The astonishing power of birds to fly huge distances can be seen occasionally when migration goes wrong. Each year, a few wandering individuals from Asia’s migratory bird population arrive in Britain, having lost their way or been blown astray by storms.
The migration journey of birds has many hazards, especially for small species. Migrating birds are at the mercy of the weather until they reach their destination. Heavy rain may quickly drench them and force them to the ground or into the sea, and strong winds may blow them a thousand miles or more off course. Pipits, warblers, and thrushes are just some of the many rare birds who fly from Asia.
Clouds may blot out the sun or stars, by which most birds navigate, causing them to fly for several days or nights on end in the wrong direction. These migration hazards are usually responsible for the appearance in Britain of species that normally breed and winter on the other side of the world, in Asia.
Vagrants vs. Rarities
Technically, a vagrant or accidental is defined in Britain as a bird recorded less than 20 times. Several Asian species occur slightly more frequently than this in Britain, and these cannot be described as vagrants but rarities. Fantastic ornithological skills and knowledge are sometimes needed to spot and identify birds of either category from Asia.
Where Do Asian Migrant Birds Come From?
By definition, Asia begins at the Urals, a long mountain range running from north to south and marking the eastern limit of Europe, over 4000km (2500 miles) east of Britain. Its northern parts are occupied almost entirely by Siberia, which stretches for some 6500km (4000 miles) eastwards to the Bering Straits. At its eastern end, Siberia’s neighbors are China, Mongolia, Korea, Japan, and Alaska.
Only a handful of bird species from Asia migrate purposely to or through the British Isles: the main examples are knot, whitefronted geese, and curlew sandpipers. Most of Asia’s migratory birds spend the breeding season in Siberia or its eastern neighbor countries and winter in southern Asia, Australasia, or Africa.
Nevertheless, wind-blown or disorientated individuals regularly arrive here, thousands of miles off course, with no hope of reaching their normal wintering grounds or rejoining the rest of their species. Generally, most of these Asian birds occur in spring or autumn, during periods of strong easterly winds. They tend to occur on the east coast of Britain.
Pipits are one of our commonest Asian visitors. In Britain, rock, tree, and meadow pipits are common breeders, and in Europe, tawny and red-throated pipits also occur. Three other species breed only in Asia: Richard’s, Pechora, and olive-backed pipits, and of these, Richard’s pipits occur in Britain most often, over one hundred being seen some autumns.
They are large, boldly streaked birds, reminiscent of skylarks in color and habits, but their loud call is unmistakable.
Several Asian warblers are also recorded in Britain, providing some of the greatest identification problems. Attention to detail is always essential, and notes on the spot are invaluable if identification is to be made.
Yellow-browed warblers, looking like a cross between a firecrest and a willow warbler, can easily be overlooked. These birds are tiny, only 10cm (4in) long, with two pale wing bars and a long creamy stripe over the eye. Much less seen is Pallas’s warbler (or Pallas’s leaf warbler).
This species breeds from Siberia to the Sea of Okhotsk (north of Japan), yet at least one or two occur in Britain each October or November. It is only 9cm (3in) long and weighs only 5g (1oz).
Both these warblers—and the dusky warbler, another Asian species—are related to the willow warbler and chiffchaff, but other warbler groups also have Asian representatives. The lanceolated warbler, a close relative of the grasshopper warbler, is rarely seen in this country. It is exceptionally skulking and can be seen running like a mouse along the furrows of a field rather than flying in full view.
Of the Hippolais warblers, the booted warbler is a great Asian example. Like the previous species, there have only been a handful of records in Britain, all in autumn. The paddyfield warbler, a relative of the reed warbler, is another example.
Several species of thrush breed beyond the Urals, and these are occasionally recorded in Britain. The Siberian, eyebrowed, and dusky thrushes have been recorded a few times each, but the black-throated thrush is now becoming more popular. This beautiful bird is the size of the song thrush but with grey upperparts, white underparts, and black face, throat, and breast.
White’s thrush is even more frequent, which is larger than the mistle thrush and is characterized by golden-brown plumage with black crescent-shaped markings and striking black and white bands beneath the wings.
Some Asiatic bird species that occur as vagrants in Britain do not automatically qualify as Asian vagrants simply because they breed in Eastern Europe and Asia. Of the waders, the sociable plover, a lapwing-like bird, is a typical example of this.
In contrast, the sharp-tailed sandpiper, rather more like a dunlin, breeds only in north-east Siberia, 8000km (5000 miles) away, yet many have been identified here. Others, like the lesser golden plover, also breed in North America.