Changes in organ size and nutrient reserves of arctic terns (Sterna paradisaea) breeding near a High Arctic polynya

Abstract

The arctic tern (Sterna paradisaea) is a ubiquitous migratory seabird of the High Arctic, currently thought to be in decline in most of the circumpolar world, but surprisingly little is known of its biology at high latitudes. We studied organ size and nutrient reserves of arctic terns breeding beside a High Arctic polynya in Nunavut, Canada, from their arrival at the colony into the chickrearing period. Both males and females had a decrease in gizzard size through breeding, with gizzard mass during chick-rearing 39 percent lower than on arrival at the breeding grounds. Through the duration of the breeding season, heart, liver, and small intestine showed little change, but females had higher fat and protein stores than males. Terns from this colony likely have increasing fat levels and high body condition due to proximity to a highly productive polynya, where terns appear to gain more energy than they expend during foraging trips. This suggests that though terns at this colony may be near the northern limit of their range, local conditions have a strong impact on organ and nutrient reserve dynamics of these arctic seabirds.