Environmental and social factors affecting the excretion of intestinal parasite eggs in graylag geese

In group living vertebrates, patterns of parasite infection vary within and between populations because of environmental and social factors. In the present study, we investigated patterns of parasite product excretion in graylag geese, focusing on environmental (season and temperature), individual (sex and age), and social factors (pair-bond status, reproductive state, and rearing condition). From March 2008 to May 2010, we collected 3574 samples from 171 individuals and analyzed them for nematode eggs and coccidian oocysts. Fecal samples that were infected with nematode eggs were also positive for coccidian oocyst to a higher rate. Fecal samples of goose-raised geese were positive for nematode eggs more often than those of hand-raised geese. In parental birds, the number of goslings fledged had a positive influence on the percentage of samples positive for nematode eggs. The number of samples infected with coccidian oocysts decreased with age. In parent birds, the number of samples found to be positive for coccidian oocysts decreased during the parental season, and female bird samples were positive more often than those of males. In graylag goslings, the number of fecal samples with coccidian oocysts was influenced by the goslings’ age, with maximum excretion at 13 weeks. This is the first evidence to demonstrate an effect of a set of interacting environmental (e.g., season), individual (e.g., sex, age), and social (e.g., rearing condition, number of goslings fledged) factors on rate of parasite excretion in a socially complex bird. Our results suggest that socially stressful periods may have implications for individual health in graylag geese.