In mid April there was a mob arrival of our common woodland warblers. At present Blackcaps are singing across our project area in shrubby gardens and hedge rows. Our recent CNHS visit to Coldham’s Common found Blackcaps singing their rich 6 second warble in the bushes every 100 metres and Chiffchaffs singing their repetitive “chiff chaff” song also every 100 metres between the Blackcaps. Occasionally there is a Willow Warbler with its “beautiful descending sequence” (Martin Walters, Cambridge Independent April 2017); most are probably passage birds moving north. They can turn up anywhere and two were recently seen and heard in the street trees in Ditton Fields.
Chiffs and Willow Warblers are both small, very similar unobtrusive greenish warblers; Chiffs are usually duller with darker legs with a nervous habit of flicking their tail downwards. Just occasionally there is a “wiffwaff” ! These are Willow Warblers but with “chiff chaff” inserted into their song. There is one on Coldham’s Common at present (follow the path from Newmarket Road past the football stadium to where the bushes cross the path and on the left – in the bushes behind the allotments). This Willow Warbler has the “chiff chaff” notes at the end of its song; a bird at Little Paxton Local Nature Reserve near St Neots has clear “chiff chaff” notes at the beginning of its song. Both birds show the plumage characters of typical Willow Warblers.
Tony Fulford, Behavioural Ecology Group,University of Cambridge is studying these Willow Warblers with aberrant songs to see if it helps teach us why birds sing. If you come across one such bird please contact tonyfulford@gmail.com with location details.
Willow Warbler Chiffchaff
In the same area on Coldham’s Common is a much less common marshland warbler – a Cetti’s Warbler. These birds are resident; they first bred at Radipole Lake near Weymouth in the late 1960’s but have now spread north to Lancashire and can survive our warmer winters. They look like Reed Warblers and nest in similar habitats. Reed Warblers are parasitised by Cuckoos but Cetti’s Warblers lay red eggs which Cuckoos cannot yet mimic – they have beaten the Cuckoo trap (see the excellent book Cuckoo Cheating by Nature by Nick Davies, Professor of Behavioural Ecology, University of Cambridge). Cetti’s Warblers are birds of dense reedy cover and are difficult to see but they have an unmistakable explosive song – a loud “chet chet cherweoweeoo”!
Although they are mainly resident – Cetti’s Warblers have distinctive stumpy short wings not designed for long distance migration unlike Reed Warblers – but a Cetti’s Warbler ringed at the Great Fen near Peterborough was re-caught at Leighton Moss in Lancashire.
Look out for Swifts – they are here!
Bob Jarman 6th May 2017