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The role of prey quality in rhinoceros auklet (Cerorhinca monocerata) productivity Beaubier, Jessica


While shifts in the species composition of seabird nestling diets are generally well described, their energetic implications for nestlings are poorly understood due to a lack of information on relative prey quality. I investigated how prey quality related to interannual differences in rhinoceros auklet reproductive success at Triangle Island, British Columbia. I first estimated the energy density and proximate composition of the 4 main prey types (Pacific sand lance (Ammodytes hexapterus), Pacific saury (Cololabis saira), juvenile rockfish species (Sebastes spp.), and juvenile salmon (Oncorhynchus spp.) fed to rhinoceros auklet nestlings at Triangle Island. I then developed models of prey energy content and used them to estimate average energy content and quality of rhinoceros auklet nestling meals in two years of contrasting diets. I then tested to see if diet differences correlated with differences in chick growth and fledging characteristics. Prey types varied in energy density, both within and between species, which discounts using relative meal biomass as a proxy for relative meal energy content. Both mass and energy of nestling meals were lower in 2003 than in 2004 and varied non-linearly over the course of each breeding season. Average diet quality (kJ/g) did not vary between years and interannual differences in energy were driven by differences in average meal mass. Differences in prey availability may have led to large differences in productivity between years, but primarily by affecting hatching success rather than chick growth. Of nestling variables measured, only tarsus length varied between years: 2003 tarsi at fledge were shorter than those of 2004. Prey availability was likely more important than prey quality in driving annual production during these two years of study at Triangle Island.

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