Breeding biology of Arctic terns (Sterna paradisaea) in the Canadian High Arctic

The Arctic tern (Sterna paradisaea) is a well-nown polar seabird which breeds around the circumpolar Arctic, and which undertakes the longest known annual migration of any organism. Despite its familiarity, there is little information on its breeding biology in the High Arctic, an important baseline against which future studies of climate change impacts on northern wildlife can be compared. We studied the breeding biology of Arctic terns in the Canadian High Arctic during five field seasons, and compared this to breeding biology of terns from more southern parts of its range. Because our field site was beside a productive polynya, we expected that reproductive metrics for terns nesting there would be relatively high. However, mean clutch size (1.7 eggs), mean egg size (40.2 mm x 29.0 mm), mean nest initiation dates (6 July) were similar to Arctic terns breeding elsewhere. With our data, we could not assess the independent effects of predation pressure, poor weather or low food supplies, but two years with low tern reproduction were also years with low adult body mass and low clutch size (indicating poor food supplies), as well as low hatching success and high nest abandonment (possibly due to high predation pressure).