Biometrics and primary moult of non‐breeding kittiwakes rissa tridactyla in liverpool bay, england

Abstract

During 1977 to 1984 a total of 762 non‐breeding Kittiwakes were trapped between April and September at a site on Liverpool Bay, England. Ageing criteria are described. Mean wing‐length and bill‐depth increased with age, but only measurements of first‐year birds were significantly different from other age classes. Neither bill‐length or tarsus‐length showed any variation with age. Mean weights of first‐year birds tended to be lower than those of older birds and there was evidence of body weight loss during the summer, possibly due to the stress caused by the progression of moult. Median primary moult scores of first‐ and second‐year birds were significantly higher than those of older individuals. Primary moult takes place between May and October but estimation of it's duration were unreliable due to the restricted range of data, with estimates varying between 106–187 days. A figure of ca. 130 days is suggested. The influence of age, sex, geographical origin and seasonal variation on body size are discussed. © 1994 Taylor & Francis Group, LLC.