

With no mud exposed at high tide, the knot and oystercatchers avail themselves of the chance to catch upon fortywinks.

Simon Booth

The diminutive dunlin contemplating where to probe its bill next.

Mike Lane

A feeding bar-tailed godwit – with worm.

Roger Tidman

Waders are thought to find food either by touch, sight, or, in some species, by a combination of the two senses. A number of species take advantage of the fact that invertebrates become more active as they are covered by the advancing tide, so there is often a concentration of birds along the tide edge. Knot feeding here are believed to forage primarily by touch as their bills seek out the microscopic snails and bivalves just below the surface, while godwits visually search either below water or at the tidal edge for the recent casts of lugworms before using their long sensitive bill both to feel for, and extract, the worm. In addition to the birds working the tideline, a number of waders have become specialised at feeding in shallow standing water; these include avocets, which swish their scything bills underwater, and spotted redshank, which upend themselves in a manner more reminiscent of dabbling ducks than waders.

Ahead of the advancing tide, or behind one that is receding, many birds prefer to feed in damp mud because it is easier to probe. The majority of sandpipers, such as redshank or dunlin, feed by scanning the mud to either side of them in walking transects, and, when potential prey is spotted, capturing it either by a peck, if it is a small Corophium snail, for example, or by probing more deeply if it is a buried clamworm such as Nereis. Short-billed birds like grey plovers and lapwings do not tend to use the ‘touchy feely’ techniques of the sandpipers, and rely more on their excellent sight to scan around them for signs of activity while they remain rooted to the spot. When they catch sight of a prey item worthy of capture, they quickly sprint to the spot before it burrows out of their depth. This technique has the advantage that the mud is less disturbed and so does not form a localised ‘prey depression’, which will often happen when the sandpipers are feeding like a miniature herd of grazing wildebeest. When prey activity is low, however, the plovers are not able to begin feeding by touch like the sandpipers, in which case they can resort to a different foraging tactic known as ‘foot trembling’. This technique involves placing one foot on the sediment slightly ahead of the other and rapidly vibrating it up and down, which, it is thought, is meant to simulate the approaching tide, causing their prey to come prematurely to the surface to feed, thereby fatally revealing their location.

Bill length is, of course, very important for determining which birds are able to reach various prey items at different depths, with the curlews’ long sensitive bill being the obvious tool that equips them well to winkle out even the most deeply buried lugworms and ragworms. While birds like dunlin and sanderling are not able to penetrate the mud to the depths of which the curlew is capable, it is thought that they may well possess the ability to use sensors in their bills either to smell or taste the location of prey hotspots.

‘Birds of a feather flock together’, particularly if you are a knot at high tide.