Shooting Times & Country Magazine
Banking on the sand martin The bird that nests in cliff faces
Less well known than the house martin, the little sand martin chooses sandy cliff faces to create its nesting holes
When learning to become a bird ringer it is recommended that trainees should acquire as much experience as possible so that they are ready for almost anything when they earn their licences and start to catch birds on their own. My training included catching finches and tits in woodland, rounding up moulting Canada geese, ringing lots of once- common starlings, studying waders on the Wash and making winter roost catches of thrushes. I was also lucky enough to work with a group that met up early on a few Sunday mornings each summer to catch sand martins.
Sand martins are the smaller cousins of house martins and swallows, sandy in colour and very much linked to quarries, where they create their nesting holes in the cliffs created during sand extraction. We were interested in the migration and dispersion of sand martins, as were many other bird ringers across the country. By the time the air warmed up and the first sand martins started to leave their burrows and fly off in search of insects, we had quietly put up a mist net just in front of the cliff face in which the birds nested. Some spotted the net but others would get caught and we would extract them and take the net down. a few birds would already be carrying rings and the others would receive their unique identifiers, rings that they might carry for up to seven years. all of the birds were aged — youngsters have buffy edges to their covert feathers — then measured and weighed.
“Sand extraction companies are tolerant of their feathery squatters, even if they have to change plans”
Sand martins are members of the hirundine family. they are not as well known as house martins and swallows because they do not build their nests under our eaves or in our sheds and stables. traditionally, their homes would have been in riverbanks, but quarrying created similarly steep nesting sites and most now take advantage of these opportunities. Sometimes birds use the same nest holes as in previous years but often they will need to dig new holes when old colonies are turned into building materials and new cliff-faces appear. Sand extraction companies are tolerant of their feathery squatters, ensuring that
colonies do not get dug up during the breeding season, even if this forces a change in their quarrying plans.
Handling sand martins is both a pleasure and skin-crawlingly awful. These are gentle birds — they don’t peck like blue tits or struggle like starlings — but far too many of them carry flat flies that crawl up sleeves and into beards. These flightless hippoboscid flies are hard to catch and even more difficult to kill — even when squeezed between fingernail and thumb. The life cycle is unusual for flies; instead of laying lots of eggs, which hatch into larvae and pupate, a female flat fly produces a single egg inside which is a fully-developed pupa. This is laid in the nest and then pupates over the winter season, waiting for the arrival of one of next spring’s sand martins then crawling on board to suck its blood.
By nesting in quarry cliff faces or in steep riverbanks, often with water below, sand martins make it difficult to get to their nest holes, for bird ringers and for predators. Occasionally, our colony in the Midlands would be built too close to the top of a bank or on a scalable cliff and badgers would wreak havoc, digging out chicks with their sharp claws.
The presence of naïve newly fledged youngsters and busy parents would attract avian predators too, such as opportunist sparrowhawks and specialist hobbies. The hobby is an amazing aerial predator, catching large insects such as dragonflies and small birds on the wing. Sand martins and other hirundines are pretty standard fare for these agile falcons which, with their swept-back wings, can even fly fast enough to catch swifts. Hobbies arrive back from Africa soon after the sand martins each spring and return with them each autumn — wherever it travels, there is usually a hirundine available if a hobby feels peckish.
There are far fewer sand martins in the British Isles than there were 50 years ago. By the time I started catching them in the 1970s, the sand martin boom was over. In the 1960s, there had been a concerted effort by British Trust for Ornithology (BTO) bird ringers, working together as part of a specially funded sand martin enquiry, to try to learn more about the species.
Between 1960 and 1968, about 400,000 birds were caught in colonies and at reedbed roosts, which form in the late summer and into the autumn. The movements of ringed birds revealed a remarkable mobility within the breeding season, with youngsters visiting nesting burrows in other colonies in the weeks after they fledged. Usually these forays were to sites within 80km of the ones in which they had been raised, visits that provided ideal opportunities for adult hippoboscid flies to jump to new hosts and to establish themselves in new colonies.
Huge losses
According to the latest estimates from the BTO, there are probably fewer than 200,000 pairs of sand martins in the UK, compared with an estimated 1,000,000 pairs prior to a sudden crash between 1968 and 1969. Over the course of that winter, droughts in the Sahel — the area that forms the southern boundary of the Sahara — led to huge losses.
A Nottinghamshire study suggests that numbers dropped by 60 per cent between 1968 and 1970. It has been argued that populations were unusually high prior to the crash, fuelled by abundant aphids in farmers’ crops. Vast evening gatherings of birds used to be seen in fenland reedbeds, at the heart of East Anglia’s grain-growing area.
At the end of the summer, sand martins make their way to Africa, generally in hops of 100km to 300km. They travel through Europe then work their way south through coastal countries of west Africa, skirting around the western Sahara before filtering east and into the Sahel. Unsurprisingly, given their small size, and the remote areas in which they feed, the chance of a ringed bird being found in the wintering grounds is very small. We only know as much as we do about these special little birds because so many were ringed in the years when the species was abundant and the focus of so much attention.