Little is known of natural variation in the innate immune system of wild animals. Therefore we investigated if birds alter their innate immune system during demanding periods (e.g. moult) or changing environment (e.g. reduced pathogen loads) for the individual. For this purpose, blood was sampled of juvenile and adult wild barnacle geese during the breeding season on Spitsbergen, and tested for the ability to kill three different pathogens in vitro. Barnacle geese varied in their ability to kill the three pathogens but within individuals the killing of the different pathogens was not correlated. Goslings killed less Candida albicans than adults but did equal on killing Staphylococcus aureus and Escherichia coli. Goslings increased their killing ability only for E. coli during growth. For adults the response decreased with moult progress for S. aureus and E. coli but not for C. albicans. Adult females were better in killing the S. aureus than males during moult. Thus barnacle geese varied in their innate immune system with the different life stages. Birds may adapt their innate immune system according to changes in pathogen pressure and/or birds could have been allocating energy and nutrients away from the innate immune system to compensate for energy and nutrient demands of moult and growth. This suggests that the geese regulate and redistribute their uS to keep the immune system working at the lowest possible cost.