Blackcap: bird song and calls

By James Duncan

Communities and Wildlife Officer

Blackcap (Sylvia atricapilla)

The Blackcap, a distinctive member of the 'Old World' warbler family Sylviidae. Members of the genus Sylvia are generally referred to as 'typical' warblers, five of which breed in Britain. The Blackcap is one of a good number of bird species named after a distinctive and defining visual characteristic, its black cap. Ironically it isn't the only British bird to display this trait, which could very well be labelled at either Marsh or Willow Tit to name a couple of examples. The black cap is also entirely restricted to the adult male, for the female displays a russet-brown cap - even the juveniles resemble a female, prior to the gradual appearance of black feathers when moulting. The Blackcap is an adaptable species found occupying a range of habitats, with a preference for mixed deciduous woodland with understory, though essentially anywhere with a mix of trees and bushes. Amongst our thirteen regular breeding warblers, their sheer adaptability sees them behind only Chiffchaff and (rapidly declining) Willow Warbler in total numbers, with approximately 1.6 million breeding territories in the UK. 

It's perhaps easy to think of the Blackcap as a typical summer migrant. Its arrival on our shores is certainly a wonderful harbinger of spring, but the simple fact is it's been undergoing a radical change in migratory habits. There's now a strong tendency for individuals to overwinter in Britain, and it's increasing likely you'll spot one in your garden at this time. Logic would dictate these birds are surely members of our breeding population choosing to stay. This is, however, not the case as the vast majority of British breeders head south for a warmer Mediterranean (or African) winter. The Blackcaps you see in winter are largely part of a central European (predominantly German) population, migrating specifically in autumn to gorge on garden handouts, fruit and berries, thriving in the warming conditions of our global climate amongst our temperate 'urban islands.' Once again the Blackcap's adaptability has assisted no end - it's far happier to diversify its diet away from the primarily insectivorous habits of its warbler relatives. Indeed it has a bolshie feeding reputation and may often be seen bullying other garden birds into submission, reluctant to give up a winter food source. The decision of these birds not to cross the Sahara has clear advantages for survival, but also enables a quicker return to breeding grounds. This undoubtedly helps males to obtain the very best breeding territories, heightening their breeding success and giving them a competitive edge over those which have returned from further afield.  

Truthfully, not all warblers warble. The Blackcap is certainly regarded as one of the finest songsters amongst its Sylvia relations, and is most definitely a warbling warbler. In fact its beautiful song, which so wonderfully typifies the arrival of spring, has over the ages been confused with that of the much rarer Nightingale. Indeed, alternative vernacular names have included 'mock', 'country' and 'northern' Nightingale, indicative of its fabulous abilities. A prime example can be seen by English poet John Clare, whose poem 'The March Nightingale' fails to distinguish the two species from one other. Ultimately, the Blackcap's cheery, 'fruity', liquid song is one of the most marvellous of the breeding season and its varying tempo is really distinctive once learnt. The Blackcap is a remarkably active, restless species and will usually sing from within cover, though often displays little hesitation to sing from an exposed perch. It's this habit that typically splits it from its shyer cousin, the unassuming Garden Warbler (Sylvia borin).

Listen to the song in this video below -

An important thing to realise is that Blackcap song generally comprises two distinct elements. The first section is a rambling, scratchy, subdued introduction to the main explosion of more rhythmic musicality. Owing to the quieter nature of this component, it may not be heard too distinctly if not in close proximity to the bird. It's usually quite typical for Sylvia warblers to have a 'scratchy' element to their song. This chatty preamble often resembles somebody talking incessantly to themselves at a rate of knots. Its only when this finishes that the Blackcap seemingly clears its throat and the true nature of the song is revealed, for its a pure melodic cascade of rich, warbling, flute-like notes. The pitch and tone display a strong resemblance to song produced by Blackbird, albeit one that's had its speed cranked right up. The richer notes certainly have a human quality and resemble somebody manically whistling whilst being jabbed in the back. The fluting segment tends to descend towards the finale and can be quite discordant, though if transliterated may read something like "fruity trooty rooty tooty too." Blackcap's are also adept mimics and other than producing Blackbird-esque vocals, will frequently imitate other warblers (particularly Garden, Reed and Whitethroat), Song Thrush and Nightingale (hence the confusion). As with other passerines, such as Chaffinch, regional dialects may be apparent within Blackcap song. Though not extensively studied, it's even possible that the scratchy intro may be used for mate attraction whereas the warbling section may be used territorially.

Listen to an extended version of the song below -

The subsong is a form often uttered by young birds and those outside of the breeding season. It may be given year-round and bears a distinct similarity to the preamble present in full breeding song, sounding low, chatty, fizzy and twittering, typically interspersed with yet more mimicry of other species. As a whole it's similar to that of its close relation, the Garden Warbler, though that'll be the subject of another blog. Newly arriving spring Blackcaps may also sometimes partake in a particularly rapid and extended subsong, though it's rare that they won't eventually intersperse some high-pitched whistling. 

Listen to an example of the subsong below -

The Blackcap may generate a perplexing variety of territorial calls, though the typical contact call is a hard, tongue-clicking "teck teck" which has a scolding quality to it. It's not dissimilar to the 'pebble-clacking' call of the Stonechat, though the stones sound as if they're being struck with greater ferocity. When excited or agitated this call gets repeated more rapidly and may well get louder too. 

Listen to this call below -

There may also be a number of diverse alarm calls delivered by a Blackcap, but by far the most frequently heard is that of the typical call (as above), delivered much more vigorously with an additional 'hoarse' and somewhat extended wheezy note. It may be transliterated to something like "teck-teck-teck-chreee." 

Listen to this call below -