A strong pair of lungs are needed for the powerful song this species uses to fend off rivals and also attract female partners
Its powerful song belies its small appearance, and this is one bird that’s on the rise
IALWAYS KNEW THAT Cetti’s Warblers had loud songs, but genuinely didn’t realise quite how loud until May this year. I was at Cetti Central, also known as Radipole Lake, in Dorset, and was innocently walking down one of the paths enclosed on either side by scrub-fringed reedbeds, trying to listen for Bearded Tits. It was here that I was subjected to a verbal assault. Unknowingly, I had stumbled close to a singing post of a Cetti’s Warbler that was right next to the path, so, when it sang, it was no more than a metre away.
Honestly, that first note made me recoil. It was like a fire alarm going off. The vehemence of the explosion of song almost swept me off my feet. This piece of reed rage was extraordinary. Ironically, I had just been involved in a delightfully intellectual conversation about what piece of music resembles the Cetti’s Warbler’s brief, distinctive outburst. The rhythm of some singers is quite similar to the famous opening gambit of the first movement of Mozart’s Eine Kleine Nachtmusik, although the bird is much more forceful than the elegant piece. Alternatively, the fantastic flourish that opens Grieg’s piano concerto at least recalls the unexpected power of the bird’s phrase. The Cetti’s Warbler’s intervention felt like a jolt of heavy metal to explode the cultural hot air. That’s one thing we all know about Cetti’s Warblers; they have loud songs, with a particularly strong opening and then a few notes followed by quite a dramatic fade – a vocal short-lived firework. These songs, moreover, are given lustily all year round apart from a break in the summer. Another thing we learn very quickly is that, despite their vocal presence, these birds are incredibly skulking. They spend most of their time out of sight, and can be extremely difficult to see. This is at odds to their dominance of the airwaves, in a similar vein to the Nightingale. Not many human loudmouths remain in the shadows, skulking, so it seems counterintuitive to us that such an obvious presence should remain out of sight. As it happens, Cetti’s Warblers are retiring, but they aren’t shy. Their tendency to remain in cover has little to do with a need to be hidden, but is instead an ecological imperative. People often
comment, when they do finally set eyes on one, that Cetti’s Warbler resemble Wrens, with their cocked up tails; and there are marked similarities between the two unrelated species. It is even possible that they might at times exclude each other from feeding sites. The Cetti’s Warbler obtains most of its food by hopping on the ground deep within the vegetation, or by clinging to stems just above the water surface. Its true habitat lies at the base of thickets which are close to water. One of the best ways to see one, especially in the winter, is to keep a close eye on vegetation right at the edge of water, either a lake or a slow flowing river. Wrens feed here, too. The Cetti’s Warbler feeds entirely on invertebrates throughout the year, and is apparently noted for the wide variety it takes, in shape and size. It has a predilection for damselflies in the summer, but will also take minute food items, including aphids. It will take some aquatic larvae, suggesting that at times it is perfectly happy to get its large, strong feet wet.
Once you realise the true habitat of the Cetti’s Warbler, the loudness of its song begins to make sense. Birds which skulk often have powerful voices, because they need to get their signals heard even from deep within low vegetation – this is obviously the case in Wrens, which are so famous for their outbursts. Although such birds must sometimes come across each other in the labyrinth, most communication to rivals or mates is vocal. There is another potential reason for the loud song, and it is an intriguing one. It seems that, on the whole, Cetti’s Warblers hold relatively large territories throughout the year – evidently a single territory can extend in linear fashion for several hundred metres, and it is routine for a bird to cover 100 metres on its own. It is hard not to conclude that having a good pair of lungs is necessary for a bird with a big territory to keep rivals off its patch. There is an interesting case recorded from the continent of two Cetti’s Warblers involved in a day-long song duel. In contrast to the intense, close-up song duels we might witness among Robins, these birds remained 300 metres apart and just shouted at each other! The singing method of Cetti’s Warblers is very unusual, as anybody who has encountered them will know. They are completely different from most birds, which sing continuously and often conspicuously from a high perch. Cetti’s, on the other hand, sing one or perhaps two song phrases, well within cover, and then tend to fall silent for quite some time. After a minute or two (up to 14 minutes has been recorded) it will then sing again, just as loudly and abruptly, but from a completely different place. A Cetti’s Warbler will have a
number of favoured song posts in its territory, of which about 10 are favourites, and they are often 100 metres or more apart. The bird plies the beat of its territory, singing intermittently, and sparingly, as it goes. Presumably this is the way a male can cover its area. But why would a bird like a Cetti’s Warbler need a large territory? Well, it could be simply to satisfy its feeding requirements, particularly during the winter, when invertebrates are literally thin on the ground. In the breeding season, however, there is another possible reason. Cetti’s Warblers are highly prone to polygamy. And if you want to attract plenty of talent to your territory, presumably it pays to point out metaphorically to the land that you own. A large territory could be a male’s selling point. And, at the same time, who’s to say that a large territory doesn’t help to keep the women apart and conflicts at a minimum? Research into Radipole Lake Cetti’s Warblers found that most males are polygamous. Of 125 territorial males counted there, 70 were paired to more than one mate, usually just to two, but occasionally up to four. These females would all be nesting at approximately the same time, and the territories of each male were exclusive. It is thought that at the beginning of the breeding season there are more females in the population than males, allowing the possibility of polygamy. Bizarrely, the males are all much heavier than the females, by a factor of a quarter. Is this a further attractant? Nobody knows. What we do know, though, is that every male Cetti’s Warbler is predisposed to attracting more than one female to its territory. And intriguingly, the birds seem to do this mainly at night. During the day, the song is generally directed towards the rival males, to keep them in check. But in the hours of darkness, the song is directed towards attracting unpaired females. That, therefore, might solve our classical music puzzle. What is better for beguiling a listener than a Little Night Music?
A Cetti’s Warbler will have a number of favoured song posts in its territory, of which about 10 are favourites, and they are often 100 metres or more apart
BIGMOUTH The Cetti’s Warbler is the classic small bird with a big voice
Radpole Lake, Dorset
YOU’D BE LUCKY! Cetti’s Warblers rarely show themselves this well in ‘real life’ When seen well, the Cetti’s Warbler is a handsome, though simply patterned bird SUBTLE BEAUTY
The obvious pale supercilium and cocked tail give Cetti’s Warblers a certain Wren-like look