Renowned bird author Dominic Couzens
Rising sea levels spell bad news for the Little Tern, whose colonies along our coastlines are already vulnerable to bad weather conditions and nest-destroying humans
explores the fragile world of the Little Tern, a bird whose numbers are sadly declining in the UK.
Somewhere back in the evolutionary history of the Little Tern, something strange happened. Impossible though it sounds, thousands of years ago, a little strand of butterfly DNA found its way into the nuclei of Little Tern cells. Just look at them now. What should be a bird – and a seabird at that – has that unmistakable over-fast flutter, that lightness of body that means that the faintest whisper of wind unsettles its course, yet also has the butterfly’s grim determination to fight the vagaries of the atmosphere. No British bird, even those
smaller and lighter than the Little Tern’s 55g (the same as a tennis ball), demonstrates the same unlikely convergence of movement and mien. It must be genetic.
One of five British breeding terns, the Little Tern is eponymously the smallest and lightest. Its build enables it to be the champion hoverer, and for most birders, that is what we remember: a tiny, white, delicate waif hovering not much above head height (5-7m is normal), often right close in to shore, seemingly too distracted by feeding to notice its admirers. Once it spots food on the surface, the bird will drop
down decisively, making an audible splash as it hits the water.
All the sea terns hover, and there is a delightful subtlety in the different ways they do it. As mentioned above, the Little Tern hovers the most, up to four times more often than a Common Tern. While the Little Tern regularly hunts just a few metres from shore, the Sandwich Tern may do so well out to sea, further from land than the rest. The Sandwich Tern typically hovers higher up (to 10m), makes a decisive plunge and an impressive splash. Common Terns hover less frequently than Sandwich Terns and from less high up (3-8m), but they plummet confidently. Arctic Terns famously have a habit of ‘step-hovering’, pausing on the way down to hover again before finally committing themselves, while Roseate Terns distinctively dive in at an angle, seemingly just flying into the water. These birds are often aiming for the same kinds of fish but have minute differences in their hunting technique.
Strong winds
Fishing by plunge-diving is prodigiously hard work, especially when the stakes are high – for example, when a bird is providing for one, two or three hungry chicks. On such occasions a Little Tern has been recorded making 109 plunge-dives in the course of an hour – as well as 63 visits to the young during the day. For this reason, Little Terns are reluctant to make lengthy commuting runs between feeding site and nest – this can be a matter of tens of metres, while other species such as Sandwich Terns may travel six miles or more to find food. As a result, a Little Tern’s sphere of operation can amount to a remarkably small area.
There are, though, great disadvantages to the Little Tern’s limited horizons. Its need for shallow water – such as along sheltered coasts and lagoons – is strict enough. But it is also uniquely susceptible to the capricious moods of its immediate environment. Hovering is invariably taxing, but in strong winds, which are hardly a rarity along Britain’s coastline, it becomes much more difficult and energy consuming
and above a certain threshold, impossible. Driving rain also makes life difficult. Every coastal bird will also be at the mercy of tides, although these are sometimes kind, funnelling fish along narrow stretches of moving water and aiding the terns in their foraging. In prolonged spells of wind and rain, the Little Tern is at the mercy of its immediate surroundings.
It isn’t just fishing that is affected by the weather. In order to maintain its unusual proximity between feeding and nesting areas, the Little Tern usually breeds along coastal beaches. It can, and does, sometimes lay eggs on sand, but for the eggs’ speckled patterning to work as effective camouflage, shingle beaches are better. In the rain, sand will sometimes adhere to eggs and make it impossible for the birds to turn them, too, so stony substrates, free of vegetation, are preferred.
list of enemies
Imagine, then, a colony of waif-like seabirds, feeding over the mean waves and making shallow nests among flat or furrowed shingle banks. Can you imagine a more vulnerable existence, susceptible to wind, rain, hail and cold, and frighteningly exposed to tidal surges? In Britain, Little Tern colonies are wiped out by unexpectedly high tides at regular intervals – and with rising sea-levels, it seems likely this will happen more frequently.
And what about predators? Little Terns are only half the weight of a Blackbird. Their nests and chicks are protected by nothing more than concealment. Their list of enemies reads like a Who’s Who of seaside and countryside characters – gulls, crows, Ravens, Peregrines, Sparrowhawks, Foxes, Weasels, Stoats, dogs, cats, rats and even apparently benign characters such as Turnstones. A determined predator, even acting alone, can wipe out a colony over the course of a few hours. If this happens beyond the egg-laying stage, that can be curtains for the season. Still, at least Little Terns don’t have to worry about humans, do they? At least humankind, in the warm months of the year, studiously avoids beaches,
We now are the guardians of a paltry 2,000 pairs in the Whole of the uk
especially near calm, shallow water. Yeah, right. There are few birds in Britain that find themselves so threatened by seemingly harmless human pursuits. Just walking along the wrong shingle bank at the wrong time, without a care or bad thought in their minds, humans can cause catastrophic disturbance to tern-kind. Careless dog-walkers are worse, as are those enjoying water-sports, or picnickers, or anglers. People are magnetically drawn to beaches, especially in the summer, and this puts pressure on Little Terns. Amazingly, inexplicably, it is apparently not uncommon for people to destroy nests intentionally – what’s wrong with the world we live in? For this and many other reasons, people and Little Terns don’t mix very well.
They mix so badly, in fact, that Little Terns have been declining in Britain for years and have been of conservation concern almost from the time the term was invented. We now are the guardians of a paltry 2,000 pairs in the whole of the UK and, although the bird itself is very widespread and breeds as far away as Australia, we should really be able to look after our share of breeding terns. Interestingly, the Little Tern is a bird that is remarkably easy to help, not just for a conservation professional, but also for people like you and me. Most of the remaining Little Terns in Britain are in reserves, and local schemes encourage people to help to patrol beaches and keep wayward humans and their pets, and even natural predators, away from the colony. These patrols can be astonishingly successful and raise the numbers of fledged chicks significantly.
Vulnerability
Of course, the Little Tern has evolved a niche that is uniquely vulnerable to human disturbance, and not only that, but also to weather disturbance and destruction by natural enemies. It needs a lot to go well for its breeding season to go well. It needs kind waves, little wind, an abundance of fish, quiet beaches and clear skies. On many occasions, things go wrong.
But that is what we need in our world. We need conditions where the vulnerable can thrive, where the odd toxic breeding season won’t lead to terminal decline. We need a world where the odd human activity can be respectfully restricted, just for the sake of a waif-like seabird. In short, we need a world where a butterfly can fight successfully against the forces of unsteadiness and danger.