Two very common species, but still a classical identification issue even for experienced birders !
- Structure of the song and differences with Mediterranean warblers :
Both species have a rich whistling song including an astonishing variety of notes. While typical songs are quite easy to identify, the main confusion is caused by subsongs produced by both species. Hence, the challenge is to find keys to identify sub-singers.
A first look at the structure of the sound shows that those warbling songs are unique among European birds, so that there should not be too many species to rule out when listening to a presumed Blackcap/Garden warbler . The song is relatively slower than Mediterranean warblers : it is fluid and does not include clicking sounds or rattles between the whistling notes (while Mediterranean warblers do). Keeping in mind this “singing, whistled” structure, it should not be difficult to rule out any other warbler.
Another example of Mediterranean warbler : Subalpine warbler (Sylvia cantillans iberiae). Notice the numerous “tek” clicking calls repeated between the whistled notes, and the “fast, messy” structure of the song :
2. Ruling out Common whitethroat (Sylvia communis)
A confusion with Common whitethroat (Sylvia communis) should be avoided : The latter includes typical raspy notes (“Tchèrr”) and usually produces shorter phrases :
- Even odd singers always feature raspy sounds (Tcherr) and never produce true whistles.
- Simple structure with many repetitions
- The notes are thicker (broad bands on sonogramms) than in Blackcap/Garden warbler.
This common whitethroat produces an interesting variety of songs, but all of them are short and include very raspy notes, a bit like a Skylark (Alauda arvensis) (not whistled) :
3. Identification of Blackcap (Sylvia atricapilla) :
Blackcap produces a whistling sound, that is particularly rich for a warbler. It often includes “diagnostic” flutey notes towards the end. The full song is typical and quite easy to identify, but many birds just emit “subsongs” (especially in early spring) that don’t feature the most classical notes. Let’s listen to a typical song :
And then to a typical “subsong” :
In any case, note that :
- The notes are very clear (usually clearer towards the end of the song), and gently curved (a lot of downcurved whistling notes)
- The phrases are usually long, as is the gap between two phrases. Hence the blackcap sounds more “relaxed” than Garden warbler does
- The structure of the phrase changes between the beginning and the end of the song : The typical song begins with short, highly modulated notes and ends ups with thick, longer whistling notes around 2.5-3kHz
- General frequency between 2 and 5 kHz with a 2-4kHz ending
- A melodious warble, with about 6 notes/second or less
- Very “blackcap” notes to look for seem to be steep short descending note (“chiew”) among more horizontal modulated notes (“waves” that correspond to Robin-like thin whistling sounds) . Even sub-singers repeatedly produce these notes :
4. Identification of Garden warbler (Sylvia borin) :
Garden warbler has a more squeaky song than Blackcap, never including very flutey notes but almost always including nasal (hoarse) notes
Note the following features :
- Typically , includes nasal notes (with several visible harmonics) “kiêêê”, more similar to a Blackbird (Turdus merula) than to a Robin (Erithacus rubecula). Those notes sound buzzy in comparison to the pure notes of Blackcap
- Many notes often sound like trills or buzzing notes (very fast modulations, see at 1.6 and 2.1 sec on the spectrogram above) , which almost never happens in Blackcap, once again contrasting with the “pure” Blackcap notes
- The phrases are often shorter than Blackcap, and separated by shorter breaks, so that Garden warbler sounds more in a hurry than Blackcap.
- The structure is the same throughout all the song (no visible evolution)
- Wider frequency range than Blackcap : 1-7kHz