I’ve only heard the song of a nightingale once in real life, last spring near a beach in Mallorca, so I am convinced that the blackcap’s song can be described as Ireland’s nightingale. I’ve now heard it everywhere over the past six weeks. Perhaps its song has simply lodged in my mind since I first noticed it, persistent, echoing endlessly, but I can’t help but feel that the blackcap is more common this year.
A few weeks ago, during a walk down Glencree Valley towards the river below, the melodic and distinctive warble of a blackcap poured out of a nearby hedge. With precision and pace, each note unfurled with crystalline clarity, the sound resonating so loudly it felt like the bird was standing just a metre away from me. Yet, despite remaining still and scanning every corner of the thicket and the trees beyond, I failed to spot it. All I heard was the song; it was as if someone had pressed play on a set of next-generation cutting-edge speakers crafted for perfect, flawless sound.
Weighing no more than a chocolate bar, the blackcap is an astonishingly small creature, considering the sonorous beauty it creates. Its back, wings and rounded body are covered in olive-grey plumage, contrasting with a sleek, dark cap on its head – brownish for females, a deep black for males.
At home they’ve made a small corner of the nearby public field their own, in an area left to trees, brambles and ivy. In spring and summer, they vanish into these pockets of dense woodland undergrowth to build their nests and search for caterpillars, spiders and beetles. By late summer, they’ll also take elderberries, hawthorn berries and blackberries.
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Until relatively recently, blackcaps were only ever summer migrants to Ireland, arriving from their wintering grounds in the Mediterranean and sub-Saharan Africa to breed. However, something has changed over the past five decades: an increasing number are spending their winters in Ireland and Britain. Between 1981 and 2011, their winter range has expanded by 77 per cent. Since 1980, the blackcap population across Europe has surged by 155 per cent, transforming what was once a rare winter visitor into a now-established presence.
We think of evolution as a slow process unfolding over thousands of years, but the blackcap is a striking example of how, in just a short time, it has rapidly evolved to thrive in a human-dominated world. Two key factors are at play: first, our rapidly warming climate, which is softening the severity of winter temperatures in northern Europe; and second, the blackcap’s skill at finding garden bird feeders during the colder months, which offers it something rarely if ever seen in nature: a reliable and plentiful supply of fat and protein-rich food over a period of months.
In the late 1970s, a small study reported increased blackcap numbers in Ireland during the winter. The researchers suggested that this was due to the birds’ adaptation to relying on food from garden bird tables. Over time, scientists have discovered that this might influence the course of evolution, leading to genetic differences between the birds that continue to migrate further south for the winter and those who spend the cold months in more northerly countries such as Ireland.
A 2021 study by researchers at Cornell University’s renowned Lab of Ornithology in Ithaca, New York, surveyed 59 gardens and local park sites across Ireland and Britain for blackcaps. These birds were ringed between November and April, and volunteers helped by recording sightings of the ringed birds at feeders. Over four winters, nearly 10,000 records were collected, tracking the movements of 600 birds.
The blackcaps were altering their migration patterns, embarking on an unusual northward journey in search of bird feeders stocked with high-energy foods such as suet balls. During the winter, blackcaps who come to Ireland and Britain have discovered the key to a comfortable life: a constant food supply. This shift may also be influencing their physical traits, as blackcaps relying on feeders have been found to have more rounded wingtips and longer bills, possibly linked to a more generalist diet – an example of a species thriving in a world changing at an unprecedented pace (although tragically, far outnumbered by the number of species who are disappearing for the same reason).
In the oak wood of Glencree, the blackcap’s song unfolds in two distinct parts. The first section is a meandering, somewhat hesitant melody, like someone quietly murmuring to themselves, before the main song kicks in, when the bird belts out its powerful tune into the morning air, proving itself to be one of our finest songsters.
For those of you without these virtuoso singers nearby, search for their songs on xeno-canto.org, the citizen science repository of bird calls, where there are magical recordings of the blackcap to enjoy.
