Why do sand martins sometimes reject last year's nest burrows?

Irish Examiner

01-05-2025

Ní féidir leis an gabhlán an dá thrá a phreastal (literally means 'the sand martin can't be on two beaches'... you can't do two things at once)
Having crossed Pharaoh's hot dry ocean, 'my' sand martins are back from Africa. About 30 pairs nest each summer in a soft bank facing the sea, close to my home. The little migrants are weighing up their options... they deemed the site unsatisfactory last year and moved on. Will these temperamental breeders reject it again this time around? Fingers crossed!
Some positive news. The Sand Martins have arrived @stwater Minworth and are showing interest in The Sand Martin Hotel we built. Great to get active footage on our @tjfocus_ @SpypointCamera Trail Cameras. The paint job seems to have done the trick pic.twitter.com/V3Q6lZfWbS — West Midlands Ringing Group (@RingersWm) April 17, 2025
Like all creatures great and small, a 'gabhlán' faces life's two big challenges — to eat without being eaten, and to beget youngsters who will carry the genetic torch on to future generations. Success hinges on risk assessment. Humans are changing the environment, relentlessly presenting new challenges. A bird might give people a wide berth, as whooper swans do. Or, like mute swans, it can exploit the environments that humans create.
Other members of the swallow family made such a choice long ago. The cave and cliff nests of old were abandoned. House martins took to building under the eaves of buildings. These squatters, however, remain outdoors. Swallows are cheekier — they nest inside barns and cow-sheds. Only the sand martin has remained true to its age-old traditions. It continues to dig tunnels in banks as it always did. Sand quarries and holes in sea-walls are our only gifts to it.
The How to Build Guide booklet has arrived and is free of charge. DM me if you're interested in a copy. It's also available at the link below. https://t.co/xqWRQsVWxy pic.twitter.com/8CujVsttPC — Sand Martin Wall (@SandMartinWall) October 11, 2022
'Gabhláns' have a bunker mentality. Each pair digs a tunnel. The nest chamber, a human arm's length or so underground, is safe from enemies. Only an opportunistic stoat can penetrate a burrow. Badgers were recorded digging up nests in Sweden.
Burrows from previous years might seem serviceable to our eyes. Digging a new one can take up to two weeks, so renovating an existing tunnel should be labour-saving. Martins are plagued by feather-lice and creepy-crawlies. Are they fearful that old nest-holes might still harbour the eggs of previous tormentors?
Sand martins are gregarious — they roost nest and migrate together.
Like their cousins, sand martins are gregarious. They roost nest and migrate together. Breeding colonies, typically, have up to 50 pairs. There is safety in numbers. The hobby, a very scarce visiting falcon, has a particular penchant for martins but a swirling flock of angry parent sand martins will mob it, driving the predator from the colony.
But there are downsides to communal living. A sand martin 'village' is conspicuous; it can't be hidden from prowling enemies.
Breeding colonies of sand martins typically have up to 50 pairs. There is safety in numbers.
Also, a male martin may copulate with a compliant female when spouses' backs are turned. He may father more offspring by doing so and her brood will have greater genetic diversity. But infidelity is a two-edged sword: all of the youngsters he nurtures so devotedly in the nest at home, may not be his — 'what goes around comes around'!
There's a price to be paid for security. Songbirds, such as robins and blackbirds, generally make 'cup' nests, from which chicks can observe, and discover, the world around them. Pity the poor martin youngster emerging for the first time from darkness into light, 'cast into this breathing world, scarce half made up' etc. After three weeks in warm womb-like security, it must now sink or swim.
The name 'martin' dates back to the medieval bestiaries and animal fables; this is a popular bird. "The martin and the swallow are God Almighty's birds to hallow".
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Birds of Ireland: Swallow