To Timbuktu and back - More than two billion songbirds migrate from Europe to Africa each autumn and then back again in the spring.
Why bother? - Migration allows birds to chase the seasons and exploit favourable conditions for breeding and feeding.
Way to go - Most of our migrants come to the British Isles via the Y-shaped ‘East Atlantic Flyway’ – a zone linking a wide swath of the Arctic from Canada to Russian Siberia with Central and Southern Africa.
Rising to the occasion - Not all birds migrate by heading north or south. Skylark, snow bunting and kingfisher are altitudinal migrants, travelling from lower altitudes to higher altitudes and back. They don’t clock up big miles, but they do have to adapt to very different living conditions.
Different strokes - While some birds migrate to us to breed in summer, others migrate to our shores in winter to escape harsh northern weather. Then there are those species that partially migrate - like starlings, chaffinches, lapwing and curlew - where our breeding birds are joined by others from the continent.
Fly me to the moon - The longest migration of any bird is that of the Arctic tern. Some migrate every year from the Arctic to the Antarctic - that’s over 55,000 miles a year. For a bird that can live for over thirty years, that adds up to a staggering total distance travelled, equivalent to three times to the moon and back.
Small wonder - One of our smallest African migrants is the willow warbler. Weighing in at a mere 12g, this tiny bird crosses deserts, seas and mountains on an epic journey of some 8,000km every spring – before making the return journey after breeding.
Highflyer - Whooper swans join us for the winter from Iceland and are some of the highest-flying migrants. Airline pilots have clocked them at 8,850m. They travel at around 55mph and reach the UK in a single twelve-hour flight.
Packed lunch or service station? - Some birds take their energy supply with them in the form of fat reserves. Others use stopovers to rest up and refuel before moving on. Some long-distance migrants do both.
Birds of a feather - A less well-known form of migration is when birds move to moult. In early summer male goosander head to Norway to hang out in safety and change their plumage. Shelduck exhibit similar behaviour, heading to places such as the Severn Estuary and the Wadden Sea in late summer.
Taking a chance - The first year of a songbird’s life is the most hazardous with 80% of deaths thought to occur during migration. If they survive their maiden trip, however, their chances of survival are better than if they didn’t migrate at all.
The heat is on - In addition to finding food and avoiding bad weather, one of the biggest challenges to migrating birds is overheating. Flight muscles can exceed 44˚C and when they do a bird can’t fly anymore – a big problem if you’re over open water or a desert.
The mystery is history - Before bird ringing, radar, GPS and satellite tracking technology, nobody knew why some birds disappeared for winter. Once it was thought swallows hibernated in the mud at the bottom of ponds and barnacle geese became goose barnacles. Then in 1882 a stork turned up in Germany with an African spear stuck in it – and the penny dropped.
Put a ring on it - Much of our understanding of bird migration comes from ringing schemes where metal rings bearing unique identification numbers are attached to a bird’s leg. This started back in 1909 and has been continuing ever since.
Go west - Traditionally it was thought blackcaps migrated to Africa. In the 1970’s this was questioned when more and more birds seemed to stay on in our gardens. Evidence from bird rings then revealed that these wintering birds are not the same ones that were singing from your garden hedge in the spring and had migrated west from the continent. Warmer winters and plentiful food are the reason this strategy works.
Heavy fuel - Many migrant perching birds, such as whitethroat, blackcap and ring ouzel, are predominantly insectivores during their stay with us, feasting on protein-rich bird building materials for eggs, chicks and feathers. After breeding they switch to energy-packed seeds and fruit to lay down fat and fuel their migratory flight south.
Sense of direction - Landmarks, smell, learning, inherited knowledge and Earth’s magnetic field and are various ways birds navigate around the world. If a homing pigeon loses its sense of smell, its sense of direction disappears too.
Follow your nose - or your eyes - Small quantities of a magnetic mineral called magnetite have been found in the beaks of pigeons and other birds. It’s thought to be linked to an innate ability to navigate using the earth’s magnetic field. Some birds have a specialised protein in their eyes called Cry4 which may enable them to ‘see’ magnetic fields.
Travelling light - A less obvious part of preparation for migration is the shrinking of birds’ reproductive organs and livers. Their cell metabolism also changes, allowing them to burn fat and use oxygen more efficiently.
Pump it up - The heart rate of flying birds can increase by over 400%. This helps pump oxygenated blood to the flight muscles more efficiently.
Food miles - Some of our birds of prey are migrants, moving south for the winter. Honey buzzards need wasps, bees, and other insects to feed on. Ospreys seek out better fishing where the water doesn’t freeze. Hobbies follow their food – the swallows and martins that are also migrating.