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Report on Chatham Island Shag tracking and testing of downloadable GPS devices Aug 2025 (PDF, 481K)

Summary

Five Chatham Island shags from a breeding colony located on the south-east corner of Rēkohu/Wharekauri/Chatham Island had their movements tracked using Bluetooth-enabled GPS devices during their pre-laying period of August 2025 in a project led by Mike Bell (Toroa Consulting; funded by DOC).

The devices were able to have tracking data downloaded remotely via Bluetooth connection to a mobile phone. For species that return often to colonies or roost sites, allowing for data to be downloaded regularly, they offer a cheaper alternative to satellite-based GPS devices.

The GPS trackers performed well, with data successfully downloaded through a mobile app at distances of up to 80 m. Some limitations were identified, including the need for reliable mobile phone coverage and a clear line of sight between the phone and the device. However, these issues can be reduced by carefully choosing the location of field sites and considering colony topography.

This study also provides the first tracking data for Chatham Island shags. The tracked birds stayed relatively close to their colony, typically foraging within 5 to 15 kilometres, and repeatedly returned to the same feeding areas. These behaviours along with their estimated dive depths are similar to those recorded for other blue-eyed shag species.

The study also found that breeding birds sometimes roosted at other breeding colonies. This is the first time this behaviour has been recorded in blue-eyed shags and may indicate that birds from different colonies use some of the same feeding areas.

Publication information

Bell, M. 2026. Chatham Island Shag tracking, and testing Bluetooth downloadable GPS devices. Report prepared by Toroa Consulting for the Department of Conservation. 9 p.