Marchant, J. H / November 1984 – vol. 77, issue 11, pp 570–571 Recommended letter-code abbreviations for British birds. For over 20 years, members of the BTO have been using letter-codes to register birds seen on Common Birds Census visits. Various additions to the list of codes have been made over the years, notably in 1974 when a number of scarcer waterside birds were assigned codes for the purposes of the Waterways Bird Survey. The BTO/IWC Winter Atlas Proj... This article is only available to registered users.To read more, please log in or purchase a subscription.