Another summer visitor with a somewhat nondescript appearance but a distinctive call - I've seen it accurately described as a "wistfully descending cadence". In late summer these birds, (including juveniles only a few months old), travel 5,000 miles to spend the winter in Sub-Saharan Africa. Swallows fly even further, to South Africa. Prior to name standardisation in 1843, the Willow Warbler was sometimes called the "Willow Wren". They are unusual in that they moult all their feathers twice a year: once at their breeding ground, then again at their wintering grounds. We don't know why.