Whose tern is it to watch today?

The birds are little terns, a species that truly earns the family’s nickname of sea swallow, and there is no rarer nesting seabird in the UK. Their tiny colony on the Yorkshire coast is the only regular breeding site between the Tees and Norfolk, and from April to August it is surrounded by a formidable electric fence packing a 9,000 volt punch to anyone or anything that tries to reach the nests.

The colony houses between 25 and 30 pairs and last year they successfully fledged 19 chicks. But they are at constant risk from the moment the eggs are laid in early June until the young birds have learned to fly and are able to set off on their southerly migration in August.

The bird is the UK’s smallest tern, and has a distinct yellow bill with black tip, and a short tail. It is in long-term decline around European shores, making it an amber-listed species – the second-highest level of international concern by conservationists. Less than 2,000 pairs breed in the UK, most in Scotland but with significant colonies in Cleveland, East Anglia and Hampshire.

Paul Collins, the warden of Spurn Bird Observatory who has supervised Yorkshire’s little tern project for the last nine years, says the main threats to the colony come from predators.

“There’s always something that wants to eat the eggs or chicks. Foxes are one of the biggest dangers, which is why the electric fence is essential. If a fox gets in when the eggs are on the ground they can wipe out the entire colony in a single night. Foxes are very clever, and if one of them is really starving it’ll somehow find a way in, so we hope the vole and rabbit population of this part of the coast is good enough keep the foxes from going hungry.”

In addition to the electric fences foxes are deterred from accessing the sand dune colony by the use of battery-operated cat scarers, which emit a high-pitched noise and are usually deployed to keep domestic cats away from bird feeders in gardens.

Last year Paul tried a more unusual method of fox control – lion dung. “I was told that because the lion is top of predator world, it’s supposed to put off smaller predators.

“Someone at the RSPB got a supply of lion dung from a zoo somewhere. I‘ve no idea if it worked, but what I do know is it wasn’t much fun taking up to the colony. It’s really smelly stuff.”

The other main predator during the egg stage is crows, and so far the only way that’s proved possible to stop them wreaking havoc is by the duty warden shouting and clapping their hands until the crows fly off.

Occasionally, a merlin – the UK’s smallest bird of prey – may pass down the coast and prey on the chicks. More often the threat comes from kestrels when the chicks are very small. Last year, the Teesside colony of little terns lost all its chicks to a pair of kestrels. Each fence post around the Yorkshire colony has an upturned and sawn-off plastic bottle attached, so that kestrels and merlins cannot use them as perches for watching the colony.

Even if they survive the threats from predators, the terns’ habit of building their nests fairly close to the edge of the sea makes them vulnerable to high tides.

Sometimes there’s a threat from humans. Egg collectors who find the location are put off by the formidable electric fence, and there’s a system of taking the registration numbers of suspicious vehicles. This is helped by the proximity of the North Sea Gas Terminal at Easington, with its 24-hour Ministry of Defence police patrols.

Lizzie Bruce, one of the two tern wardens employed to guard the terns through daylight hours, had to deal with a couple who let a child to throw stones into the colony. She said: “They were the kind of people that no matter what you said to them they wouldn’t tell the child to stop. I tried talking to them but their attitude was that they couldn’t see why money was being spent on bird conservation when it could be spent on children.”