Morphometric studies of a population of blue and great tits

Abstract

Weights of Blue and Great Tits, known continuous residents from a study population in Kent, showed little variation between July and early April. First-year Blue Tits (both sexes) weighed about 11 g, adult males up to 0.5 g more, and adult females about 0.5 g less. Great Tits weighed between 18 and 19 g (females) and 19 to 20 g (males), with little detectable difference between adult and first-year birds. In the breeding season, females ofboth species increased sharply in weight in the fortnight prior to the laying of the first egg-on average by 26% in Blue Tits and 18% in Great Tits. In both species, some females increased by between 30and 40%. High weights were maintained until shortly before hatching, and weights had returned to normal by fledging. During the period of most rapid increase in the female, male weights fell, due, it is suggested, to the strain of courtship feeding when the male gathers much of the female’s food requirements. Mean wing-lengths of birds of known age and sex from the same population ranged from, in the Blue Tit, 61 and 63.2 mm for first-year females and males, to 62.5 and 65.3 for adult females and males. For the Great Tit, first-year females and males’ mean wing-lengths were, respectively, 72.2 and 75.2 mm, and adults 72.8 and 76.4 mm. © 1977 Taylor & Francis Group, LLC.