SURVEYS OF LARGE FOREST OWLS IN NORTHERN NEW SOUTH WALES: METHODOLOGY, CALLING BEHAVIOUR AND OWL RESPONSES
| Posted: |
08/08/2021 |
| Author(s): |
S. J. S. Debus |
Field surveys of large owls were undertaken in coastal, escarpment and tableland forests of
north-east New South Wales in 1990-92. A combination of listening, playback of taped calls and
spotlighting was used at 401 sites. Of these, 354 sites were surveyed at least twice each. Powerful
Owls
Ninox strenua were recorded at 76 sites (19%), Sooty Owls
Tyto tenebricosa at 74 sites (18%)
and Masked Owls
Tyto novaehollandiae at 35 sites (9%). Owls called spontaneously throughout the
night. but particularly in the early evening and before dawn. The effects of moon visibility and cloud
cover on spontaneous calling rates were not significant. Precipitation and wind were the two most
important factors affecting owl detectability: owls were vocal on calm, dry nights but were not heard
on nights of strong wind or heavy rain. Playback more than doubled the detection rate for all species;
owls responded with distant calls. approached and called from a concealed or unconcealed perch, or
occasionally approached silently. From a subsample of 48 sites surveyed five times each, the
probability of detecting owls on a single visit was 26 per cent for Powerful Owl, 21 per cent for Sooty
Owl and 20 per cent for Masked Owl. The number of visits required in order to determine owl presence
or absence at a given site, with 90 per cent confidence, is seven for Powerful Owl, eight for Sooty Owl
and nine for Masked Owl. For greater than 50 per cent probability of detection, the required number
of visits per site is three for Powerful and Sooty Owls and four for Masked Owl.
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