The effect of egg harvesting on the growth of chicks and breeding success of the Shag Phalacrocorax aristotelis and the Kittiwake Rissa tridactyla on Bleiksøy, North Norway

Abstract

Eggs of Shags Phalacrocorax aristotelis and Kittiwakes Rissa tridactyla are harvested annually for human consumption on Bleiksøy, North Norway until 1 June. The continual experimental removal of 19 Shag and 30 Kittiwake clutches until the same date in 1986 had little effect on the growth of chicks and the breeding success of thepairs involved. The size of the Kittiwake replacement clutches was smaller than the first clutches, and the Shag replacement eggs were smaller than the first eggs . There was no difference in the hatching success (no. eggs hatched/clutch laid) of the control and replacement clutches of either species. The growth rates of chicks hatched from control and replacement clutches were similar forboth species, as was theoverallfledging success of both categories of Kittiwake chick. Egg harvesting did not seem to have any short-term effect on either species, probably because it was limited to the first half of the laying season.