REED, W.R.; CLARK, M.E.; BENOY, G.; North Dakota State University; North Dakota State University; University of Calgary: Parental and environmental factors generating variation in growth rates in free-living birds

Variation in growth rates during the juvenile period can have a large influence on variation in adult morphological, behavioral and life-history characteristics. In birds, the mechanisms that generate and maintain variation in juvenile growth rates can be analyzed in context of pre-hatching and post-hatching factors. We distinguished between the relative contributions of these two factors on growth rates of juvenile American coots by randomly fostering chicks among nests at the time of hatch. Pre-hatching factors that influence juvenile growth rates included a combination of genetic and maternal effects present in eggs, as well as whether an egg was laid in the first or second half of its clutch. Eggs laid earlier in the clutch had slightly higher growth rates relative to eggs laid later in the clutch. This result corroborates the hypothesis that females allocate resources unequally among offspring in a way that exacerbates the effects of hatching asynchrony. Post-hatching factors that influence growth rates included the foster nest in which a bird was raised. These effects reflect the extent to which habitat quality and efficacy of parental care influence growth rates.