The Willow Warbler (Phylloscopus trochilus)
is strongly migratory, with almost all of the vast population wintering in sub-Saharan Africa.
One of the most numerous birds in Europe, more than a million ringed birds, by 2004, resulted in 2500 retraps or recoveries, representing a substantial database that gave ornithologists valuable information into the migration routes taken by this tiny bird and their habits during migration. These night migrants travel furthest from Siberia to Southern Africa… a one-way trip of 14000 kms! For a bird weighing less than 12g, this is a remarkable feat. They are capable of fast refueling and during their day-time stops recharge their energy levels. If faced by obstacles like the Sahara desert, they have enough in reserve to cross such a hurdle in three or four nights, resting up during daytime.
Willow warblers are one species that show a reaction to climate change with both their arrival and departure in and from Europe having shifted by a week at either end of the season so that their stay has become shorter by two weeks in sub-Saharan Africa during the 40 years that they have been monitored. Effectively the Sahara is growing rapidly southwards causing the barrier that needs to be crossed to stretch the bird to a point where they fail to cross back to Europe. Some bird populations have declined by 30%.
The Willow Warbler is almost unique amongst birds in that it moults all of its feathers twice in a year, on the breeding grounds and again on the wintering grounds; the reason for this have to do with the length of the migration.
They are insectivores. Typical lifespan is two years but birds in excess of 10 years have been recorded.
The ID features are:
- distinct pale yellow eyebrow and underparts
- tail notched
- legs pink
- distinct yellow under-wing, sometimes visible on the shoulder when the wing is closed.
In South Africa it usually is a solitary feeder, but sometimes it joins mixed bird parties. Forages by restlessly gleaning off leaves and branches in middle and upper strata of trees and bushes, much like white-eyes... a tough subject to photograph!