A radio tracking study of post‐fledging mortality and movements of Tawny Owls in Argyll

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Abstract
The post‐fledging mortality and behaviour of Tawny Owls was investigated in an upland conifer forest in Argyll, in a year of poor food supply. Twelve unsexed juvenile and 6 adult female owls were fitted with back‐mounted radios. Eleven (91.7%) of the juveniles died between fledging and independence. Deaths occurred in two peaks, initially in the period immediately following fledging when they were vulnerable to mammalian predators, and later on when they died mostly of starvation. While dependent on their parents the corrected home range size of the juveniles varied from 0.8 to 3.5 ha. Two broods showed sudden movements of 400–500 m from coniferous habitat around the nest site to predominantly broadleaved areas. The one juvenile that successfully left its parents territory did so 81–86 days after fledging. These results are discussed in relation to the method of radio tracking used.