Egg size as a predictor of nutrient composition of eggs and neonates of Canada Geese (Branta canadensis interior) and Lesser Snow Geese (Chen caerulescens caerulescens)

Abstract

Fresh and pipped eggs were collected to provide data on nutrient composition of eggs and neonates, respectively, of Canada Geese (Branta canadensis interior) and Lesser Snow Geese (Chen caerulescens caerulescens). We sought to determine how well a commonly used and simple index like estimated egg volume or "egg size" predicted egg composition and neonate characteristics including body composition, structural size, and digestive-organ mass. For both species, egg constituents were positively correlated with egg size, but relations for Canada Geese consistently had higher coefficients of determination than did those for Lesser Snow Geese. These differences suggest that there is more among-female variation in nutrient composition of Lesser Snow goose eggs relative to Canada Goose eggs. Most neonatal nutrient constituents were positively correlated with egg size in both species, but the relations between nutrient constituents and egg size were consistently stronger in Lesser Snow Geese than in Canada Geese. Several measures of structural size of neonates were positively correlated with egg size in both species, but egg size was a better predictor of neonate size for Lesser Snow Geese than for Canada Geese. Egg size was a relatively poor predictor of digestive-organ mass for both species. We hypothesize that the stronger relations between neonate quality and egg size in Lesser Snow Geese are a reflection of greater stabilizing selection for embryonic metabolic rates in species that nest at high latitudes and have a short incubation period. The fact that nutrient constituents of eggs were more strongly related to egg size than were the analogous constituents of neonates suggests that variation in metabolic rates of embryos limits the utility of egg size as an accurate and precise predictor of nutrient constituents in the two study species, but especially in Canada Geese.