Separation of Marsh Tit Poecile palustris from Willow Tit Poecile montana using a bill criterion

are difficult to separate on visual appearance, with a large degree of overlap of identification features (Perrins 1979, Scott 1999). This problem is particularly acute in the British races, P. p. dresseri and P. m. kleinschmidti, with birds in juvenile plumage considered to be essentially inseparable (Perrins 1979). Both the Marsh Tit and Willow Tit are on the ‘Red List ’ of birds of serious conservation concern due to the significant decline in the British population of both species since the 1970s (Baillie et al 2007). Similar declines have been detected elsewhere in Europe, although the cause or causes remain unknown (BirdLife International 2004, PECBMS 2007). The evidence from Britain is that the decline of the Willow Tit has been more severe than that of the Marsh Tit (Baillie et al 2007), and differing factors may be at work (Siriwardena 2004, 2006). It i