Colours of Wildlife: Willow Warbler
Created | Updated Jan 7, 2018
Willow Warbler
Willem is a wildlife artist based in South Africa. He says "My aim is simply to express the beauty and wonder that is in Nature, and to heighten people's appreciation of plants, animals and the wilderness. Not everything I paint is African! Though I've never been there, I'm also fascinated by Asia and I've done paintings of Asian rhinos and birds as well. I may in future do some of European, Australian and American species too. I'm fascinated by wild things from all over the world! I mainly paint in watercolours. . . but actually many media including 'digital' paintings with the computer!"
Today I have for you a dainty little bird! This is a Willow Warbler, Phylloscopus trochilus. The scientific name means 'leaf-seeking wren', and it used to be called a 'willow wren', though today it is not considered a close relative of wrens, instead being a member of the warbler family proper. It is not a spectacular bird, being tiny (only about 12.5 cm/5" long at most), and is coloured in dull brownish, greenish and yellowish tones. Yet, it is one of the most amazing birds in the world, if you consider what it actually does.
Ultramarathon Fliers
The field of bird migration is one which we're just beginning to research, and it is in this field that the willow warbler shines. These tiny little birds, half or less the size of a sparrow, yearly complete one of the longest migrations of any bird species. Willow warblers occur in large numbers in central to northern Europe and northern to north-eastern Asia, which is where they breed. They prefer open, low and scrubby woodland and forest in those regions, where they methodically search trees, bushes and patches of lichens or moss for small insects. They feed, and breed, during the summer, and can reach great densities, with substantial populations especially in the Scandinavian countries and in Russia. But come the northern hemisphere winter, food sources dry up, and cover is lost as trees and shrubs shed their leaves. Then the entire huge population of willow warblers (about a billion birds) take to their little wings, and move south towards more equable climes. That means Africa. Just about all the willow warblers in all of Europe and Asia come for a yearly vacation in sub-Saharan Africa.
Willow warbler wintering grounds aren't all actually experiencing summer at the time: perhaps half of the willow warblers move to Africa north of the equator, though south of the Sahara, which region technically also experiences winter at the same time as Europe and Asia (though winter in north-tropical Africa doesn't really count as winter by European standards). But the other more-or-less half does move to south of the equator, where it is summer while winter lasts in the north. These are the ones covering the greatest distances. It has been found that those birds in the extreme north-eastern parts of the range, eastern Siberia, actually fly all the way down to South Africa. This can involve flying a distance of 12 000 to 13 000 km/7 500 to 8125 miles! This compares well with the migration distances of other avian marathoners like terns, sandpipers and godwits. But willow warblers are much smaller than those birds, and don't have comparatively long wings, as the similarly small, long-distance-flying barn swallows do.
We don't yet know how these tiny birds do it. Recently we've been using electronic trackers and satellite data to follow the migrations of larger birds like cuckoos and godwits. This enabled us to see exactly which routes the birds follow and the time they take to cover certain distances. This has provided amazing info showing that these birds often fly non-stop for thousands of kilometres at a stretch. But we haven't yet done this for the very small birds like willow warblers. We do know, by having put rings/bands on birds and then recapturing them, that they do fly these amazing distances, and we have a rough idea of the routes they take, but we don't yet have the exact details. They probably don't fly most of the way in single, uninterrupted flights; they likely need to stop and refuel several times during the journey.
European-Asian Africans
Still it is interesting to think that these familiar and common European and Asian birds are just as much African. Willow warblers arrive here in South Africa in spring, and make themselves known by their soft, two-syllable 'too-wheet' contact calls, and by their modest but sweet little warbled songs. In the hot seasons they are the most numerous warblers in the country, ranging almost throughout the whole of it, wherever there are trees and shrubs. They're only absent from moist, dense forests, and from treeless grassland and desert. They're quite frequent in thorny savannah, and the one in the painting you can see perched on the branch of a thorn tree. Willow warblers have also adapted well to suburban gardens. They frequently partner up with other bird species in mixed hunting parties, where each species targets a specific kind of insect in a specific part of the vegetation, so that a critter that escapes from one can get grabbed by another.
In South Africa we actually get a mix of willow warbler 'races' (for want of a better word) coming from disparate regions and differing slightly in appearance. Some are more yellow, some are more dull-brown or greyish, and some are intermediate. The east-Asian ones are the greyest; the western-European ones are the yellowest. All of them mix it up down here, with the birds from Finland and Sweden being the commonest. When seen, they can be confused with the somewhat larger Icterine Warbler, and the significantly larger Olive Tree Warbler, but as soon as they open their mouths and call, they give themselves away. Here is a photo which already appeared in this column, showing an icterine warbler (on the left, the larger bird) as well as a willow warbler, captured during a ringing operation. Compared side by side the size difference is clear to see, but when you see a single, distant bird in a bush or tree, it's not always easy to estimate just how big it is. The icterine and olive-tree warbler both have longer, stouter bills, and both are much rarer birds, and mostly quiet during their South African stay.
At present, willow warblers are abundant, despite having experienced declines in some parts of their breeding range. Close relatives of the willow warbler include the Chiffchaff, Western Bonelli's Warbler and the Wood Warbler, all of which migrate to Africa north of the equator. Six additional members of the same genus, called woodland warblers, are non-migrating species that only occur in Africa, in woodlands or in forests. None are at present considered threatened.
