Latest report on a long-term study: the Black Petrels of Great Barrier Island

Black Petrel chick by Maureen Bennetts of Artists & Biologists Unite for Nature (ABUN), after a photograph by Biz Bell

Elizabeth ‘Biz’ Bell (Wildlife Management International, New Zealand) and colleagues have produced a final report for the Conservation Services Programme of the New Zealand Department of Conservation that summarizes research conducted on ACAP-listed Black Petrels Procellaria parkinsoni on Aotea/Great Barrier Island.

The report’s Executive Summary follows:

“This report is part of the ongoing study of the tākoketai/black petrel (i) 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%)  ccupied by non-breeding birds, and 67 (13.7%) were unoccupied at the time of check. Overall, 212ochicks 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.

WMIL recommends that:

• Intensive population monitoring using the study burrows on Aotea continues with three visits (i.e., at egg-laying (December); at chick hatching/chick guard in late January/early February and at chick fledging in late April/early May) per season to the colony to track population trends and determine impacts to the birds and colony.
• Multiple-night expeditions to focus on recruitment (i.e., nocturnal surveys to capture pre-breeders and returned chicks) to the Aotea study colony continue to determine juvenile survival and recapture probabilities.
• Implement a remote/trail camera monitoring network at key-launch sites around the colony to identify potential time-windows of peak population activity outside the routinely monitored timeframes
• Sexing of all tākoketai caught during the recruitment expedition and in the study, burrows is completed to determine any sex biases and survival differences between sexes at the colony and within the study burrows.
• A focused, consistent and repeatable mark/recapture session (e.g., a 2-hour capture period at known launch sites) is completed over a number of nights to capture as many banded and unbanded birds as possible. Data can then be used to provide another population estimate and compared to estimates obtained from at-sea captures and burrow monitoring.
• Transect surveys across the core tākoketai habitat (1000 ha around the summit) are undertaken to provide an updated population estimate for the core breeding area of Aotea.
• Syatellite tracking of chicks to, and in, South American waters is undertaken to determine migration routes and foraging areas to estimate risk in these areas.
• The possibility of collaborative at-sea capture expeditions in Ecuador is investigated. Discussions between DOC and New Zealand Government with Ecuadorian Government and researchers will have to be conducted to enable this type of collaborative work. At-sea work in Ecuador could determine the level of juvenile tākoketai presence in this area and risk within this area, and this mark/recapture work could provide another population estimate to compare with the New Zealand data.
• Further investigation to determine whether particular areas of the colony are more at risk to rainfall events than others (e.g., burrows in flatter areas being more prone to flooding) as a preliminary assessment on climate resilience.
• In-depth modelling on the effect of age, age difference in pairs, and experience on breeding success is completed to understand this relationship in tākoketai.
• Analysis of, and comparison between, breeding success in public, and non-public, access areas is completed to determine whether human disturbance is a factor at the Aotea colony.
• Investigation into possible deterrence methods of all predators, but specifically feral pigs and feral cats, should be continued at Cooper’s Castle.

Reference:

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.  Wildlife Management International Ltd. Technical Report to the Conservation Services Programme.  Wellington: Department of Conservation.  40 pp.

John Cooper, Emeritus Information Officer, Agreement on the Conservation of Albatrosses and Petrels, 28 August 2025