The signature bird of the landscape this afternoon, whether you're walking alongside the canal or through suburban streets, is the alarmed Blackbird, suddenly swooping low across the path with, what the Witherby Handbook of British Birds describes as a low 'tchook, tchook, tchook, thchook.'
When startled, flies off with characteristic 'alarm rattle', a sudden 'hysterical' shrill, screaming chatter, of well-defined pattern, though subject to much modulation and variation in detail; commonly, but not necessarily, prefaced and ended with 'tchook' notes so that typical version might be rendered 'tchook, tchook, tchook-a, tchewee, tcheweechweechweechewee,chwee, tchook, tchook.'
A Sparrowhawk gives one some excuse for alarm. It has been sitting hunched up on a power line alongside the canal, rocking gently as it keeps balance in the cool wind. When it takes flight the blackbird breaks cover from the hawthorns by the towpath.