Population-level distribution strategies, such as migration, nomadism or residency, form often as a result of spatio-temporal resource dynamics. While commonly a species will adopt a single strategy across its range, occasionally multiple strategies can be observed. In Australia, the eastern grass owl Tyto longimembris is considered nomadic over most of its range. However, resident populations have been reported along the eastern coastal zone. We collected and analysed regurgitated pellets of a coastal resident population across three seasons in a single year. We compared these data with the availability of prey in the field to investigate whether resource predictability and foraging behaviour facilitate shifts between nomadism and residency. Many of the prey species consumed by the resident population display little spatial or temporal variation compared with prey consumed by nomadic populations. Temporal differences were observed in the diet with the main prey species (house mouse) declining from 88.9% in summer to 66.7% in winter and 40.0% in spring (P<0.01). Conversely, bird and rat consumption increased across the three seasons (16.3, 28.6 and 34.0% for birds, P=0.08; and 15.0, 33.3 and 75.0% for rats, P<0.01; for summer, winter and spring, respectively). Trapping resulted in the capture of house mouse Mus domesticus only, which declined significantly from the first half to the second half of the year (P<0.01). These data indicate that the eastern grass owl in the coastal zone is a specialist predator of small rodents, but will broaden its diet to feed opportunistically on a range of other species when the preferred prey are less abundant. We conclude that the capacity to switch between specialized and opportunistic predation, combined with prey that are spatially and temporally more predictable, facilitates shifts between nomadism and residency in the eastern grass owl.
|Number of pages||6|
|Journal||Journal of Zoology|
|Publication status||Published - Aug 2011|