Icterine Warbler

The key characteristic of Icterine Warbler song that instantly separates it from anything else is its timbre. Icterine has a peculiar 'squeaky toy' timbre, due to a very rich presence of harmonics. This is most audible in the longer notes, but looking at sonagrams, more than half of the notes in the song show great piles of harmonics. Not even its closest relative Melodious Warbler has a similar degree of 'squeakiness'. There are other ways to separate the two species, which are described under Melodious, but timbre is a good place to start. Icterine may have a few whistled notes too that lack the squeaky toy timbre, typically associated with wild twists and turns of pitch, but far more of the song has it than lacks it.

Icterine Warbler song exists in two main structural variants, which may appear in the same bout of singing. In the commonest variant, the strophes are relatively short (mean 7 s, n = 8 individuals) and contain a succession of motifs, each one repeated several times, sometimes with slight variations in rhythm. A motif may consist of a single unit of sound, an imitation in most cases, or two combined into a rhythmic pattern. Sometimes a previous motif is interjected now and then between iterations of a new one. When Magnus analysed songs of 8 individuals he found that a new motif was introduced to the strophe on average once every 1.1 seconds. In those 8 individuals, the mean varied from 0.6 to 1.5 s. This is a rate of variation very similar to a Eurasian Reed Warbler, although Icterine's song seems far more varied to our ears, because the kinds of sounds used are much more contrasting. Usually there are longer series of repetitions in the first part of each strophe, and towards the end the new motifs appear in slightly quicker succession.