Eurasian Blackcap

Identification

The blackcap is a mainly grey warbler with distinct male and female plumages. The nominate subspecies is about 13 cm (5.1 in) long with a 7–8 cm (2.8–3.1 in) wing length. The weight is typically 16–25 g (0.56–0.88 oz), but can be up to 31 g (1.1 oz) for birds preparing to migrate. The adult male has olive-grey upperparts, other than a paler grey nape and a neat black cap on the head. The underparts are light grey, becoming silvery white on the chin, throat and upper breast. The tail is dark grey, with an olive tint to the outer edge of each feather. The bill and long legs are grey, and the iris is reddish brown. The female resembles the male, but has a reddish-brown cap and a slightly browner tone to the grey of the upperparts. Juveniles are similar to the female, but their upperparts have a slight rufous tinge, and the breast and flanks have a more olive tone; young males have a darker brown cap than their female counterparts. This species is unmistakable; other dark-headed Sylvia species, such Sardinian and Orphean warblers have extensive black on the head instead of a small cap. They are also larger and have white edges on the tail.<p>Blackcaps have a complete moult in their breeding areas in August and September prior to migration. Some birds, typically those migrating the greatest distances, have a further partial moult between December and March. Juveniles replace their loosely structured body feathers with adult plumage, starting earlier, but taking longer to complete, than the adults. Blackcaps breeding in the north of the range have an earlier and shorter post-juvenile moult than those further south, and cross-breeding of captive birds shows that the timing is genetically controlled.<p>The male's song is a rich musical warbling, often ending in a loud high-pitched crescendo, which is given in bursts of up to 30 seconds. The song is repeated for about two-and-a-half minutes, with a short pause before each repetition. In some geographically isolated areas, such as islands, peninsulas and valleys in the Alps, a simplified fluting song occurs, named the Leiern (drawling) song by the German ornithologists who first described it. The song's introduction is like that of other blackcaps, but the final warbling part is a simple alternation between two notes, as in a great tit's call but more fluting. The main song is confusable with that of the garden warbler, but it is slightly higher pitched than in that species, more broken into discrete song segments, and less mellow. Both species have a quiet subsong, a muted version of the full song, which is even harder to separate. The blackcap occasionally mimics the song of other birds, the most frequently copied including the garden warbler and the common nightingale. The main call is a hard tac-tac, like stones knocking together, and other vocalisations include a squeaking sweet alarm, and a low-pitched trill similar to that of a garden warbler.<p>Male blackcaps will sometimes sing even when incubating, especially with the second brood. This appears to be intended to maintain the bond with the female. Wintering birds in Africa are quiet initially, but start singing in January or February prior to their return north.

Taxonomy

The genus Sylvia, the typical warblers, forms part of a large family of Old World warblers, the Sylviidae. The blackcap and its nearest relative, the garden warbler, are an ancient species pair which diverged very early from the rest of the genus at between 12 and 16 million years ago. In the course of time, these two species have become sufficiently distinctive that they have been placed in separate subgenera, with the blackcap in subgenus Sylvia and the garden warbler in Epilais. These sister species have a breeding range which extends farther northeast than all other Sylvia species except the lesser whitethroat and common whitethroat. The nearest relatives of the garden warbler outside the sister group are believed to be the African hill babbler and Dohrn's thrush-babbler, both of which should probably be placed in Sylvia rather than their current genera, Pseudoalcippe and Horizorhinus respectively.<p>The blackcap was one of the many bird species originally described by Carl Linnaeus in his landmark 1758 10th edition of Systema Naturae, as Motacilla atricapilla. The current genus name is from Modern Latin silvia, a woodland sprite, related to silva, a wood. The species name, like the English name, refers to the male's black cap. Atricapilla is from the Latin ater, "black", and capillus, "hair (of the head)".<p>Fossils and subfossils of the blackcap have been found in a number of European countries; the oldest, dated to 1.2–1.0 million years ago, are from the Early Pleistocene of Bulgaria. Fossils from France show that the genus Sylvia dates back at least 20 million years.<p>The differences between subspecies are small, making subspecific boundaries hard to define, and the exact distribution of S. a. heineken is unclear, since birds from northwest Africa may be of this form. About 2% of male blackcaps on Madeira and the Azores are melanistic, with black plumage on the whole head and upper breast. Melanistic females are rarer, and are characterised by grey-brown underparts. This dark morph has also been recorded from the Canary Islands, but not from Cape Verde. The melanistic birds were formerly sometimes considered to be a distinct subspecies, S. a. obscura.

Scientific name

Sylvia atricapilla

Authority

(Linnaeus, 1758)

Order

Passeriformes

Family

Sylviidae

Genus

Sylvia

Range and habitat

The continental breeding range of the blackcap lies between the 14–30° July isotherms, and is occupied by the nominate subspecies, the other forms being restricted to islands or fringe areas in the Caucasus and eastern Iberia. Birds on the Mediterranean and Atlantic islands and in the milder west and south of the main Eurasian distribution often winter within the nesting range, but populations elsewhere are migratory. The blackcap is a leap-frog migrant; birds from the north of the breeding range travel furthest south, whereas Mediterranean breeders move much shorter distances. The wintering areas overlap with the breeding range, but also include extensive areas in West Africa, East Africa south to Lake Malawi, and further north in Ethiopia, South Sudan and Eritrea. The large majority of birds wintering in eastern Africa are of the southwest Asian race, S. a. dammholzi.<p>There is a migratory divide in Europe at longitude 10–11°E. Birds to the west of this line head southwest towards Iberia or West Africa, whereas populations to the east migrate to the eastern Mediterranean and on to East Africa. Cross-breeding in captivity of birds from the resident population on the Canary Islands with migratory blackcaps from Germany showed the urge to migrate is genetically controlled, the offspring showing intermediate behaviour in terms of restlessness at migration time. Similar experiments using birds from southern Germany and eastern Austria, on opposite sides of the migratory divide, demonstrated that the direction of migration is also genetically determined. Climate change appears to be affecting the migration pattern of the garden warbler and blackcap. Both are arriving in Europe earlier than previously, and blackcaps and juvenile (but not adult) garden warblers are departing nearly two weeks later than in the 1980s. Birds of both species are longer-winged and lighter than in the past, suggesting a longer migration as the breeding range expands northwards.<p>In recent decades, substantial numbers of continental European birds have taken to wintering in gardens in Great Britain, and, to a lesser extent, Ireland, where the blackcap was formerly just a summer visitor. Although the British climate is sub-optimal, compensatory factors include the ready availability of food, (particularly from bird tables), a shorter migration distance, and the avoidance of the Alps and the Sahara Desert.<p>It was originally thought that most of these wintering birds come from Germany, and isotope analysis (which enables the wintering location to be determined) showed that the continental birds wintering in Britain tend to mate only among themselves, and do not usually interbreed with those wintering in the Mediterranean or western Africa. This is because the British migrants arrive back on the breeding grounds earlier than blackcaps wintering around the Mediterranean, and form pairs before the southern birds arrive. Mixed pairings are also selected against because the hybrid young would migrate in an intermediate direction, which would take them into the Bay of Biscay.<p>It now appears that the wintering birds in the UK come from a much wider area than previously thought. The majority come from France, and some individuals come from as far away as Spain and Poland. The steady supply of winter food in gardens gives even Spanish-breeding birds an opportunity to put on weight quicker than in their home range.<p>A 2021 paper showed that blackcaps, particularly adults, wintering in Britain and Ireland showed high site fidelity and low movement between wintering sites, in contrast to blackcaps wintering in their traditional winter ranges. Adults that frequented gardens had better body condition, smaller fat stores, longer bills, and rounder wing tips. The bill and wing tip shapes reflected a more generalist diet than that of birds in traditional winter sites.<p>Blackcaps did not exclusively feed in gardens; visits were linked to harsher weather. Individuals generally stayed at garden sites until immediately before spring departure, and supplemental feeding may have benefits for winter survival, When preparing for migration, abundant supplemental food may allow blackcaps to attain better body condition and may facilitate earlier and more successful breeding attempts.<p>In the Iberian Peninsula, migratory blackcaps (and European robins) track similar climatic conditions over the season, which sedentary individuals must cope with great variation in climate over the year. This suggests a trade-off between the cost of travelling long distances of migrants, and the flexibility required by sedentary individuals to tolerate a wide variety of environmental conditions.<p>The blackcap's main breeding habitat is mature deciduous woodland, with good scrub cover below the trees. Other habitats, such as parks, large gardens and overgrown hedges, are used as long as they meet the essential requirements of tall trees for songposts and an established understory. Where other Sylvia warblers also breed, blackcaps tend to use taller trees than their relatives, preferably those with a good canopy, such as pedunculate oak. In prime habitat, breeding densities reach 100–200 pairs per square kilometre (250–500 pairs per square mile) in northern Europe, and 500–900 pairs per square kilometre (1,250–2,250 pairs per square mile) in Italy. Densities are much lower in poorer habitats such as conifer forests. Breeding occurs in Europe at altitudes up to 2,200 m (7,200 ft).<p>The preferred winter habitat around the Mediterranean is scrub and olive orchards, where densities approach the levels found in the best breeding areas. The British wintering population is atypical, with 95% found in gardens, mostly in towns at altitudes below 100 m (330 ft). In Africa, habitats include cultivated land, acacia scrub, mangroves and forest, and these warblers are found at altitudes up to 3,600 m (11,800 ft) in the east of the continent. Wintering birds wander in search of good fruit supplies, but often stay in good feeding areas, and return in subsequent winters. Migrants may occur in a wide variety of habitats, such as reed bed and fen, but show a preference for shrubland.

Breeding range

PAL : c, w, sw

Non-breeding range

n, e, w AF

Migration

Complete migrants

Behavior

Migration pattern: Complete migrants.

Conservation

Population trend: rising.

Population trend

rising