A Single Swallow, By Horatio Clare<br/>Say Goodbye to the Cuckoo, By Michael McCarthy

If migrant birds could talk, what tales they could tell - though the late Miriam Rothschild insisted they would only complain about their parasites. Cuckoos and swallows are the true heralds of summer. The swallow arrives, scything through the air, belly-dipping over the grass, often during the first truly warm days of the year. The cuckoo is more of a "wandering voice", often heard, less often seen; its appearance used to be announced on The Times letters page. Both birds excite and uplift us with their promise of easy-living summer days.

These two books are both journeys in search of a migrant bird, but there the resemblances cease. Horatio Clare traces the swallow's epic spring migration from Cape Town to his barn in Wales as a kind of rite-of-passage, roughing his way through Africa and Europe. He travels at bird-speed, doing his best to follow the swallows as they stream ever northwards, over dried-up rivers, jungles, deserts and olive groves.

Michael McCarthy's journey is more inward. He spends time with experts in various locations, discovering the ways of our summer migrants and finding reasons why we should care if the likes of the cuckoo are heard no more in the land. The title sounds like an elegy, but the tone, until near the end, is upbeat and celebratory.

Clare grew up with the ritual arrivals and departures of swallows in the family barn in South Wales (whose view of the distant hills reminds him of Africa). A keen birdwatcher, he planned the expedition imagining the migration of the swallow as "a vast wind-tunnel hurtling diagonally up the globe". The trouble is that swallows do not migrate in a single electric-blue swarm, nor do they all take the same route. Following them in any meaningful way is impossible (they have evaded satellite tracking), even without the realities of African travel. Bureaucratic and military hurdles ruled out large chunks of the direct journey, including the crossing of the Sahara, the least known part of the swallow's life.

Clare got off to a rollicking start in South Africa, with the swallows limbering up for the race, "entire dark whirlwinds funneling down into the reeds" which "shook and rattled, amplifying the rustling of wings". Thereafter, as the author toils his way north through Namibia, Zambia, Congo-Brazzaville and Cameroon by hire-car, bus, motorbike, canoe or on his blistering feet, his encounters with swallows are briefer – on power lines, streaming upriver, "whipping in swirling dives", and at a desolate railway station in Cameroon, their "blue backs shining in the hazy sunlight like hardened silk".

Along the way, he picks up snippets of local lore. In South Africa the birds are inkonjami, "the bird that brings the rain". In Zambia they are nyankalema, "the bird that never gets tired". In Niger, where an unreported war prevents his going further, the swallow is giri-giri and used in witchcraft; eviscerated and boiled to a paste, it protects you from traffic accidents and plane crashes. To be hung over in the Pyrenees is to "have eyes like swallow's balls".

Swallows, it seems, are a strange mixture of toughness and fragility. Despite weighing "little more than a full fountain pen", they beat their wings 240 times a minute and travel at up to 14 metres a second. When their body fats are used up, they can derive emergency nourishment from their own muscle and organs. The effort kills three-quarters of them before the equivalent of their teens.

Real swallows are more the focus than the subject of Clare's odyssey. The "single swallow" is the author himself, a self-confessed romantic who throws himself into life on the road with youthful exuberance and writes with an easy lyricism and in vivid detail.

This writer wants us to share everything. Try this: "We laughed and puffed and squeaked in protest as we were pawed and wrestled, seized and danced with, pointed at and laughed into the bar, then out of it". It's immediate and in-your-face, but after a bit I too was squeaking in protest. Too many verbs, too much action.

Say Goodbye to the Cuckoo is a quieter book, at once a celebration of our feathered spring-bringers and an elegy to the loss of once-familiar sights and sounds. Less than one in ten of those McCarthy asked had ever heard a nightingale. He touches on the place of migrant song birds in our culture, from the Song of Solomon to that fictional nightingale in Berkeley Square. He tells the story of the discovery of our migrant birds, so much of which is surprisingly recent. A century ago, no one knew where the swallows went in winter. He does it with a light touch and wide-open eyes.

McCarthy is a journalist with the beguiling knack of getting people to talk about what interests them with simplicity and passion. He goes birding with the likes of Mark Cocker (who understands sedge warbler-ese), Angela Turner, whose classic book on the swallow sent Horatio Clare on his way, and Nick Davies, who summons cuckoos by whistling through his thumbs.

McCarthy knows enough to know what to ask them, and his sense of awe and wonder at what he discovers is palpable. Migrant song birds have everything – class, attitude, beauty, mystery, the lot.

Are we sliding towards another silent spring? Is it really goodbye to the cuckoo? Their numbers are falling at a worrying rate: there are fewer than half the cuckoos that we had in 1967, a third fewer again since 1994. We know the stats, more or less, but we don't know why; maybe too many are being shot on passage, or it might be something to do with a parallel decline in the cuckoo's favourite food – big, hairy caterpillars.

What would it be like to be the first generation in history to witness spring without the cuckoo (or the nightingale or the turtle dove)? A hurt, a defeat, even bereavement for some, though perhaps nothing very much to most of us. But, McCarthy suggests, it is more fundamental than that: "The cuckoo had always come back. It wasn't only part of the spring: it was the eternal cycle of death and rebirth." Without the cuckoo's wandering voice to welcome in the spring, how are we going to feel about ourselves?

Peter Marren's books include 'The New Naturalists' (Collins)

The meaning of seasonal migration

The most common migration involves flying north to breed in Arctic summer (making full use of the long days ) and returning to warmer regions in the south when the days shorten. The reward for diurnal birds that make this ogruelling seasonal trip along 'flyways' (routes that follow mountain ranges or coastlines) with a constant threat of predation, is a larger clutch of eggs than those of non-migratory species. Migratory routes such as that of the cuckoo (left) are either genetically programmed or learned.