Increased house mouse (Mus musculus) abundance in wetlands in response to Typha sp. flowering: implications for understanding wetland occupancy patterns of the eastern grass owl (Tyto longimembris)

Abstract. Rises in abundance of a population in response to increased resources is often followed by a rise in predator abundance. The non-threatened eastern barn owl (Tyto alba delicatula) and the threatened eastern grass owl (Tyto longimembris) are predators that may have occupancy patterns linked with prey abundance. It is important to identify the resources that cause increases in primary prey items to further understanding of the ecology of these species. Here I test the hypothesis that grass seeds cause increased abundances of wetland-dwelling house mice (Mus musculus) in austral summer, and identify a wetland monocot that provides a food recourse to achieve this effect, as well as report eastern grass owl and barn owl observations. A 2.6 ha wetland area (on Kooragang Island, New South Wales) was surveyed almost weekly to quantify abundance of prey items from September to April for three years (2016–2019). Typha sp. (a monocot) had flowering periods that coincided with increases in house mouse observations (n = 90 in flowering, n = 2 in non-flowering), where 22% were detected feeding on Typha flowers/seeds or fleeing from flower stalks. Eastern grass owls were only observed during a Typha flowering period (n = 3). These observations confirmed the original hypothesis and led to the formulation of another hypothesis: wetland occupancy by eastern grass owls is influenced by Typha flowering. Future studies should aim to test this hypothesis and identify other wetland plants that provide an important food source for wetland-dwelling rodents.