Stomach flushing does not affect apparent adult survival, chick hatching, or fledging success in yellow-eyed penguins (Megadyptes antipodes)

Stomach flushing has been used in diet studies of 17 of 18 species of penguins, and is commonly used to obtain diet samples from fish, reptiles, amphibians, mammals, and other bird species. However, a review of the literature indicates that there have been virtually no assessments of the impacts of stomach flushing. Stomach flushing has been used in four studies of yellow-eyed penguins (Megadyptes antipodes), with extensive investigations during 1984 to 1986, and 1990 to 1993. Using long-term data we compared yellow-eyed penguin adult resighting probability, productivity, and chick mass, between nests where adults were flushed, with those that were not. Flushed birds were less likely to be resighted than birds that were not flushed, although when the poor season of 1985/86 was removed, resighting rates were comparable between flushed and non-flushed birds. Hatching success and fledging success were unaffected by flushing, however, the mean mass of chicks was lower in nests where the combined number of stomach flushes for both parents exceeded four events. Our results imply that stomach flushing has no long-term effects on apparent adult survival or productivity, unless undertaken during a year of poor food availability. We recommend that future diet studies of yellow-eyed penguins that require using stomach flushing apply no more than four stomach flushing events per nest during breeding. The use of complementary biochemical techniques could reduce the need for stomach flushing of yellow-eyed penguins, however we advocate for the use of dietary analysis methods that are most appropriate to address important knowledge gaps.