Birds
Blackcap
Sylvia atricapilla · also called Eurasian blackcap
A blackcap is a plain, skulking little warbler with a song good enough to earn it the nickname the northern nightingale. It is also one of the clearest examples anywhere of evolution happening in real time: within the space of a few decades, a growing share of the population has switched which direction it migrates, and the two groups are already becoming genetically distinct.
Overview
The blackcap, Sylvia atricapilla, is a small warbler of woodland, scrub, and overgrown gardens across Europe, western Asia, and North Africa. The male has a solid black cap, the female a chestnut one — the simplest way to sex the bird. It eats insects in summer and switches to berries, and now increasingly garden feeders, in the colder months.
A migration route splitting in two
Traditionally, northern blackcaps flew south-west to winter around the Mediterranean. Since the mid-20th century, a growing number instead fly north-west to Britain and Ireland, and studies of ringed birds show this is a genuine, inherited difference, not just a behaviour change. Because the two groups return to breed at different times, they increasingly pair within their own route, and the wintering populations are becoming genetically distinct — a rare, directly observed case of a new migratory divide forming within living memory.
Status
Least Concern and increasing — one of the clearer songbird success stories in Europe, aided in part by the newly evolved population wintering in milder, feeder-supplied British gardens rather than making the longer journey south.
Blackcap: common questions
How do you tell a male and female blackcap apart?
By the colour of the cap. A male blackcap has a solid, glossy black cap running from the base of the bill back over the crown to just above the eye, standing out clearly against otherwise plain grey-brown plumage. A female, and young birds of both sexes before their first proper moult, have a warm reddish-brown or chestnut cap in the same position instead of black. This is one of the more straightforward and reliable ways to sex a small warbler at a glance, since the rest of the plumage in males and females is broadly similar.
Why are some blackcaps now spending winter in Britain instead of migrating to Africa?
Studies tracking ringed birds and analysing their genetics have found that this is a real, evolving split in migratory behaviour rather than simply older or different individuals changing their minds. A growing subset of blackcaps that breed in central Europe now fly north-west to winter in Britain and Ireland instead of the ancestral route south-west to the Mediterranean and North Africa, and because these birds return to the breeding grounds earlier in spring, they tend to pair up with other birds that took the same new route, gradually making the two wintering populations more genetically distinct from one another over time.
Why is the blackcap sometimes called the northern nightingale?
The nickname reflects the very high regard in which birdwatchers and naturalists hold the blackcap's song, which is rich, varied, and fluting, delivered in a way that some listeners find comparable in quality to the celebrated song of the true nightingale, a different and more southerly distributed species. Because the blackcap breeds much further north and is far more widespread across Britain and northern Europe than the nightingale, for many people it serves as the best, most accessible equivalent of a truly outstanding songbird performance, hence the affectionate comparison.
Do blackcaps come to garden bird feeders?
Increasingly, yes, especially the birds that now spend the winter in Britain and other parts of north-western Europe rather than migrating to the Mediterranean. These wintering blackcaps have been recorded taking fat balls, suet, sunflower hearts, and other typical garden bird-table food, a relatively recent and still-growing behaviour that appears to be helping this particular population survive the winter and may be part of what is reinforcing their preference for the shorter, milder migration route in the first place.