Research Projects

Tetiaroa: consequences of an atoll restauration on seabirds, land crabs and ecosystem functioning.

Panorama paysage d'île

View of the hoa between Hiranae and Auroa, with Jayna during the monthly count of breeding seabirds.

Tetiaroa is an atoll 50 km North from Tahiti. Managing most of this atoll, the Tetiaroa Society is conducting an ambitious restauration program of the atoll, aiming at bringing it back to a state close to the pre-human period. A key step of this program is the removal of high impact invasive species, including the black and Polynesian rats, and yellow crazy ants. The removal of these species also offers unique opportunities to track how the ecosystem responds to this manipulation.

Rat Eradication Map

The Tetiaroa atoll includes twelve motu (= islets) with different histories of rat invasion / eradication. In 2022, rats will be eradicated from the entire atoll. Various species are affected by the presence of rats, including ghost crabs (Ocypode ceratophthalma, right), which are eaten by rats. Rats are also direct competitors of land crabs (Cardisoma carnifex, top left), engineers of the terrestrial ecosystems of these coral islands. The presence of rats is therefore likely to affect this species, with potential consequences on the functioning of ecosystems. In this project, we exploit this quasi-experimental context to understand how the abundance, morphology and behavior of crabs is altered in response to rat elimination, and what are the consequences of these changes on crab populations and on their ecosystems.

The functioning of ecosystems on intact atolls depends heavily on seabirds and crabs. Through their droppings, nesting seabirds bring nutrients (e.g., nitrogen) from the surrounding marine environment, enriching otherwise resource-limited ecosystems. Recent work has suggested that invasive rats could disrupt these nutrient inputs by reducing seabird populations, and thus decrease the productivity of surrounding terrestrial and marine environments. On the other hand, omnivorous land crabs dominate the resident terrestrial fauna, and they too play a key role in terrestrial atoll ecosystems. They are both predatory and scavengers, and influence seed dispersal, seedling recruitment and litter dynamics. They are thus referred to as “ecosystem engineers”.
Carlee setting up a trail camera to measure crab and rat activity.
Picture 2
Picture 2

Carlee setting up a trail camera to measure crab and rat activity.

By investigating spatio-temporal variation in seabird and land crab communities, this project aims at better understanding the functioning of atoll ecosystems in general, while measuring the impact of invasive species removal on these two faunal groups. The recent obtention of a research fellowship from the Fondation Fyssen will allow us to equip land crabs with pit tags to monitor their survival, and understand how behavioral changes may shape the response of crabs to rat removal.
Great crested terns
Brown boobies
Great crested terns
Brown boobies

10 seabird species nest in Tetiaroa, including Great crested terns (Thalasseus bergii, above) and Brown boobies (Sula leucoptera, below).

10 seabird species nest in Tetiaroa, including Great crested terns (Thalasseus bergii, left) and Brown boobies (Sula leucoptera, right).

This project is highly collaborative, as more than 12 (!) research teams from all over the World are investigating the impact of invasive species removal programs on Tetiaroa ecosystems (see the Tetiaroa Society’s website).

View of the hoa between Tiaraunu and Tauini

View of the hoa between Tiaraunu and Tauini

What about the yellow-crazy ant?

Yellow-crazy ants (Anoplolepis gracilipes) are present on several motus of Tetiaroa, and have reached very high densities on one of the most preserved ones, ‘A‘ie, where they already have obvious negative impacts on seabirds and invertebrate communities. Working with the Tetiaroa Society FP, we recently obtained the necessary funding from the OFB to eradicate this species from the atoll before it spreads more.

Listed as one of the 100 invasive species with the highest impact at the global level by the International Union for the Conservation of Nature (IUCN), the yellow crazy ant is now present on more than thirty islands in all four archipelagos of French Polynesia. To develop a better control of this invasive species in French Polynesia, we are researching the parameters explaining variation in yellow crazy ants density in Tetiaroa, while also investigating the ants’ impact on seabirds and land crabs. Miléna Philip joined the team in January 2022 to investigate these questions for her master project.
In collaboration with the Tetiaroa Society FP, we obtained a funding from the OFB (MobBiodiv Restauration) to attempt to eradicate the yellow-crazy ant from the atoll. Miléna was hired early August to organize this eradication. 

Ant map

Distribution of yellow crazy ants (Anoplolepis gracilipes) invasive in Tetiaroa. The photos on the left present the five species of ground-nesting seabirds in Tetiaroa, the most likely to be affected by ants (from top to bottom: brown noddy Anous stolidus, brown booby Sula leucogaster, crested terns Thalasseus bergii, gray-backed tern Onychoprion lunatus and sooty tern Onychoprion fuscatus). The three images at the bottom right show three of the land crab species in Tetiaroa that may be affected by ants (top to bottom: Ocypode ceratophthalmus, Cardisoma carnifex, Coenobyta perlatus). The photos at the top right illustrate the impacts of the yellow crazy ants on birds (brown noddy chick in ‘A’ie) and crabs (Christmas Island red crabs Gecarcoidea natalis).

Terrestrial bird communities of French Polynesia – interactions between introduced and native species

Birds of French Polynesia
Birds from all over the World have been introduced to Tahiti and other islands of French Polynesia. These exotic species are now the most commonly seen birds across the country.

The terrestrial bird communities of French Polynesia are largely dominated by introduced species, to the point where, especially in Tahiti, most native species are difficult to observe while introduced species are part of the Polynesians’ daily life, being particularly common in anthropized areas. How native and introduced species interact remains however poorly understood and a global assessment of terrestrial bird community structures across habitats is needed to investigate the impacts of introduced birds on native species. Using over 350 point-counts and 50 transects distributed in six high islands and one atoll of the Society archipelago, we have been characterizing the structure of terrestrial bird communities in diverse habitats, along gradients of urban development and at diverse altitudes. Thanks to a grant from the Fondation Fyssen, we developed this project in June-July 2022 by conducting 300 point counts in four islands of the Australes archipelago, while also displaying audio recorders in different habitats to precisely characterize the song phenology of both native and introduced species (see our interview on local television : Polynésie la Première, TNTV). We will also expand the project to the Marquesas starting in 2022.

The characterization of these terrestrial bird communities will serve as background data to investigate the impact of specific introduced species on native birds, and to monitor changes across time by regularly conducting these surveys.

Comparative analyses approaches – predicting the global impact of invasive species, favoring the success of reintroduction programs, understanding the impact of urbanization on native species

Some species appear to have a particular ability to establish successfully after a translocation event, and to adapt to their new environment. Similarly, the impact of urbanization varies substantially across species, and translocation success and adaptation to urban environments tend to be predicted by similar traits. The life history, genetic diversity, ecological niche width and behavioral plasticity of species are four components theoretically assumed to determine this establishment capacity and adaptation to urban environments, but their importance remains poorly understood. Using comparative analyzes, we aim at studying their relative importance in these different contexts (introduction success of exotic invasive species, translocation success for conservation purposes, and response to urbanization).

Using these same comparative analyses methods, we are also interested in responding to other global questions, including some with regards to bird diversification, the evolution of life history and behavior in vertebrates (and especially birds), and to the impact of variation in life history and behavioral strategies on species response to current global environmental changes.

Waders and waterbirds of French Polynesia: seasonality and habitat selection

Information on waterbirds in French Polynesia remains scarce and based on a few punctual studies. Thanks to regular transects and point counts, we aim at characterizing seasonal and spatial variation in the distribution of migratory waders, but also resident waterbirds.

Frigatebirds of the high islands of French Polynesia: seasonal variation in plumage and abundance

Frigatebirds mostly breed on uninhabited atolls in French Polynesia, including in Tetiaroa. To better understand their annual cycles, as well as the use of the high islands by the two species of frigatebirds occurring in French Polynesia, we systematically record any frigatebird observation in the high islands, identifying the species, age and sex of the individuals, and collecting information on plumage variation.

Lesser (Fregata ariel) and greater (F. minor) frigatebirds show substantial variation in plumage related to age and sex.