Effect of nest-site location on reproductive success of red-throated loons Gavia stellata

The Red-throated Loon (Gavia stellata) nests on the shores of freshwater ponds of the Arctic tundra and forages in nearby marine waters. We examined the effects of distance of the nest from foraging waters and of microclimate at the nest site on the loon’s reproductive success. As distance from the ocean increased, both density and nesting success decreased. Although hatching success did not vary with distance, success in rearing both chicks was significantly lower at distances greater than 9 km from the ocean. Loons with nests further from the ocean fed chicks less often and spent more time on foraging flights than did loons nesting within 9 km of the ocean. Brood reduction in nests far from the ocean presumably resulted from nestling starvation, and possibly also from higher predation due to less effective nest defense. We suggest that the higher density of breeding loons in areas near the ocean reflects preference of these birds for nesting grounds that are closer to their foraging areas. Microclimatic conditions also influenced reproductive success. In areas available for nesting earlier in the year, the loons initiated nesting earlier, but the probability of their reproductive failure due to predation was higher. However, successful pairs in these areas raised larger broods (two chicks) more often than those in areas where birds started breeding later.

Christine Eberl and Jaroslav Picman, Auk: Vol. 110, No. 3