Studies on the breeding biology of arctic terns (sterna paradisaea) (=S macrura) with special reference to age

Abstract

The breeding biology of Arctic Terns (Sterna paradisaea) (=S.macrura) was studied on the Farne Islands, off the coast of Northumberland, from 1965 to 1968. Clutches of two predominated in 1966 and 1967 but the second eggs were significantly smaller than the first. Starling (Sturnus vulgaris) predation accounted for most of the egg loss, and in 1966 and 1967 approximately 45% of all eggs laid, hatched successfully. Chicks were weighed daily and showed a steady increase in weight from the third to the fourteenth day. Laboratory rearing of chicks showed that these required 26.2g of fish per day to maintain a daily growth rate of 6.8g. The low chick mortality in 1967 (20. 9%) may have been due to an abundance of food. In other years chick mortality was approximately 40%, with a significantly higher mortality of second chicks. It was only possible to determine the age of individual adult birds from the ringing records of previous years. Ringed adults were caught and from the survival of colour ringed birds, the annual mortality was found to be 13%. A life table was constructed and gave an annual mortality of 15.1% with an expectation of life of 4.5 years. Members of a pair were likely to be of a similar age. Birds over ten years old returned to the colony first and produced more young than any other age group, in spite of having a smaller clutch and egg size than birds of six to eight years. Three year olds were the least successful age group. In 1968 a bloom of din of lagellates, or red tide, led to the death of approximately 1% of the breeding terns, and breeding success was very low due to increased egg predation by Starlings and chick predation by gulls, which was probably associated with the loss of the advantages of colonial breeding.