BOBOLINK EGG MASS VARIABILITY AND NESTLING GROWTH PATTERNS

The Bobolink (Dolichonyx oryzivorus) is an obligate grassland species that is declining throughout its range in North America. There are few data available on Bobolink eggs and nestlings; this information is necessary for conservation planning efforts. Egg mass was recorded for 175 eggs from 37 nests in Quebec and eastern Ontario in 2006-2007. Hatching asynchrony was evident with high between-clutch variation in egg mass. Egg mass did not differ with clutch size. Nest initiation date was positively correlated with smallest egg size and negatively correlated with within-clutch egg mass deviation. Nestling wing length, tarsus length, and mass were measured for 166 nestlings ranging from 2 to 10 days of age. Bobolink nestlings fledged below adult size and mass, achieving 87.7 +/- 2.3%, 67.6 +/- 1.5%, and 55.1 +/- 0.4% of breeding adult tarsus length, mass, and wing length (+/- SE), respectively.