whole-todd-thesis-2012.pdf (4.46 MB)
Ecology and habitat of a threatened nocturnal bird, the Tasmanian masked owl
thesisposted on 2023-05-26, 01:59 authored by Todd, MK
Rare species are often those most in need of conservation measures and yet they are often the least well known and most difficult subjects for scientific research. The methods frequently applied when researching species ecology are often not feasible with rare species. This study investigates the ways in which habitat influences the ecology and distribution of a rare, threatened nocturnal bird, the Tasmanian Masked Owl (Tyto novaehollandiae castanops) using mostly indirect methods. The results provide insight into the value of indirect methods in determining habitat surrogates that may be used in conservation planning for rare and threatened species. Diet of owls in different habitats was determined using analysis of regurgitated pellets and a synthesis of previously published data. It was found that while the owl has a wide range of potential prey species, owls focus on particular prey species in different areas. Introduced species, particularly rodents, made up a large proportion of the diet at most sites. Sites that had little native forest contained low percentages of native species in the diet. Calling behaviour was explored using recordings of owls obtained during call playback surveys and via automatic recording devices set at roost sites. The screech call of the Tasmanian Masked Owl was found to be deeper and to reach higher frequencies than the Australian Masked Owl (T. n. novaehollandiae). Calls were shown to have the potential to discriminate between age, sex and potentially individuals. The occurrence of the owl throughout its potential range in forested areas of Tasmania was investigated using call playback surveys. Occupancy probability modeling (presence-absence data) was used to calculate the detectability of the Tasmanian Masked Owl in call playback surveys and to define habitat and landscape features that best predict owl presence. Wind (negative) and air temperature (positive) were found to have the most influence on Tasmanian Masked Owl detectability, while low elevation, mature dry eucalypt forest was determined to be the best predictor of occupancy. The best occupancy probability model was used to create habitat quality map. The habitat quality map was compared with maps created using presence only records and maximum entropy models. There was broad similarity in the maps although the habitat quality map was more detailed. The occupancy probability methods will be of value for the study of habitat preferences of a wide range of cryptic, and/ or rare species. The survey methodology used would vary depending on the species of interest, but the statistical framework behind the models would remain applicable. The call analysis methods and the diet analysis methods are applicable to studies of other owl species. By combining the results obtained using the indirect techniques with knowledge of owl ecology from the literature, possible causes of the estimated small population size for the Tasmanian Masked Owl were explored. A range of habitat factors can affect the Tasmanian Masked Owl, including nesting and roosting habitat, elevation and mature dry eucalypt forest. Prey availability (abundance and accessibility) is likely to be the ultimate factor responsible for the distribution and abundance of Tasmanian Masked Owls and it probably is reflected in the distribution of low elevation, mature dry eucalypt forest in Tasmania.
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