Méringo H De

J.-C Gaertner

Feral cats threaten the biodiversity of French Polynesia: some island-dependent patterns

BACKGROUND AIMS

METHODS

RESULTS

DISCUSSION

CONSERVATION IMPLICATIONS

Invasive populations of feral cats Felis catus strongly threaten the native fauna on islands worldwide (Doherty et al. 2016, Palmas et al. 2017). French Polynesia, located in the South Pacific and formed by 120 tropical and subtropical islands divided in five archipelagoes, harbors several threatened endemic bird species.

Feral cats which were introduced by Europeans less than 200 years ago, are currently present in most habitats of many atolls and high volcanic islands, but their abundance and impacts remain largely understudied compared to other invasive mammalian predators such as rats.

The French Polynesian islands can be considered as multi-invaded systems with different assemblages of introduced rodents. The impact of feral cat populations is assumed to be higher in presence of introduced rodents and may also vary according to the rodent species. In particular, black rats Rattus rattus, which constitute a constant and abundant resource, can help sustain feral cat abundance at a high level, thereby exacerbating predation pressure on native wildlife via the "hyperpredation" process (Courchamp et al. 1999, Ringler et al. 2015).

We investigated the impacts of feral cats on biodiversity in four contrasted inhabited high volcanic islands in French Polynesia, particularly in terms of alien rat species, by studying:

-feral cat trophic ecology and predated endemic bird species; -abundance of feral cat populations. • We showed unreported patterns of feral cats predation in islands.

STUDY SITES

• At least 2 endemic bird species (fruit doves, Columbidae) were predated.

• Surprising relative abundances with more feral cats on islands harboring 1 or 2 species of rodent (Ua Huka with only Rattus exulans ; Tahuata with R. exulans and R. rattus).

Pati'oti'o

Pomarea iphis Iphis monarch

Ua Huka endemic

Funded by : Government of French Polynesia Délégation à la Recherche J-.Y. Meyer

Marquesas Islands:

Ua Huka , 83 km² (with R. exulans) Tahuata , 69 km²(with R. rattus, R. exulans)

Society Islands:

Moorea , 135 km² (R. rattus, R. exulans, R norvegicus) Tahiti , 1045 km² (R. rattus, R. exulans, R norvegicus) ? ?

Occurrence frequency of 4 prey categories

Our study reveals feral cat presence and both day and night activity à Although free of black rats Rattus rattus, the island of Ua Huka urgently needs a more in-depth study in order to elaborate an efficient management plan against feral cats. à Bird conservation in the different islands of French Polynesia requires specific studies on invasive predators before implementation of management actions.

• The GI index could provide an alternative management tool for monitoring feral cats relative abundance between sites or changes in populations with time.

Fo

  per island and 2 periods of survey (2018 and 2019) • 20 baited camera traps • 15 days of monitoring • 2 cam-traps per theorical home range • both day and night • General Index (GI) of feral cat activity by measuring the mean of camera capture events (i.e. cat photos) per sampling effort Camera trap deployment design in Vaitahu valley, Tahuata island (Marquesas)Nota-Bene: this work is still ongoing and the analysis of data from the 2019 sampling period will confirm and clarify these patterns and conclusions (particularly concerning the bird species affected by feral cat predation)

  bird species (IUCN Red List status according toMNHN et al. 2015)