Parental age and offspring ectoparasite load in European Shags Stictocarbo aristotelis

European Shag (Phalacrocorax aristotelis) Science Article 4


While age related improvements in breeding success have been reported in many avian species, the underlying mechanisms are not well understood. Ectoparasite load can have a significant deleterious effect on many aspects of host fitness. If younger breeders carry high parasite loads, and this has a detrimental effect on their chicks, this could contribute to the poorer breeding success of younger pairs. We measured loads of the conspicuous ectoparasitic louse Eidemanniella pellucida (Phthiraptera: Amblycera) on chicks reared by young and older breeding Shags Stictocarbo aristotelis. Since young Shags breed relatively late in the season, and lay smaller eggs, we used a cross-fostering procedure to control for environmental and egg quality effects on chick louse loads. We found that, independent of breeding period and whether the chicks hatched from eggs laid by young or older birds, broods raised by young pairs carried a significantly higher louse load than those raised by older pairs. In our data set, we could not detect an effect of louse load on offspring growth and survival when controlling for parental age in the statistical analysis. However, to examine this fully, an experimental manipulation would be required to break the otherwise close relationship between parental age and louse numbers

Daunt F., Monaghan P., Wanless S. & Harris M.P., ARDEA 89 (3): 449-455

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