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POP2022-01 Tākoketai/black petrel population monitoring - captures at sea 2024/25 (PDF, 4,155K)
Summary
Black petrel monitoring on Aotea /Great Barrier Island
This report is part of the ongoing study of the tākoketai/black petrel (Procellaria parkinsoni) on Aotea/Great Barrier Island that began in the 1995/96 breeding season.
During the 2024/25 breeding season, 486 tākoketai study burrows were intensively monitored within the Mt Hobson/Hirakimata study area on Aotea.
Throughout the study colony, there were 313 (64.4%) burrows occupied by breeding pairs, 106 (21.8%) occupied by non-breeding birds, and 67 (13.7%) were unoccupied at the time of check. Overall, 212 chicks were produced from the study burrows that are estimated to fledge representing a breeding
success rate of 67.7%. This does not include one chick that was banded in April 2025 but subsequently found dead outside the Department of Conservation Okiwi office, later on in June 2025, having presumably crash-landed on its maiden voyage.
Nine census grids were monitored within the study area and accounted for 200 of the inspected study burrows. Of these, 121 were occupied by breeding pairs (60.5%) and 78 chicks were produced representing a fledging success rate of 64.4%.
A total of 714 adults and 218 fledgling chicks were captured during the 2024/25 field season of which with 143 adults were banded this season. Of the 218 fledgling chicks banded during the 2024/25 field season, 213 were banded in study burrows and five chicks were banded in unmarked burrows.
There have been nocturnal surveys undertaken throughout the 30-year study period, but only over the past four seasons (2021/22 to 2024/25) has this effort been increased to 6-8 hour (between 9.15 pm to 5.15 am) searches each night. Over 940 nights of ad-hoc surveys undertaken between 1995/96 and
2020/21, 811 adults were recaptured, of which 365 were already banded and 108 were returned chicks.
Over 51 nights of intensive surveys between 2021/22 and 2024/25, 516 adults were recaptured, of which 285 were already banded and 106 were returned chicks. At-sea surveys have also been conducted by WMIL over this same period with only 22 banded birds being caught and nine being recaptured chicks
(Burgin 2024). The percentage of banded tākoketai caught out of all captures is higher for intensive night surveys (51.3%) than the ad-hoc surveys (45%). This pattern is also the same for the percentage of returned chicks captured (intensive 19.4%, ad-hoc 13.3%), for the number of banded tākoketai caught per survey (intensive n=5.3, ad-hoc n=2.1) and for returned chicks caught per survey (intensive 2.0 returned chicks/survey, ad-hoc 0.6 returned chicks/survey).
There have been a total of 491 returned chicks recaptured at the colony since they were banded prior to fledging. Of these, 138 returned chicks were identified during the 2024/25 breeding season; 34 of which were caught for the first time at the colony. Not all cohorts were represented this season as no
re-captures of returned chicks were made from the 1995/96, 2000/01 and 2002/03 cohorts. Nonetheless, this season saw the highest number of cohorts represented (by at least one individual).
Over the entire study, the majority of the 491 returned chicks were from the 2010 /11 cohort followed by the 2006/07 cohort. Understanding the factors affecting return rates of chicks within the 35-ha study site is vital. It is important to determine whether it is related to low juvenile survival and/or recruitment or if it is simply due to a lack of detection. Understanding juvenile survival and recruitment is necessary for accurate demographic modelling and for species risk assessment modelling. Therefore, it is recommended that efforts to obtain this data is completed with urgency.
There was a single feral cat predation event on an unbanded adult tākoketai (not an individual from the study burrows but found in the wider study area) and two rat predation events at the study colony on Hirakimata this season. Introduced species still pose a threat to the tākoketai population and it is
imperative pest control measures continue.
At sea captures
This at-sea capture project continues work started in 2022 to look at survival and return rates of juvenile black petrels not visiting the main study areas on Aotea/Great Barrier Island. Capture-mark-recapture of black petrels in the Hauraki Gulf will also provide information from a random sample of birds away from the study colonies to help estimate current population size of this species.
The main objective for the 2024-25 season was to capture black petrels at-sea to determine the proportions of unbanded birds versus banded birds. This information will be used to assess if apparent low juvenile survival is biased by dispersal away from study colonies. Information collected from marked versus unmarked birds in this study will be analysed in a separate project to estimate the overall population size of black petrels.
Fieldwork was conducted across four trips between January and April 2025, targeting more offshore areas to broaden the search range for birds. Using a refined net gun technique that was developed for live capture of seabirds at sea, 351 black petrels were captured and processed, with 25 recaptures recorded. The average processing time and capture rates both increased compared to the previous season.
The data from this report and previous seasons will be used in the analysis of black petrel demographic rates, for a better understanding of their overall numbers and population structure as part of a separate CSP contract.
Publication information
Bell, E.A.; Lamb, S. & Ray, S. (2025). Key demographic parameters and population trends of tākoketai/black petrels (Procellaria parkinsoni) on Aotea/Great Barrier Island: 2024/25. Unpublished Wildlife Management International Ltd. Technical Report to the Conservation Services Programme, Department of Conservation, Wellington.
Gaskin, C., Whitehead, E. 2025. Black petrel population monitoring: captures at sea. POP2022-01 final report provided by Northern New Zealand Seabird Trust to the Conservation Services Programme, Department of Conservation, Wellington. 33 p.