Variations in Growth of Roseate Tern Chicks: II. Early Growth as an Index of Parental Quality

We measured growth of Roseate Tern (Sterna dougallii) chicks at a colony in Connecticut in 10 successive years, 1987-1996. Data on body mass during the first 3-4 days of life were fitted to a quadratic regression model, yielding three parameters of early growth for each of 1,551 chicks: mass at hatching, linear growth, and quadratic growth. First chicks in each brood (A-chicks) exceeded second chicks (B-chicks) in each of the three growth parameters; A-chicks from broods of two grew faster during the first 3 days than single chicks. The three parameters of early growth depended upon egg mass, hatch order, hatch date, and year, but not on parental age after controlling for effects of the other variables. The linear and quadratic growth parameters were negatively correlated. Subsequent growth and survival of chicks were predicted by all three parameters of early growth. After controlling for effects of early growth, none of the other variables measured (hatch date, egg mass, parental age, hatching asynchrony, female-female pairing, or trapping) contributed significantly to explaining later growth or survival. Year effects were substantial in only 2 of the 10 years of study. Individual pairs were consistent in performance (as indexed by early growth) in successive years. These results suggest that growth and survival of Roseate Tern chicks are determined primarily by parental quality; much of the information about parental quality is expressed by the time the eggs are laid, and most of it is expressed by the time the chicks are three days old.