Pound for pound, swallows might be the greatest migrants in the skies. Every February they gather in the flea-infested reed swamps of South Africa and feed themselves up to a still-puny 24g, before heading 6,000 miles north to Europe. When they cross Zambia they're revered as Nyankalema (the bird that never tires), and when they reach Nigeria - after darting through the foaming rapids of the Congo, apparently just for fun - their resilience is deployed in witchcraft recipes. Fried sparrow makes you indestructible. And to get across the Sahara, the hardy little blighters have to fly nonstop for up to 16 hours a day, to reach, finally, a warm welcome in Europe, not just as the heralds of summer but as the birds that plucked the thorns from Jesus's brow.

Some of these heroic creatures choose to roost in south Wales, specifically in Horatio Clare's barn - at the farm that was the backdrop to Running for the Hills, his bestselling memoir of his 1970s childhood. One day, watching a flock preparing for their return leg, Clare resolved to follow their northbound commute the next spring. A Single Swallow is the tale of that journey.

Clare has produced an enthusiastic, often elegiac, chronicle of his encounters with the swallows on his travels up the western half of Africa, watching them gathering in their “biblical plagues” in Bloemfontein, perching on phone lines along battered Zambian bush roads and cavorting over the kasbah walls in Algiers and the rooftops of Marrakesh. The birds serve him well, both as intriguing natural wonders and as a fitting metaphor for the uneasy accommodation between men and ecosystems in Africa.

Sadly, though, that's not all he has written. If his book had been adequately edited and printed at half the length, the result would have been a slim travelogue to match the relatively slight pretext and the swiftness of the journey involved - Clare scorches from Cape Town to Casablanca in just eight weeks. Instead, his experiences have been overstretched, with no detail too insignificant, no encounter too inconsequential. Ants nibble his sandwich in Namibia, and he lets us know; later that day, a millipede crosses the street, and we're there to watch; an IT consultant in Morocco tells a story about a mainframe server he once saw in Russia, and we get to listen in.

The overall effect is as unfocused and indulgent as a gap-year diary, and just as infuriating. A Single Swallow took its maiden flight across my living room at the point where its author, inspired by a hotel bookshelf, delivers a short seminar on the plot devices of the pulp-thriller writer Wilbur Smith; it was airborne once again during the retelling of a drunken backpackers' night out in Namibia, when Clare hears a soft-rock classic on the jukebox and muses: “I could not help but look around and ask, What if God was one of us?”

In sections, the travel merits the attention to detail (CongoBrazzaville and Cameroon are full of human warmth, bureaucratic comedy and perilous terrain), and every time the swallows reappear, a sense of purpose returns. But by the time we've reached Gibraltar (at which point Clare, suffering some sort of nervous collapse, throws all his notebooks into the sea), and have been hectored about the existence of God, the geopolitics of hotel-room television and the psychology of corporate loyalty cards, the tiny, dauntless birds have all but slipped from view. The lingering image is of a talented young writer - guilty of exuberance shading into overconfidence - being left to twist in the wind by editors unwilling to rein in his text.

A Single Swallow by Horatio Clare
Chatto £17.99 pp336

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