Black petrel monitoring on Aotea/Great Barrier Island 2023/2024
Introduction
This is the final report for POP2022-01 Black petrel research. Published September 2024.Download the publication
Summary
This report is part of the ongoing study of the tākoketai/black petrel (Procellaria parkinsoni) on Aotea /Great Barrier Island that began in the 1995/1996 breeding season.
During the 2023/24 breeding season 482 tākoketai study burrows were intensively monitored within the Mt Hobson/Hirakimata study area on Aotea.
There were 306 (63.5%) burrows occupied by breeding pairs, 58 (12%) occupied by non-breeding birds, and 118 (24.5%) were unoccupied at the time of check. Overall, 222 chicks were produced from the study burrows representing a fledgling success rate of 72.5%, but five chicks were found to be below weight and smaller in size during the May chick banding trip, and most of these chicks were not expected to survive to fledging. This would further reduce overall breeding success to 70.9%.
Nine census grids were monitored within the study area and accounted for 199 of the inspected study burrows. Of these, 120 were occupied by breeding pairs (60.3%) and 86 chicks were produced representing a fledging success rate of 71.7%. Again three of these chicks were in poor condition and were not expected to fledge, reducing breeding success to 69.2%.
A total of 700 adults and 223 fledgling chicks were captured during the 2023/24 field season with 274 adults banded this season (including 204 from study burrows). Of the 223 fledgling chicks banded during the 2023/24 field season, 212 were banded in study burrows and eleven chicks were banded on the surface or from random non-study burrows. An additional ten chicks from within the study burrows fledged prior to the banding trip in May.
There have been nocturnal surveys undertaken throughout the 29-year study period, but only over the past three seasons (2021/22 to 2023/24) 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 41 nights of intensive surveys between 2021/22 and 2023/24, 427 adults were recaptured, of which 219 were already banded and 83 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%) and much higher than the at-sea surveys (4.8%). This pattern is also the same for the percentage of returned chicks captured (intensive 19.4%, ad-hoc 13.3% vs at-sea 2%), for the number of banded tākoketai caught per survey (intensive n=5.3, ad-hoc n=2.1, at-sea n=1.5) and for returned chicks caught per survey (intensive 2.0 returned chicks/survey, ad-hoc 0.6 returned chicks/survey, at-sea 0.6 returned chicks/survey).
There have been a total of 461 returned chicks recaptured at the colony since they were banded prior to fledging. Of these, 126 returned chicks were identified during the 2023/24 breeding season; 30 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, 1996/97, 2001/01 and 2003/04 cohorts. Over the entire study, the majority of the 461 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 effort to obtain this data is completed with urgency.
Additional monitoring of feral pig and other predator occurrence and impact on tākoketai at Cooper’s Castle was undertaken this season. Visual deterrents were established at two breeding burrows with trail cameras placed to record images and video. Footage confirmed rat presence only. There were no feral cat predation events 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.
- 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.
- Satellite 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.
Publication information
Bell, E.A.; Lamb, S. & Ray, S. (2024). Key demographic parameters and population trends of tākoketai/black petrels (Procellaria parkinsoni) on Aotea/Great Barrier Island: 2023/24. Unpublished Wildlife Management International Ltd. Technical Report to the Conservation Services Programme, Department of Conservation, Wellington. 67 p.