Yesterday I visited Walthamstow Reservoirs in London (Canary Wharf towers just visible in the photo below) for more sound recording. Of most interest was a male Cuckoo uttering the familiar sound of spring. At the end of one bout of singing, a female gave the less often heard rippling or bubbling call (see first sonogram below) and the male immediately flew off in pursuit of it as it flew across one of the large water-filled basins to a wooded island. There are a number of possible hosts in this area though Reed Warbler or Dunnock could be the most likely. Also below are sonograms showing the trilling territorial voice of the Little Grebe (a chattering Reed Warbler also present on the recording) and some high-pitched social screams from a Swift.