Uttley J.D. (1992) Food-supply and allocation of parental effort in Arctic Terns Sterna paradisaea. ARDEA 80 (1): 83-91

Male and female reproductive strategies differ, resulting in differences between the time and energy budgets of the sexes during reproduction. Consequently, the responses of the sexes to environmental conditions during breeding may not be the same. Recently Arctic Terns Sterna paradisaea breeding in Shetland have experienced reduced food availability, whereas those breeding in Orkney have not. Male and female Arctic Terns in Orkney contribute equally to incubation, but males brood young chicks (less than 10 days old) less and feed them more, than females do. Males in Shetland contribute less than females to incubation during laying, but the brooding and feeding effort of the two sexes are equal when caring for young chicks, due to a switch from brooding to foraging by females. The changes in allocation of effort during laying may allow the laying of a larger and better quality clutch than would otherwise be possible, through reducing female energy expenditure and increasing courtship feeding. Changes later in the breeding season may increase potential chick survival or be a manifestation of reduced reproductive effort and increased somatic effort.