Breeding ecology of Artic Tern (Sterna paradisaea) and Common Tern (Sterna Hirundo)

Abstract

Seabird breeding populations have been experiencing change over the last 40 years with low reproductive success being associated with poor foraging conditions. A comparison of the breeding ecology of Arctic and Common Terns showed significant differences in reproductive strategy and output associated with differences in their sensitivities to changing conditions. Both clutch size and productivity were consistently lower in Arctic Terns than Common Terns. Chicks of both species hatched asynchronously with mortality increasing down the brood hierarchy. Younger sibling survival was impacted both by seasonal conditions and by elder sibling survival, although to varying degrees depending on species and hatching order. Arctic Terns foraged at a higher rate but on less energy rich prey and on a less varied diet. Both species increased provisioning and decreased parental attendance at the nest as chicks grew older, corresponding with the changes in chicks’ thermoregulatory abilities and energy requirements. Provisioning of chicks was primarily increased by selection of higher energy prey rather than through increased provisioning rate. Diurnal rhythms in either provisioning rate or diet were seen in both species, primarily associated with changing behaviour of prey fish. Temperature and precipitation affected provisioning, but adults maintained energy delivery to chicks. Increase in wind speed negatively impacted chick provisioning despite increased foraging effort. Chick mortality was linked to weather and feeding conditions, with high mortality linked to windy conditions and low provisioning. Yearly differences in productivity and chick mortality were associated with provisioning, and low parental attendance indicated poor foraging conditions. The reproductive output of both species is sensitive to declining foraging conditions and increased severity of weather conditions. The data implies that the sensitivity of Arctic Terns is greater than that of Common Terns, and that conditions around Coquet Island are sub-optimal for Arctic Tern breeding.