By Mark Constantine and The Sound Approach

If there is a personal hell waiting for me it will be an ever-repeating day where I misidentify a Eurasian Blackcap Sylvia atricapilla song over and over and over again while repeatedly saying quietly and under my breath, “f*ck, f*ck fuckity f*ck”.

Eurasian Blackcap Sylvia atricapilla Texel, Noord-Holland, Netherlands, 28 October 2013 (René Pop)

When we published The Sound Approach to birding (Constantine & The Sound Approach 2006) I had got to grips with part of the problem (caused by the similar-sounding song of Garden Warbler S borin) when I explained how as Blackcaps move through Europe to their breeding grounds we experience their subsongs, plastic songs and crystallised songs. Here are the examples we gave.

  • 00:00

  • 00:00

  • 00:00

1 Eurasian Blackcap Sylvia atricapilla Ijmuiden, Noord-Holland, Netherlands, 5 September 2004 (Magnus Robb). Subsong of a first winter during autumn migration. Background: Common Chiffchaff Phylloscopus collybita and Western Jackdaw Corvus monedula. 04.040.MR.13840.11

2 Eurasian Blackcap Sylvia atricapilla Monte Gordo, São Nicolau, Cape Verde Islands, 16 February 2004 (Magnus Robb). Near-continuous plastic song. Background: distant village sounds. 04.004.MR.04138.11

3 Eurasian Blackcap Sylvia atricapilla Longbredy, Dorset, England, 3 June 2001 (Mark Constantine). Crystallised song of an adult male in June. Background: Common Wood Pigeon Columba palumbus, Eurasian Wren Nannus troglodytes, Dunnock Prunella modularis, Western Jackdaw Corvus monedula, Rook C frugilegus and Common Chaffinch Fringilla coelebs. 01.011.MC.00700.10

That was back in 2006 when the big news was the increasing number of Blackcaps overwintering in Britain. Ringing records had shown that two groups of birds that both bred in central Europe were wintering separately in Spain and Britain. There was even a suggestion that the two populations were on diverging paths and that if this continued they could be starting to separate as species. Blackcaps were hanging around our gardens, and on sunny winter days they were singing long, warbling subsongs somewhere intermediate between examples 1 and 2 above.

Now breeding Blackcaps are grabbing the headlines simply by being everywhere all of the time, as the explosion of breeding Blackcaps throughout southern Britain continuous apace. With many British breeding birds in decline, the Blackcap is making hay while its competitors for food and space struggle. Making a mockery of a series of papers showing how deer grazing has reduced warbler habitat, homesteading Blackcaps don’t care.

There has been a 120% increase in breeding pairs in SW England over the last 20 or so years, and they are still expanding at the same 5% a year… 44 years ago the BTO atlas (Sharrock 1976) estimated 200,000 pairs in Britain; by 2016 up to 1,7 million pairs (BTO BirdFacts), which presumably puts us around two million pairs today. A similar thing is happening in Holland where again Blackcap pairs are increasing by 5% every year, to the point that they now have half a million pairs.

Eurasian BlackcapSylvia atricapilla Texel, Noord-Holland, Netherlands, 3 April 2006 (René Pop)

This is a big deal for those of us birding by ear. Blackcaps sing rich, far-carrying and varied songs from at least January to August and seemingly for most of the day. Long warbling sub-songs in March (first recorded by Ludwig Koch), song battles throughout the spring and short punchy songs in July. That’s millions of extra Blackcap songs in Britain any minute of the day for at least half the year.

Professor Hartshorne in his book Born to Sing (1973) had a go at surveying all the birds of the world’s songs and came up with a list of the finest 200. There in among Common Nightingale Luscinia megarhynchos and Song Thrush Turdus philomelos is the Blackcap.

Adult Blackcaps have two main singing styles, which they often sing one after the other without a break, always in the same order. The first part and the bit that always catches me out is warbled and rambling, often full of mimicry of other birds, including scratchy sounds that can sound like an unknown finch or some other Sylvia warbler. The second, very familiar style is whistled and concise, usually lasting under 2 seconds; it is also the louder of the two. A classic Blackcap song can consist of several seconds of quiet warbling followed by less than two seconds of loud whistling. Magnus suggests that it’s as if the Blackcap first shares its thoughts in a rambling way and then, having reached a conclusion, ends with a concise, definitive statement.

  • 00:00

4 Eurasian Blackcap Sylvia atricapilla Pollença, Mallorca, Spain, 12:26, 8 May 2016 (Magnus Robb). Classic two-part song with a longish section of warble followed by a short whistle in each strophe. Background: Common Nightingale Luscinia megarhynchos and Common Chaffinch Fringilla coelebs. 160508.MR.122602.00

You might wonder if the first part is to attract a mate and the other to defend a territory. Researchers agree that warble and whistle are likely to be for different audiences, though they do not agree about who those are. One group of researchers (Leedale et al 2015) found that males increased the length of the whistle but not the warble after playback of other males’ songs, suggesting that whistling is primarily for a male audience. Meanwhile, Linossier et al (2015) tried playback of warble and whistle separately, and noted that males responded to both, using both parts in response, implying that each had a role in male-male communication. They suggested that the segregation of the two styles could be related to public (longer-range) versus private (shorter-range) communication, with both parts having something to say to both sexes.

Thinking about it, once the winter subsong period is over I really like to identify my Blackcaps by listening out for the whistled bit… It’s pretty straightforward and relatively unmistakable and I'm sure many of us do it by listening out for the combo: warbling and whistling.

Perhaps this is where the misery comes in because there are two ways that Blackcaps diverge from the classic, balanced, two-part pattern, each of which emphasises one of the two singing styles at the expense of the other. In the first of these, the song is almost all warble. When I depend on the whistled ending to identify the bird as a Blackcap, I can remain in limbo for a long time. The bird can warble happily away, imitating this and that for a half a minute or longer before doing a very brief whistle at the end, if at all. Since warbling is very similar to plastic song, it is not surprising that we hear more warble-heavy songs in the earlier part of the spring. However, if you were to follow the singing from a particular territory you might notice a return to lengthier warbles some way into the breeding season. We suspect that this signals the start of a second breeding attempt.

  • 00:00

5 Eurasian Blackcap Sylvia atricapilla Ooijpolder, Gelderland, Netherlands, 23 April 2003 (Magnus Robb). A song that is almost all warble with just the occasional bit of whistling (eg, at 0:17 and 0:52). Note the many imitations, eg,of Eurasian Skylark Alauda arvensis, Marsh Warbler Acrocephalus palustris, Eurasian Reed Warbler A scirpaceus and Common Nightingale Luscinia megarhynchos. Background: Greylag Goose Anser anser, Common Cuckoo Cuculus canorus and Eurasian Wren Nannus troglodytes. 03.011.MR.05253.11

Then by contrast there are songs that consist almost entirely of whistling, with little or no warbling preceding it. We hear these most often in the later stages of the breeding cycle. In July or early August for example, these tend to be the only kind of Blackcap songs that we hear. Later in the breeding cycle, territorial defence is going to be far more important than mate-attraction, so if whistling is all that’s left this does suggest that Leedale et al (2015) were right, and whistling is primarily about male-to-male communication. Neighbouring males often match syllables of whistled songs, whereas warbling seems to be more versatile. As a result, whistles can sound rather similar at a given site, but quite different from one location to another. Now, while I don’t want to confuse you, all this does explain my “F*ck, fu*ck, fuckity f*ck”.

  • 00:00

6 Eurasian Blackcap Sylvia atricapilla Pollença, Mallorca, Spain, 08:40, 18 May 2017 (Magnus Robb). Songs that consist almost entirely of whistling, with the only ‘warble’ sometimes preceding this (actually just in the last three songs) being a brief imitation of a Common Blackbird Turdus merula. Background: Mallard Anas platyrhynchos, Cetti’s Warbler Cettia cetti, European Goldfinch Carduelis carduelis and European Serin Serinus serinus. 170518.MR.084006.00



Over the past 20 years, The Sound Approach has specialised in bird sounds of the Western Palearctic, collecting over 71,500 recordings. That makes ours the fourth largest collection of wild bird recordings in the world, and one of the only ones where every recording is digital, stereo, fully documented and often sexed, aged and photographed. We sincerely hope that virtually all are correctly identified too. We have recorded 95% of the species in the Collins bird guide to Britain and Europe and are working hard on the other 5%.

One of the things we do with this collection is to search for ‘SHIPS’ (Species Hiding In Plain Sight), and Blackcap popped up on our radar because some Blackcaps sing a very different song from the others.

Eurasian BlackcapSylvia atricapilla Texel, Noord-Holland, Netherlands, 15 October 2013 (René Pop)

I hadn’t realised before I started this series of articles how much of my life I have spent taking holidays in Pollença, Mallorca. There on my 51st birthday (2004), I remember I was not having a particularly good day. My three teenage kids were on my case for some reason - I think the villa we were renting wasn’t any good - and I distinctly remember escaping into the garden with my recording gear. There I recorded Blackcap’s leiern song, described by Shirihai et al in Sylvia warblers (2001) as “a regional dialect from parts of western Europe”. According to C F Mason’s monograph The blackcap (1995), it was first described from the Alps. I wanted in later years to go back to this villa, but I could never find it or the group of Blackcaps that had sung this unusual song.

  • 00:00

7 Eurasian Blackcap Sylvia atricapilla Pollença, Mallorca, Spain, 06:00, 21 July 2004 (Mark Constantine). Whistledsong of a male, with leiern motif starting after 14 seconds and closely resembling song of Great Tit Parus major. Other Blackcaps reply with leiern motif at a distance. Background: Common Wood Pigeon Columba palumbus, fledgling Common Blackbird Turdus merula, Sardinian Warbler S melanocephalus and House Sparrow Passer domesticus. 04.017.MC.01230.11

Suddenly in the midst of a typical Blackcap phrase appears a motif that could be described as a fast tea-cher, tea-cher, tea-cher. This particular kind of whistle-song sounds like an amalgamation of Great Tit Parus major and Blackcap songs. Occasionally the leiern motif appears on its own for a song or two, before more typical Blackcap whistles resume. This could certainly involve mimicry but sounds far too distinctive to be a regional dialect. I may have mentioned before how much I hate it when something is dismissed as a dialect. I really think there is no aspect of biology that lacks a purpose, and I can really find no purpose to a regional dialect. Anyway, fast forward to July 2015 and I am again in Mallorca, this time staying at Llenaire, a boutique hotel set in acres of organic farmland with 200 pure bred Mallorcan sheep, sizeable vegetable gardens and countless almond, fig, lemon, olive and orange trees. And there in the olive trees are several Blackcaps singing the leiern song.

  • 00:00

8 Eurasian Blackcap Sylvia atricapilla Pollença, Mallorca, Spain, 07:58, 15 June 2017 (Magnus Robb). Whistled song without warbling preamble, with leiern motifs at 0:02, 0:10, 0:26, 0:34 and 1:01. Background: Cetti’s Warbler Cettia cetti, Sardinian Warbler S melanocephala and Common Nightingale Luscinia megarhynchos. 170615.MR.075838.01

I phoned Magnus… let's sort this out! Magnus booked into the hotel a couple of weeks later and chatted to the owners, and we got permission to start a study.

In Mallorca in spring, Blackcaps that have wintered in Africa pass through on migration. Blackcaps that have wintered in the Balearics sing before leaving, and then there are the Blackcaps that are resident on the island. The local ringers often catch these birds and had noticed that they have shorter wings than migrant and wintering Blackcaps. Aha… what if they also sing a different song! Magnus contacted Mallorca-based ringer Steve Nicoll, who recruited a team of local ringers. We got permission to put colour rings on the birds at Llenaire that sang leiern songs, and take a DNA sample. We recorded the songs of these colour-ringed birds and sent the samples to Aberdeen University for genetic analysis.

Magnus hears things differently from you and I. He told me that his local Blackcaps in Portugal are keen leiern-singers, though with each two-note repetition rising, not falling. Hmmm, really … now there are none so deaf as those that won’t hear… “It doesn’t sound like it to me” I said. Magnus became quite sceptical that there would be any genetic difference between birds from Mallorca and elsewhere. However, looking at cytochrome b, a region of mitochondrial DNA, Thom Shannon and Martin Collinson in Aberdeen did find a small but consistent difference. All the leiern-singing Mallorca birds are very slightly but consistently genetically distinct from Blackcaps from anywhere else. It’s only by 2-4 base pairs (0.3%, compared to a difference of around 5% between Spotted Flycatcher Muscicapa striata and Mediterranean Flycatcher M tyrrhenica), so not expected to be species-level divergence, at present (Thom Shannon PhD thesis in prep).

By now Magnus and Arnoud keep on playing me examples of leiern song from all over the place. Magnus believes that leiern song is a throwback to a Sylvia ancestor, and that several other Sylvia warblers such as Lesser Whitethroat S curruca have faster versions of the same thing in their songs.

  • 00:00

9 Eurasian Blackcap Sylvia atricapilla Castricum, Noord-Holland, Netherlands, 12:15, 23 May 2019 (Arnoud B van den Berg). A male singing leiern-song in birder Gerald Oreel’s garden. 190523.AB.121500.22

I remain sceptical, preferring to believe this is a Balearic phenomenon, until one day when I am recording a stunning set of Blackcap songs in Dorset, literally in my own back yard, and yes there, quite clearly, over and over again, is the leiern song. Later we listened together and laughed at my stubbornness. My dreams of having a new species of Blackcap - “Constantine’s Warbler” - lay in tatters, and at my own hand. Well for the moment at least. After all we haven’t really answered which came first, the song of the Balearic Blackcap, or the songs of the Blackcaps in the rest of the world.

  • 00:00

10 Eurasian BlackcapSylvia atricapilla Wareham, Dorset, England, 05:30, 12 May 2019 (Mark Constantine). Song including three different kinds of leiern-motifs, recorded by the author on his own land. Background: Common Wood Pigeon Columba palumbus, Eurasian Blue Tit Cyanistes caeruleus, Common Blackbird Turdus merula, European Goldfinch Carduelis carduelis and Common Reed Bunting Emberiza schoeniclus. 190512.MC.053000.22

Film and Literature:

High Fidelity (2000) opening line: “Which came first, the music or the misery?”

Two weddings and a funeral (1994) opening line: “Fuck fuck fuckity fuck.”

Constantine, M & The Sound Approach 2006. The Sound Approach to birding. Poole.

Hartshorne, C 1973. Born to sing: an interpretation and world survey of bird song. Bloomington.

Leedale, A E, Collins, S A & de Kort, S R 2015. Blackcaps (Sylvia atricapilla) increase the whistle part of their song in response to simulated territorial intrusion. Ethology 121: 403-409.

Linossier, J, Courvoisier, H & Aubin, T 2015. The two parts of the blackcap song: Acoustic analysis and male responses to playbacks. Behavioural Processes 121: 87-92.

Mason, C F 1995.The blackcap. London.

Sharrock, J T R 1976.The atlas of breeding birds in Britain and Ireland. London.

Shirihai, H, Gargallo, G, Helbig, A J, Svensson, L & Harris, A 2001. Sylvia warblers: identification, taxonomy and phylogeny of the genus Sylvia. London.