Flesh-footed shearwater population monitoring and estimate 2023/24

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POP2021-04: Flesh-footed shearwater population monitoring and estimate: 2023/24 (PDF 5,226K) 

Summary

report covers the findings from the year of toanui/flesh-footed shearwater (Ardenna carneipes) research under Conservation Services Programme (CSP) project POP2021-04 for the 2023/2024 season, funded by Department of Conservation (DOC). Here we report on the ongoing population monitoring and population estimates of flesh-footed shearwaters on Ohinau and Mauimua/Lady Alice Islands, as well as tracking of adults for both islands and tracking of fledglings from Titi Island.

During the 2023/24 season WMIL monitored 263 and 291 study burrows on Ohinau Island and Lady Alice Island respectively. Of these 71.5% and 71.8% were breeding burrows for Ohinau and Lady Alice respectively. We were able to identify 61% of breeding birds in burrows on Ohinau Island and 86% of burrows on Lady Alice Island.

Determining breeding success was not a deliverable for this season. On Ohinau 5.1% of chicks, which have been banded since monitoring began, have been recaptured at the colony and on Lady Alice 11.8% of banded chicks have been recaptured.

Burrow transects were carried out on both Ohinau Island and Lady Alice Island to gather data for an updated population estimate for these islands. On Ohinau 116 transects, each aiming to cover 40m², were completed within eight different colonies on the island. We estimate that there are a total of 3,722 occupied breeding burrows (1,881 – 5,566, 95% CI) on Ohinau Island which is a decrease of 4.17% since 2018. On Lady Alice Island 323 transects were completed within nine colonies. We estimate that there are a total of 2,367 occupied breeding burrows (1,431-3,303, 95% CI) which is decrease of 26.4% since 2019.

Tracked adults from Lady Alice foraged in similar areas to previous years during incubation. Travelling around the west coast of the North Island and out to the Louisville Seamount Chain. Birds were undertaking reasonably long trips with an average of 13 days. No devices were retrieved from Ohinau Island, with adults being away for 12 days or more.

Fledging chicks tracked from Titi Island travelled north through the pacific, taking two routes either east or west up the North Island and then into the South Pacific Ocean, migrating past Vanuatu, New Caledonia and the Solomon Islands. This work reveals that there is a clear demarcation of migration routes between different populations of flesh-footed shearwater fledglings within New Zealand (at least within the first 30 days after fledging). In previous years, fledging chicks tracked from Ohinau Island maintained a migration route along the Kermadec/Tongan Trench.

WMIL recommendations include:

• Population monitoring on Ohinau and Lady Alice Islands be continued with 200 breeding study burrows monitored annually over two expeditions (Dec/Jan and Apr/May).
• The number of burrowscope burrows monitored annually continue to be 50 on each island.
• There is continued, focused effort to band and recapture as many flesh-footed shearwaters on the surface and in burrows on both islands.
• Titi Island, Marlborough Sounds, be considered as a potential future monitoring location.
• Repeat population estimates on Ohinau Island, Lady Alice Island and Titi Island be undertaken as soon as possible.
• Other breeding colony sites for flesh-footed shearwaters be considered for population estimates.
• Future tracking should use lighter devices with a maximum of 2.5% device body weight and be undertaken at Lady Alice, Ohinau and/or Titi Islands.
• Trial harnesses for chick tracking.
• A survival analysis be undertaken to estimate adult survival on each island.

Publication information

Ray, S. Burgin, D., Lamb, S., Olsthoorn, M. 2024. Toanui/flesh-footed shearwater population monitoring and estimates: 2023/24 season. Unpublished Wildlife Management International Technical Report to the Department of Conservation. 58 p.