Seasonal dietary changes of Formosan mouse (Mus caroli) revealed by stable carbon and nitrogen isotopes

The Formosan mouse (Mus caroli) in Taiwan is an omnivore feeding on herbal seeds and invertebrates. We hypothesized that the feeding on invertebrates by the Formosan mouse would decline during winter when the abundance of invertebrates may decline. We used stable carbon and nitrogen isotope analysis of mouse hair samples to monitor the seasonal change of diet at a salt marsh in northern Taiwan between June 2005-May 2006. A multi-source mixing model showed that the invertebrates made up up to 74% diet of the Formosan mouse regardless of seasons, and the species was a secondary consumer around the year. It was probably because invertebrate biomass remained constant through seasons. However, the stable carbon isotope values indicated that during summer, when C4 plants produced a large number of seeds, C4 plant contributed more carbon source to Formosan mouse than in other seasons. We inferred that the seasonal shift in carbon source was due to the greater abundance of invertebrates feeding on C4 plants during summer.