Wood Warbler (Phylloscopus sibilatrix)
It seems highly odd that a bird living in mature woodland should practise anything as ostentatious as a song-flight, since presumably the bird’s space for such aerobatics would be rather limited. Nonetheless this is exactly what the Wood Warbler does, following a horizontal course from perch to perch while flying with fast but shallow wing-beats. The song is uttered either just before or just after becoming airborne, and carries on until the bird lands. The song itself consists of two parts which may be uttered independently of one another. One is an accelerating, shivering trill that sounds like a spinning coin coming to rest, and the other is a series of mournful piping notes – the two could hardly be more different.
Having made all these efforts male Wood Warblers don’t always settle for a single mate. Depending on the location and, evidently, upon the year, up to 40% of the population may acquire two mates instead, hogging the available talent and leaving some competitors unpaired. This tends to happen when a male has acquired a mate and she is incubating; finding itself independent and not especially busy, such a male willingly solicits for another mate, either on the edge of its territory or, sometimes, by moving to a different one. If he is successful, he will then give the lion’s share of his attention to either the primary or secondary mate, helping to feed and tend the chicks, although occasionally the females may bring their respective offspring towards the rival’s nest and the male divides his attention.
The Wood Warbler must fit all its arrangements into a short breeding season. Having arrived towards the end of April, these birds are early returnees to their wintering grounds in Central and East Africa, with the main departure occurring in August.