Why do birds leave Britain in autumn and winter?

The advantages of going south are obvious, particularly for insectivorous birds. Swallows and nightingales would be taking a big chance to risk a British winter, when just a few very cold days could be enough to starve them to death. Further south there is more food all year round, but there is also much more competition. Not only are there African resident birds, but also migrants from Europe and Asia. A patch of scrubby African forest is quite a melting pot of nationalities between October and March.

Wherever they end up, there is no doubt that their immediate surroundings will look considerably different to the frigid, bare British countryside in winter.

In Spain or North Africa, migrants will forage among olive leaves and evergreen scrub. Willow warblers in tropical Africa feed in the crowns of acacia trees on lush savannah, where only giraffes can reach. Cuckoos will disappear into dense forests, while garden warblers will head into thick montane scrub with a biodiversity many times higher than ours.

Northern wheatears swap moorland for semi-desert landscapes, and nightingales will sometimes throw off the reticence they show in the UK and feed in gardens and patches of cultivated land in Africa.

Do birds change their behaviour when they migrate?

Much as ‘our’ birds find themselves in a changed landscape, they do not become fundamentally different. A spotted flycatcher in tropical Africa does what a spotted flycatcher does in Britain: it makes darting sallies to catch insects in flight. It might catch termites and other exotic invertebrates, but its feeding methods are much the same.

Arctic terns dive for fish, turtle doves eat grain on the ground and reed warblers climb up and down stems of marshland plants with their strong feet, just as they do every day of their lives in the UK.

If anything, it is our resident birds that change diet the most when our migrants leave these shores; blue tits and many others switch from feeding on caterpillars and other insects to a diet of seeds and nuts.

How long does it take birds to migrate?

It’s easy to forget that our migrants don’t just wake up one morning under African skies. Most take a month or more to get to their wintering grounds, and they must adapt to any places they pass on their travels, as well as their destination. They need to overfly the English Channel and the Mediterranean, then the Sahara Desert. Settling into the African bush must be easy by comparison.

Different types of summer visitors

Osprey

The osprey’s practice of hunting fish by plunging into water from a height is easily translatable from Britain to West Africa, where our birds winter. The practice also works equally well in salt water as in fresh. Five thousand kilometres away, our birds mainly stay on the coast in winter, fishing in the shallow, sheltered water just offshore, or along large rivers. They compete with African fish eagles in some areas.

In Britain, ospreys arrive in March and April to inhabit freshwater lakes, mainly in Scotland. They’re also found at Rutland Water, in the midlands, and in Poole Harbour, Dorset.

Wheatear

The wheatear is mostly a bird of cropped grassland and moorland, commonest by far in northern Britain. In October it departs for Africa, with European birds spreading across from west to east just south of the Sahara. They settle in distinctly arid areas, often at altitude, with rocky outcrops, where they keep a territory and defend it aggressively from other birds. They feed on invertebrates in the same way everywhere, perching on a rock or bush-top to survey the scene, then running or flying after their prey.

Chiffchaff

Migrant chiffchaffs leaving these islands can winter anywhere between Spain and tropical West Africa, with the bulk settling around Senegal, just south of the Sahara. They live in a wide variety of scrubby areas, often in arid regions – rather a different profile from the tall, lush deciduous woodland that is their typical British breeding habitat. Chiffchaffs use the same foraging methods, restlessly searching the leaves for small invertebrates. They leave their wintering grounds in February and arrive back here in March. The chiffchaff is widespread, breeding in woods throughout Britain.

Yellow wagtail

This buttery-yellow delight is a much-declining bird of meadows, wetlands and arable farmland. One of the best ways to see it is at the feet of horses and cattle, feeding on the flies disturbed by hooves. Translate that to Africa, and you can add in zebras and elephants. The yellow wagtail winters across tropical Africa, but most of our birds are in the west. They feed in much the same way everywhere, dashing after invertebrates on the ground, or darting into the air. In Britain, they’re found mainly in central and eastern England, from April to September.

Redstart

In Britain, this delightful robin-like bird is strongly attached to the sessile oak woods of the north and west with their tangles of lichen and moss, dripping with insect life all summer long. Perhaps surprisingly, it swaps this lavish habitat with much drier, scrubby habitats in the Sahel of West Africa, even in Mali, much of which is desert. In Africa, it probably spends more time feeding on the ground, like a robin.

Common in much of Britain, you can find redstarts in the New Forest, Central Wales and the Lake District, as well as much of Scotland.

Swallow

The swallow has one of the longest migrations of any bird, with the British population heading for the eastern part of South Africa, where they arrive in November as harbingers of spring. They feed there in much the same way, swooping low to catch juicy flying insects, although they also nab some seeds from Acacia cyclops, hovering at the tips of the branches. They also roost in huge numbers in reed beds.

Swift

Swifts arrive in Britain in late April or early May, and are a welcome sight and sound in the skies. However, they don’t stick around here long – staying just long enough to breed before beginning their autumn migration back to Africa in late July or early August. It’s believed that their autumn migration is prompted by fewer insects in the air.

Turtle dove

It’s quite unusual for a seed-eating bird to be a long-distance migrant, but the turtle dove breaks the rule, leaving in September to fly to the Sahel region, a dry, scrubby belt south of the Sahara, in countries such as Mali and Senegal. Here it is much more arid that in the farmland of Britain, although the turtle dove simply feeds on seeds and grains, as it does here. Now rare in Britain after a drastic decline, the turtle dove occurs principally in South East England. Look for it in summer at the Knepp Estate in West Sussex, Martin Down in Hampshire, and much of East Anglia, such as RSPB Fowlmere, Cambridgeshire.

Cuckoo

Tracking of cuckoos in recent years has revealed much about their extraordinary migration. Many adults leave Britain on their southward journey as early as June. They then fly to West Africa (Nigeria for example), followed by a journey into the deep rainforest of the Congo Basin – a minimum of 6,500km –where they spend most of the winter. This is a completely different habitat to the marshes, moors and farmland they inhabit in Britain, and they are hardly ever seen in the rainforest.

The cuckoo returns to Britain in April. Following a big population decline in the south of England, they are now most common in northern England and Scotland.

Blackcap

This common warbler is a short-range migrant that winters in southern Spain and Morocco. But in recent years, breeders from Germany and Austria have been flying west to spend the winter with us in Britain, and these birds often visit garden feeders.

Atlantic puffin

What puffins did in winter was a mystery until recently. By tagging these tough little members of the auk family with geolocators, scientists have shown that they head far out to sea, braving several months in the stormy North Atlantic.

Whitethroat

In the weeks before it migrates, this hedgerow warbler switches from insects to sugary berries to rapidly put on weight as fuel. It spends the winter in the arid, scrubby region known as the Sahel, to the south of the Sahara.

Arctic tern

Nicknamed ‘sea swallows’, these graceful, long-winged seabirds are true globetrotters. They swap our northern winter for the permanent daylight of the Antarctic summer, looping around the Atlantic Ocean to get there in an epic journey up to 35,000km long.

Little tern

The little tern is one of the UK’s smallest seabirds and weights only 40-6og. They spend the winter in Africa, and return to the UK in April to nest on our sandy and pebble beaches.  Their nests are vulnerable to predation, and to disturbance by humans and dogs. If disturbed, adults will leave the nest, leaving their eggs or chicks exposed to the cold and predators. Little tern nesting colonies are also struggling with climate change, and rising seas and coastal flooding can wash away nests and chicks. Their return migration takes place in August and September.

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Words: Ben Hoare, Dominic Couzens, and Megan Shersby.

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