T.A.R.P. | Rat eradication

This operation is part of the Tetiaroa Atoll Restoration Program (TARP), which aims to protect seabirds, crabs, and native vegetation by eradicating invasive rats. The primary goal of this mission was to treat the motus Tauvini and Ahuroa, located near Ti'ara'aunu, as a preventive measure, and to target Ti'ara'aunu, the motu where rats are still present. Another objective was to prepare for the installation of monitoring cameras to assess the success of the treatment and plan the next steps for ecological surveillance.

Collaborators: Lusiano and Tuterai (rangers), Tehiana and Hina (nature guides), Joan (Scientific Activities Coordinator), Della, Teora, Carlos, Maria, Mattia, Eugenia, Pasquelin, Cédric, Muriel, Carole, Haiata, Teva, Karine, Stéphane (volunteers)
Date of stay: September 1 to 5 and September 22 to 29

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Summary of field activities

The first mission took place from September 1st to 5th, 2025. During this period, Tauvini and Ahuroa were fully treated as a precaution, due to their proximity to Ti'ara'aunu, which increases the risk of reinfestation. A first section of Ti'ara'aunu was also covered. However, progress was significantly slowed by dense vegetation and difficult terrain. Walking through thick bush while carrying 10–12 kg buckets was a real physical challenge for participants. This first phase involved 15 people, including 12 volunteers and 3 Tetiaroa Society staff. Each pair walked about 3 km of bait lines per day, placing bait every 20 meters according to protocol.

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The second mission ran from September 22nd to 29th, 2025, and completed the treatment of Ti'ara'aunu. 13 people took part, including 10 volunteers and 3 staff members. Over 10 days, 167 bait lines were treated, covering all 165 hectaresof Ti'ara'aunu — the largest and one of the most challenging motus on the atoll. The bait lines had been previously cleared and marked every 20 meters. Bait was weighed and packed into 10–12 kg buckets. Most buckets were dropped at the start of each line, making initial access easier, but often forcing teams to carry multiple heavy buckets over long distances — sometimes up to four per line. Ideally, buckets would also have been dropped further inland to reduce transport time and effort. However, due to a limited number of available buckets, teams had to refill and redeploy them throughout the operation, which reduced efficiency. If enough buckets had been available from the beginning, all could have been pre-positioned, significantly lightening the workload. Each pair distributed 1 kg of bait per marked point, covering around four lines per day on average.

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Impacts and preliminary results

The operations on Tauvini and Ahuroa were completed successfully. Monitoring cameras were installed post-treatment, and no rat activity has been detected on either motu. On Ti'ara'aunu, the treatment covered the entire motu. Monitoring cameras have not yet been installed, but their deployment is highly recommended to confirm rat eradication and assess whether another treatment will be needed during the next dry season. The entire operation was carried out without major incidents, thanks to strong coordination between volunteers and the Tetiaroa Society team. 

Perspectives

The next critical step will be the installation of monitoring cameras on Ti'ara'aunu to closely track the post-treatment situation. This step is essential to confirm the complete disappearance of rats and determine the need for further intervention. Scientists are also planning to select a pilot site for the new ATTRACT program, aimed at promoting the recolonization and long-term monitoring of seabird species on rat-free islands. Before this phase begins, it is crucial to ensure that all invasive species, especially rats, have been fully eradicated. A field survey will need to be conducted in the coming months to verify the treatment's success and assess the current ecological status of Ti'ara'aunu. While no timeline has been set yet, this check will be a key milestone before launching the ATTRACT project on the atoll.

In May 2025, a quarterly seabird survey was conducted over approximately 35 km of transects covering the atoll's 11 motu (excluding the hotel area). Observations included counting nests, eggs, chicks, juveniles, and adults, as well as the types of trees used for nesting. Checks were also carried out on the rings present on certain individuals, particularly brown boobies, and the data were transmitted to the University of Washington. 

A set of camera traps was maintained to monitor the breeding of white terns, brown noddies, great crested terns, grey-backed terns, frigate birds, and masked boobies. An additional camera was installed on a new masked booby nest, allowing for a fourth successful hatching since rat eradication. Brown boobies were captured in partnership with an international research team to be ringed, measured, and fitted with tracking tags. 

Feathers and eggshells were collected from dead and newly hatched birds. These samples were sent for isotopic analysis (nitrogen, carbon) and to measure mercury levels, as part of a study on the contamination of marine predators worldwide. 

Monitoring of land crabs was carried out along the transects, with a daytime count of visible individuals and observations of their feeding or reproductive behavior. 

Finally, a study of tahinu (Heliotropium arboreum) was continued at 20 sites across the atoll. Measurements included leaf growth, leaf replacement, herbivory rates, and herbivorous insect density. These surveys were conducted by a master's student from the Bordeaux School of Agronomy.

Preliminary results
Several notable observations were made during this mission:

• A fourth masked booby birth has been confirmed, again at the same nesting site.
• Ghost crabs have been heard calling in their burrows, a rare behavior that has been little studied, and the conditions of its occurrence (moon, time, season, etc.) are currently being thoroughly documented.
• An unprecedented nesting phenomenon of grey-backed terns has been observed, with several dozen pairs settling in at the same time. Unfortunately, these colonies have settled in an area exposed to swell and disturbances caused by visitors.
• A strong presence of birds was observed, much greater than in the previous two years. After the disruptions linked to an epidemic (2023) and El Niño (2024), this season could represent a return to favorable conditions.

The terns are thriving on Tetiaroa

The new images from the camera traps should provide a better understanding of the breeding behavior of crested terns and grey-backed terns, two species that are still poorly documented on the atoll.

Monitoring of bird and crab populations will continue quarterly, with missions planned for August and November 2025. Monitoring of the breeding success of seabirds will be maintained using camera traps.

In July 2025, capture-mark-recapture sessions will be conducted on ghost crabs to study the evolution of their populations and their morphological characteristics since the eradication of rats. Similar operations are planned for hermit crabs to estimate their densities and observe the exchange of shells between individuals depending on the site. A detailed characterization of the habitat will also be carried out on the 350 transects used for bird monitoring over the past four years. This step will provide a better understanding of the species' preferences for nesting trees.