Birth-site habitat selection in gray seals (Halichoerus grypus): Effects of maternal age and parity and association with offspring weaning mass

Selection of birth-site habitat can have important effects on the reproductive success of females and the survival of offspring. We studied birth-site habitat selection by gray seals (Halichoerus grypus) on Sable Island, Nova Scotia, and the associated effect on offspring body mass at weaning. We identified a mosaic of eight habitats using orthorectified imagery from a photographic aerial survey conducted in January 2016. The distribution of birth sites of 814 females in 2014-2016 compared to the available habitat in 2016 provided evidence for positive selection of habitats that were not subject to tidal influence or flooding. The habitat selected for parturition varied with both female age and parity. Younger and inexperienced females were more likely to pup in beach habitat, while older and more experienced females were more commonly found inland and on vegetated dunes. Longitudinal data from 540 females observed between 2006 and 2016 revealed moderate repeatability of birth-site habitat selection (r = 0.269, 95% CI [0.236-0.326]). Pups born in inland sand habitat that did not flood averaged 1.5 kg heavier (similar to 2%) at weaning than those born on tidally influenced beach habitat. Overall, birth-site habitat selection was associated with small effects on offspring body mass at weaning.