This morning I heard my first Cetti’s Warbler of 2025, a welcome sign of the changing year. Cetti’s Warblers do sing during the winter, but only occasionally. As the days start to lengthen, so they start to sing more frequently, their explosive burst of song far-carrying and totally unmistakable. It was a welcome sound for other reasons, too. It was my 127th species of the year, while it was also confirmation that we still have these warblers in my local fen, as I only recorded the first one there in 2022.
Cetti’s warblers are relatively recent colonists of Britain, with the first recorded nest in Kent (the closest area of England to the continent) in 1973. This was at a reserve called Stodmarsh. I well remember my first encounters with the warblers in May that year. I was unaware of their presence, and also unfamiliar with the species, so I was puzzled at first as to their identity. My frustration was made worse by the fact that though there was a bird singing close by, and it was clearly moving around, I couldn’t get even a glimpse of it. At the time Cetti’s warblers were regarded as non-migratory birds that occurred no closer to Britain than central France, so their arrival wasn’t anticipated.
I can’t remember how long it took me and my companion to work out that the mystery singer was a Cetti’s warbler, but I believe that we did so quite quickly. After the initial breeding success, colonisation of suitable habitats in southern England was remarkably fast, though heavy snow in the late winter of 1987 virtually wiped out the Kentish breeding population. However, by then pairs had established themselves at numerous other sites in southern England, and many of these survived.
Today range expansion continues, and these warblers now breed widely in south-east and central England, along with southern Wales. The damp fen where I heard my singing bird this morning offers perfect habitat, and it’s something of a surprise that they took so long to establish themselves there.
Cetti’s (named after Fr Frances Cetti, 1726-1778, an Italian Jesuit priest and zoologist) are one of the most difficult birds to see, as they like to sing from deep, dense cover. If you do see one, then it’s usually just a glimpse of a small, reddish-brown bird, short-necked, broad-tailed and with short rounded wings. The shape and size of the wings indicate that this is a non-migratory species. I have found that these warblers usually sing from the same spot twice, then almost at once fly a short distance to another hidden perch. It’s when they make that brief flight you get the best chance to see the bird.
It has been estimated that the numbers of Cetti’s warblers in Britain doubles every four to seven years, for this is one of the most successful of colonists, helped, no doubt, by our milder winters caused by climate change. Across western Europe the population has also increased four-fold since 1990.
A Nightingale singing in Suffolk Wood. Once a common bird throughout the county, it has undergone a widespread decline in recent years
In contrast to the success of the Cetti’s Warbler, the Nightingale’s population in England has been declining at an alarming rate during the same period. Placed on the Birds of Conservation Concern’s Red List in 2015, the Nightingale has not only declined in number as a breeding bird in the UK (-90% between 1967 and 2022), but it has also vanished from many of the areas where it was once commonly found.
It’s generally thought that habitat loss has been the main problem, as the birds have suffered from a reduction in suitable breeding sites. Scrubby woodland, a favoured breeding habitat, has been lost through increased development or degradation, partly as a result of an increase in deer populations. However, according to a recent study by the BTO, the Nightingale’s misfortune is not solely based on issues occurring in its traditional UK breeding areas. BTO scientists have discovered, through the use of tiny geolocators, that British-breeding Nightingales spend the winter months isolated from other European Nightingales, in a specific, small region in and around The Gambia, West Africa. This means that this already declining population is at greater risk from deteriorating conditions in these winter quarters, through such threats as prolonged drought and loss of habitat.
Nightingales that have been tracked nesting elsewhere in Europe spend their non-breeding season in different, much broader, areas of West Africa, and are therefore less severely impacted overall by highly localised changes. We now know that British-breeding Nightingales rarely mix with other European populations while on the wintering grounds. The BTO hopes that advances in technology, through increasingly small and accurate tracking devices, will allow scientists to discover to what extent this phenomenon is widespread among other highly migratory species or restricted to certain species such as Nightingales.
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