Separating British Marsh Tits Poecile palustris and Willow Tits P. montana using a new feature trialled in an online survey

Confident separation of Marsh Tits and Willow Tits remains a challenge in Britain due to the similar appearance of the local races of both species. Several criteria are available to assist the identification of birds in the hand, but none is completely diagnostic and most are invalid for young juvenile birds. Due to the continued decline in abundance of both species, however, it is becoming increasingly difficult to trial new identification criteria in the field, as very few ringers are catching sufficient numbers of either species. This paper describes the results of an online survey that was used to test a proposed new identification feature for separating the two species, based on differences in the pattern of colour contrast on the greater covert feathers. The online survey was effective in recruiting a sufficient sample of ringers, of varying experience, who were asked to identify images of Marsh Tits or Willow Tits based only on features of the greater coverts that had been demonstrated using training images. On average, each ringer identified 82% of the 18 images correctly, and each image was identified correctly by an average 84% of the 140 ringers. The pattern of the greater coverts is therefore recommended as an additional, complementary criterion for separating Marsh Tits from Willow Tits. Online surveys are also recommended as an efficient platform for the trialling of identification features within the ringing community.