Atlantic Puffin (Fratercula arctica) chick diet and reproductive performance at colonies with high and low capelin (Mallotus villosus) abundance

We compared nestling diet and growth, breeding phenology, breeding success, and adult mass of Atlantic Puffins (Fratercula arctica) between two seabird colonies adjacent to ocean habitat with presumed high and low capelin (Mallotus villosus) abundance in 1996–1998. We hypothesized that puffins at their colony at Gannet Islands, Labrador, where capelin were scarce, would exhibit lower reproductive performance than at Gull Island, Witless Bay, where capelin were abundant. Historically, capelin comprised approximately 60%–95% of the chick diet biomass at both colonies. In the late 1990s, puffin chicks at the Gannet Islands received 3%–24% capelin (by mass), which was 39%–97% less than was received at Gull Island. Postlarval sandlance (Ammodytes sp.) comprised up to 49% (by mass) of the chick diet at the Gannet Islands. Hatching success and fledge success estimates at the Gannet Islands in 1997–1998 were statistically similar to those at Gull Island in 1998. Fledge mass (expressed as percentage of adult mass) was similar between Gannet Islands (69%) and Gull Island (68%). The high interyear variability in chick diet at both colonies and the low variation in breeding performance during our study suggest that Atlantic Puffins in Labrador are resilient to large-scale prey-base changes.