The American White Pelican (Pelecanus erythrorhynchos) is an iconic waterbird breeding in the Prairie Pothole and Upper Midwest Regions of North America. Significant variation in recruitment occurs among years. However, mechanisms affecting recruitment, such as variation in size at hatching and chick growth, have not been quantified. In this study, size at hatching and growth rates of American White Pelican chicks were examined at Mash Lake, Minnesota, USA, during 2010–2012. On the day of hatch, the mass and lengths of tarsus, wing and culmen were recorded for the oldest chick in 2-egg nests. No difference was detected in skeletal size at hatching during 2010–2012, but mass of chicks was 11% lower in 2010 than in 2011. Growth rates for mass and wing did not differ between 2011 and 2012, but over 40% of the variation in absolute and instantaneous (relative) growth rates of tarsus was explained by year, with higher rates in 2011; in 2011, nest initiations were started later than other years. Little variation in size at hatching or growth rates were detected between years, but significant variation in size at hatching and growth rates were detected within season depending on the timing of hatch. No difference was detected in initial mass throughout the nesting season, but initial tarsus and wing length were shorter in chicks hatched later in the season in 2012. However, absolute and instantaneous growth rates for mass, tarsus and wing were greater for late-hatched chicks in 2012, potentially allowing late-hatched chicks to fledge at an earlier age.
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Vol. 40 • No. 3