atoll fern

T.A.R.P. | Rat eradication

Island restoration
  1. Tetiaroa Society Programs
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  3. T.A.R.P. | Rat eradication

T.A.R.P. | Rat eradication

Introduced rats are a major problem on Pacific islands. The rats thrive on coconuts but also eat seabird and turtle eggs and hatchlings, as well as invertebrates, and plants. Tetiaroa Society is working with invasive species specialists from around the world to rid the island of this serious pest.

Principal Investigators: Baudouin des Monstiers, Richard Griffiths, Frank Murphy
Affiliations: Island Conservation, Tetiaroa Society
Project Dates: 2018 - ongoing

Update : Effects of rat eradication on terrestrial ecosystems of Tetiaroa

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.

Update : 2024

There is ongoing monitoring to make sure that rats do not move to other nearby motu. The good news is that the Polynesian rat is much less mobile and less disruptive to the ecosystem than the Ship Rat. The rest of the island has been completely rat free now for over a year and the response of bird and crab populations has been spectacular as you will see in some of the project reports here.

Image
working to eradicat invasive rats
map of rat-free areas of Tetiaroa atoll

Update : 2023

In 2018 Tetiaroa Society and Island Conservation carried out a successful rat eradication on Motu Reiono. Then in 2020 another eradication was done on Motu Onetahi and Honuea. In 2022 an attempt was made at eradication across all the remaining motu. Unfortunately, in follow up field work rats were detected in small numbers on some of the motu. A decision was made at that point to create a team that would work to detect rats and then eliminate them motu by motu. 

This work spanned all of 2023 and, although it has gone slowly, there has been a marked reduction in numbers and some of the remaining motu are now rat free. We will continue this work into 2024, when we expect to make the whole of Tetiaroa totally rat free. Note that after the large operation in mid-2022 the numbers of rats have been so small that the island ecosystem has essentially been rat free. You will hear about the effect of this in other TARP projects. 

team on the motu
off to work
and another motu

Update: March 2020

Restoring tropical islands provides an unrivaled conservation opportunity. Island restoration programs protect our world’s rare and endangered species, and might also boost the resilience of their surrounding coral reefs to the effects of climate change.

As part of its Tetiaroa Atoll Restoration Program (TARP), Tetiaroa Society is carrying out a major conservation intervention on Tetiaroa (French Polynesia) in 2021. The program aims to restore seabird populations and to establish Tetiaroa as a sanctuary for seabirds, green sea turtles, coconut crabs, and translocated endangered endemic birds. In addition, we propose to leverage the unique capacity of the site and our partners to scientifically establish the value of atoll restoration for coral reef conservation. The conservation science we propose will extend studies that suggest seabird colonies might increase the resilience of coral reefs through the fertilizing effect of nutrients from the bird’s guano. Testing this hypothesis on Tetiaroa, and demonstrating the underlying ecological mechanisms, will complement traditional Polynesian knowledge and help raise awareness of the importance of restoring natural land-sea connections for biodiversity conservation and sustainable human development.

Starting in March 2020, the current project will engage world-class experts in cutting-edge restoration, biosecurity, and scientific research. It will provide excellent training opportunities for Tetiaroa Society’s team of local rangers and naturalist guides. Such training is crucial for implementing biosecurity protocols to establish Tetiaroa as a wildlife sanctuary, allowing initiation of translocation programs for endangered birds. Communicating the science underlying the restoration efforts will build capacity among local conservation managers and benefit local schools through Tetiaroa Society’s Education Program, which is carried out in partnership with Polynesian cultural associations.

sprout URL

The comprehensive scientific surveys from nutrients and microbes to marine and terrestrial landscapes, carried out before and after the recovery of seabird populations, will provide crucial evidence for how atoll restoration improves the resilience of coral reefs encouraging similar efforts to restore health land-sea nutrient flows elsewhere.

  • Planning on Onetahi Planning on Onetahi
  • Team members ready to go Team members ready to go
  • Rattus exulans on motu Reiono Rattus exulans on motu Reiono
  • Yes, we have all of our equipment Yes, we have all of our equipment
  • Predator caught on camera Predator caught on camera
  • Atoll restoration team member on Tetiaroa Atoll restoration team member on Tetiaroa
  • A rat in action on the atoll A rat in action on the atoll
  • Team member throwing bait Team member throwing bait
  • Goodbye to Onetahi's rats Goodbye to Onetahi's rats
effects of rat eradication

The Tetiaroa Society Conservation and Sustainable Use Plan (CASUP) envisages an atoll where the terrestrial and marine habitat has been restored to as close to its original native form as possible. It is imperative that we do our utmost to allow this and other islands to be as resilient as possible to the future effects of climate change. To that end, the Tetiaroa Atoll Restoration Project (TARP) focuses on the removal of invasive species and restoration of native species.

Rat Eradication and its Consequences

The TARP is beginning with the most significant invasive species on the atoll: the ship rat and the Polynesian rat. These rats severely reduced the native bird population of Tetiaroa, and also feed on green sea turtle hatchlings, plants, crabs and other invertebrate species. With both species of rat successfully removed, Tetiaroa would become a major sanctuary for not just birds but also other native fauna and flora. This would open the potential for transplanting very rare and threatened species from the small remaining populations elsewhere in French Polynesia to Tetiaroa.

Remarkably though, the effects of rat removal don’t stop at the shoreline. The enhancement of the seabird population brings much needed nutrients to the island and the effects from this will cascade down through plant, invertebrate, soil, and marine community ecology. Studies in the Chagos Archipelago have shown that natural seabird populations contribute to the health of the adjacent coral reef. On Tetiaroa the TARP has a chance to record this in real time and develop a model for the sustainable management of tropical islands and their coral reefs in these uncertain times.

Project Plan

Rat eradication is set for August and September of 2020. In order to understand the effects of the removal of a high level predator like rats, baseline data will be collected in all habitats on the island before this date. Surveys will be conducted of seabirds, plants, terrestrial invertebrates, fish, and algae. Transects will be set up to monitor coral and algae cover across the barrier reef system. Water chemistry and microbiome data will be collected from the ground water of the motu to the outer reef. There will also be experiments set up in order to better understand rat eradication in the tropics and that will give researchers insight into how eradication differs if there is more than one species present. This pre-eradication work will be extremely important in order to allow for detailed follow up work for years to come.

Invasive Invertebrates

In parallel to the main focus on rats, other invasive species would also be targeted for eradication. These include: (i) two species of mosquitoes (a significant nuisance for humans and potential disease vector for all terrestrial vertebrates on Tetiaroa), (ii) one species of biting flies (nonos), (iii) two species of invasive ants (which are major ecosystem engineers like rats).

A research and control program carried out by Institute Louis Malarde and sponsored by The Brando and Tetiaroa Society has successfully controlled one species of mosquito on Motu Onetahi, and is working on other species and control of biting flies on Motu Rimatuu.

Invasive Plants

The third major component of the TARP would be to follow recommendation from the Flora and Vegetation chapter of the CASUP and work on removing some percentage of the coconut palms that are in unnaturally dense stands due to the farming of coconuts from the 1930s to 1966. This would allow for other native trees and plants to repopulate the motu. Experiments on the removal of coconut palms need to be carried out and monitored to see how best to restore native motu forest.

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