Global assessment of marine plastic exposure risk for oceanic birds.

Plastic pollution is distributed patchily around the world's oceans. Likewise, marine organisms that are vulnerable to plastic ingestion or entanglement have uneven distributions. Understanding where wildlife encounters plastic is crucial for targeting research and mitigation. Oceanic seabirds, particularly petrels, frequently ingest plastic, are highly threatened, and cover vast distances during foraging and migration. However, the spatial overlap between petrels and plastics is poorly understood. Here we combine marine plastic density estimates with individual movement data for 7137 birds of 77 petrel species to estimate relative exposure risk. We identify high exposure risk areas in the Mediterranean and Black seas, and the northeast Pacific, northwest Pacific, South Atlantic and southwest Indian oceans. Plastic exposure risk varies greatly among species and populations, and between breeding and non-breeding seasons. Exposure risk is disproportionately high for Threatened species. Outside the Mediterranean and Black seas, exposure risk is highest in the high seas and Exclusive Economic Zones (EEZs) of the USA, Japan, and the UK. Birds generally had higher plastic exposure risk outside the EEZ of the country where they breed. We identify conservation and research priorities, and highlight that international collaboration is key to addressing the impacts of marine plastic on wide-ranging species.

Recovery of insular seabird populations years after rodent eradication.

Seabirds have been particularly affected by invasive non-native species, which has led to the implementation of numerous eradication campaigns for the conservation of these keystone and highly vulnerable species. Although the benefits of eradication of invasive non-native species for seabird conservation have been demonstrated, the recovery kinetics of different seabird populations on islands after eradication remains poorly evaluated. We conducted long-term monitoring of the number of breeding pairs of seven seabird species on a small atoll, Surprise Island, New Caledonia (southwestern tropical Pacific). Marine avifauna of the island were surveyed yearly 4 years before to 4 years after rodent eradication (conducted in 2005), and we conducted multiple one-time surveys from ∼10 years before and ∼15 years after eradication. We sought to determine how different seabird species responded to the eradication of invasive rodents in an insular environment. Three species responded positively (two- to 10-fold increase in population size) to eradication with differences in lag time and sensitivity. The number of breeding pairs increased (effect sizes = 0.49-0.95 and 0.35-0.52) for two species over 4 years post-eradication due to immigration. One species had a longer (at least 5 years) response time than all others; breeding pairs increased for over 10 years after eradication. Long-term sampling was necessary to observe the responses of the seabird populations on the island because of the delayed response of a species to eradication not visible in the first years after eradication. Our results confirmed the positive effects of eradication of invasive non-native species on seabirds and emphasize the importance of mid- and long-term pre- and posteradication surveys to decipher the mechanisms of seabird recovery and confirm the benefits of eradication for conservation purposes.

Las especies invasoras no nativas han afectados en lo particular a las aves marinas, lo que ha derivado en la implementación de numerosas campañas de eliminación para conservar estas especies importantes y muy vulnerables. Aunque se han demostrado los beneficios de la eliminación de especies invasoras no nativas para la conservación de las aves marinas, se conoce poco sobre la cinética de la recuperación de las diferentes poblaciones insulares después de la eliminación. Realizamos un monitoreo a largo plazo del número de parejas reproductoras de siete especies de aves marinas en Isla Surprise, Nueva Caledonia, un atolón pequeño en el suroeste del Pacífico tropical. Censamos anualmente la avifauna marina de la isla cuatro años antes y cuatro años después de la eliminación de roedores (realizada en 2005) y realizamos varios censos únicos de ∼10 años antes y ∼15 años después de la eliminación. Buscamos determinar cómo las diferentes especies de aves marinas respondían a la eliminación de los roedores invasores en un ambiente insular. Tres especies respondieron positivamente (un incremento poblacional de 2 a 10 veces mayor) a la eliminación con diferencias en el tiempo de desfase y en la sensibilidad. El número de parejas reproductoras incrementó (tamaños eficientes = 0.49 a 0.95 y 0.35 a 0.52) para dos especies cuatro años después de la eliminación debido a la inmigración. Una especie tuvo un tiempo de respuesta más largo (al menos cinco años) que las demás; las parejas reproductoras incrementaron más de diez años después de la eliminación. El muestreo a largo plazo fue necesario para observar las respuestas de las poblaciones de aves marinas en la isla porque una especie tuvo una respuesta retardada que no fue visible en los primeros años después de la eliminación. Nuestros resultados confirmaron los efectos positivos que tiene la eliminación de especies invasoras no nativas sobre las aves marinas y recalca la importancia de los censos a mediano y largo plazo antes y después de la eliminación para identificar los mecanismos de la recuperación poblacional y confirmar los beneficios con fines de conservación que tiene este método. Recuperación de las poblaciones de aves marinas insulares años después de la eliminación de roedores.

Nest-site selection and its influence on breeding success in a poorly-known and declining seabird: The Tahiti petrel Pseudobulweria rostrata.

The Tahiti petrel (Pseudobulweria rostrata) is a rare and declining seabird whose breeding biology and nest-site selection are poorly known. Nest-site selection is critical to seabird population fitness, and understanding the factors driving it is essential for designing effective conservation measures. Here, we measured several variables (topographical, physical and environmental) to characterize Tahiti petrel nesting habitats and burrows (i.e., width, height, depth and type: rocky cavity, dug into the soil or under a root) on Nemou Island in New Caledonia. The data were clustered using the HCPC (Hierarchical Clustering on Principal Component) method to identify principal habitat groups. This method was combined with logistic regressions to examine the influence of the variables on nest-site selection and breeding success. Our results showed that nest-site selection is linked to habitat groups (a combination of substrate and vegetation data), slope, orientation and soil depth, while breeding success is only influenced by nest characteristics (i.e., burrow type and width). Tahiti petrels prefer to nest on steep slopes in mature forests with rocky substrate and deep soil. Burrows were scatterred in small sub-colonies or isolated pairs, suggesting that nest-site selection depends on habitat quality rather than conspecific density. The study also revealed that breeding success is lower in rocky cavities and increases in burrows with wide entrances. Our nest-site selection survey is the first for the genus Pseudobulweria, and provides critical information for designing effective conservation programs in New Caledonia and the Pacific.

Behavioral and trophic segregations help the Tahiti petrel to cope with the abundance of wedge-tailed shearwater when foraging in oligotrophic tropical waters.

Two species breeding in sympatry are more likely to coexist if their ecological niches are segregated either in time, space or in trophic habits. Here, we combined GPS-tracking, stable isotope analysis and DNA metabarcoding analysis to understand how the rare Tahiti petrel Pseudobulweria rostrata (TP) copes with the very abundant (i.e. 500,000 breeding pairs) wedge-tailed shearwater Ardenna pacifica (WTS) when breeding in sympatry in a tropical area. WTS foraged in restricted areas along their path, while TP predominantly foraged using extensive search behavior, suggesting a more opportunistic foraging strategy. Interspecific overlap of foraging areas was higher than intraspecific overlap. Breeding seasons largely overlap between species during the study, but TP seems to be asynchronous breeders. TP fed upon prey with higher δ15N values than WTS, and their diet was mainly composed of deep-sea organisms. TP could feed upon dead prey floating at the surface while WTS preyed mainly upon fish species that generally move in schools. Our study highlights several segregating mechanisms (temporal, behavioral and trophic) that could facilitate the coexistence of the two species despite the predominant number of WTS, and provides the very first information on the foraging and trophic ecology of the poorly-known TP.

Plastic ingestion by seabirds in New Caledonia, South Pacific.

The accumulation of plastic pollutants in marine environments has many adverse effects on wildlife. In particular, marine predators are often exposed to accidental plastic ingestion, that may negatively affect survival due to the concentration of debris in the digestive tract. Among the species most vulnerable to plastic ingestion, seabirds are of major interest for conservation because of their wide foraging areas, long generation time and extended lifespan. We analysed stomach contents of 90 seabird specimens from 12 different species collected in New Caledonia to assess the local prevalence of plastic ingestion. Overall, we found plastic debris in 14.4% of sampled individuals, exclusively in procellariids: Gould's Petrel (41.2%, highest incidence), Tahiti Petrel (33.3%) and Wedge-tailed Shearwater (7.7%). To our knowledge, this study is the first characterization of plastic ingestion in seabirds from New Caledonia and our results show an overall lower ingestion prevalence compared to other assessments in the tropical Pacific.

Yelkouan shearwater Puffinus yelkouan presence and behaviour at colonies: not only a moonlight question.

We describe and test the influence of several environmental and biological factors on the presence and activity patterns of the Mediterranean endemic yelkouan shearwater Puffinus yelkouan at colonies. Bird arrival at breeding sites is highly correlated with nautical dusk for moonless or slightly moonlit nightfalls and correlated with moonset when the moon is visible. Breeding cycle and wind speed affect both the arrival times and presence at colonies. Bird activity also varies throughout the night and sex ratio on colonies throughout the breeding cycle in relation to breeding duties. Breeder and non-breeder behaviour particularly differs in the time spent on the ground outside burrows, without protection. Finally, factors other than moonlight can be essential in determining the presence and behaviour of petrels and shearwaters at breeding sites, and we need to determine how differences in behaviour at colonies could be related to differential predation risk.

Yelkouan shearwater nest-cavity selection and breeding success.

We describe, for the first time, nest-cavities selected by the Mediterranean endemic yelkouan shearwater Puffinus yelkouan on French islands, comparing it with the sympatric Cory's shearwater Calonectris diomedea. By monitoring 179 suitable cavities during four years, we show that yelkouan shearwaters select deeper cavities and with more winding tunnels than those selected by Cory's shearwaters or unoccupied cavities. Logistic regression modelling indicates that cavities with nest-like characteristics are not limited. We show that breeding success is enhanced in deeper cavities, with winding tunnels and higher block covers. We do not find any apparent competition between the two shearwater species.