Brood size and food provisioning in Common Tern s Sterna hirundo an d Arctic Terns S . paradis a: consequences for chick growth

Food provisioning rates and chick growth rates of Common Te rns Sterna hirundo and Arctic Tems S. paradis a were studied in Northeast Engl and. Adult tems of both species fed large broods more frequently th an those containing fewer chicks . Energy supply per nestling declined slightly as brood size increased and as a result, chicks in large broods developed body mass at a slightly lower rate than those in small broods . Although brood size had no effect on fledging mass in either species, Common Te rn chicks from large broods reached fledging mass later than those in small broods . Despite significant effects of brood size, mass growth rate hierarchies did not occur within broods of either species and hatching position had no effect on the mass of fledglings . Brood size and hatching position had no effect on die rate at which chicks developed structurally or on final body size . These results suggest that flexibility of m ass growth rates in Arctic and Common Terns may act as a fine-tuning mechanism, allowing parents to increase their annual reproductive output through slower mass growth rates of chicks .

Robinson J.A . & K .C . Hamer 2000, Ardea 88(1) : 51-60