It’s difficult to think of the familiar house martin as a mystery bird, but it is. Every autumn the entire European population of some 12 million, together with an estimated 78 million from Russia and Asia, heads south into Africa. Where they go after that remains a puzzle, for unlike their close cousin the swallow, whose migration routes and wintering areas are well known, they disappear when they get to the Dark Continent.

Birdwatchers in eastern and southern Africa do see a few but they are heavily outnumbered by swallows. Current opinion suggests that they may be widespread throughout southern Africa but simply stay too high in the sky to be seen from the ground even with binoculars.

Though both swallows and martins feed on flying insects, the former are low-level feeders and the latter fly much higher, so they don’t compete with each other. Many people find them difficult to tell apart but there’s no real problem if you get a good view: the house martin has a distinctive white rump; the swallow has the deeply forked tail.

It is impossible to provide food in your garden for either species but both will readily adopt suitably sited nest boxes. House martins build cuplike mud nests under eaves, often in villages or in the outer suburbs, and like to nest in loose colonies. If there’s a colony near you, then it’s worth trying to attract them. Swallows are country birds nesting in barns, stables or even garages. They build an open nest, usually on rafters. Erect suitable artificial nests and you may well attract them.

The natural nests of both species often fall down during spells of dry weather. This doesn’t happen with artificial nests so if you provide them with nest boxes you will be helping two remarkable species that are under increasing pressure in the 21st century.