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BCBC2020-24: Otago and Foveaux shags population census trials (PDF, 1,912 K)

Summary

Endemic to Southern New Zealand, Foveaux shag Leucocarbo stewartia and Otago shag Leucocarbo chalconotus are classified as threatened, but little is known of their populations’ status and trends to inform conservation management. The aim of this project was to identify current breeding sites and develop a suitable methodology for use in future breeding population census of Foveaux and Otago shag colonies, using two sites for each species.

To identify whether suitable aerial population census data for Foveaux and Otago shags can be obtained using a drone, we conducted animal disturbance trials and assessed the quality of imagery for counts. We also determined temporal colony attendance by installing trail cameras. Records of historic and contemporary breeding sites included ten Otago shag breeding sites and 15 Foveaux shag breeding sites. Future comprehensive surveys should include all 25 breeding sites in targeted visits to determine the population size of Otago and Foveaux shags. Animal response trials showed that drones can be flown slowly over Otago and Foveaux shags as low as 20 m without causing notable disturbance. Since this study only covered non-breeding and pre-breeding stages, overflights during the breeding season should first determine the drone flight height that causes minimal disturbance at that stage. Drone footage from 20 m flight height is of excellent quality for counting shag numbers in colonies.

To get the best estimate of numbers of breeding pairs, ground-truthing data that assesses nest contents must be collected to correct counts of apparently nesting shags from photographs. Camera monitoring during the non-breeding season showed clear diurnal patterns of colony attendance. Information from cameras deployed into the breeding season should provide nest survival rates, enabling correction of Foveaux and Otago shag population size estimates.