Ageing and sexing Marsh Tits Poecile palustris using wing length and moult

Ageing and sexing Marsh Tits Poecile palustris presents some difficulties for ringers. Wing length has previously been found to be useful for sexing English Marsh Tits, although the replacement of all juvenile rectrices and greater coverts by first‐year birds made ageing difficult. We examined Marsh Tits of known age and sex and found that 93.5% of birds could be sexed correctly using wing lengths of ≤ 62 mm for females and ≥ 63 mm for males. Wing length was also an indicator of age: many first‐years had shorter wings, but most also retained some juvenile rectrices and greater coverts after the post‐juvenile moult, and could be readily aged using these features. We found a primary moult period of 67 days for adult Marsh Tits, with a mean onset of 27 May.