Rats are among the worst invasive alien predators. They prey upon eggs, chicks, and sometimes adults of seabirds, leading to the decline of many populations. Rats have invaded 93% of the islands in the western Indian Ocean, which is an avian biodiversity hotspot. Europa Island, Mozambique Channel, is a major seabird breeding site, where at least 1,000,000 pairs bred at the end of 20th century, including the endemic white-tailed tropicbirds (Phaethon lepturus europae). This species and the red-tailed tropicbird (Phaethon rubricauda) are vulnerable to predation by black rat (Rattus rattus), barn owl (Tyto alba), and pied-crow (Corvus albus) on Europa Island. In this study, we estimate the current population sizes of these tropicbird species and their breeding success. The impact of predators on tropicbird nests was quantified with camera traps. Finally, we model the dynamics of these populations under three management scenarios (no action, complete rat eradication, and targeted control of rats around nests). In 2019, 1,027 pairs of redtailed and 100 pairs of white-tailed tropicbirds bred on Europa Island, which indicates an annual decline of 5% and 17% since 2009, respectively. Breeding success of red-tailed tropicbirds and white-tailed tropicbirds was extremely low (0.08 ± 0.07 and 0.06 ± 0.03 respectively). Rats were detected at most surveyed nests and were the main predators of eggs and chicks. Pied-crows and barn owls also depredated nests occasionally. Population viability analysis projected a local extinction in 32-85 years for the red-tailed tropicbird, and in 11-50 years for white-tailed tropicbirds without conservation intervention. The complete eradication of rats would result in a rapid recovery of both populations. Rat control around nests only would result in population recovery only if 74% of the nests of white-tailed and 63% of the nests of red-tailed tropicbirds are free of rats.Une analyse des effets de la prédation des oiseaux de mer et de la viabilité de la population révèle un besoin urgent d'éradication des rats dans l'île Europa, dans l'ouest de l'océan Indien RÉSUMÉ. Les rats font partie des prédateurs étrangers les plus invasifs. Ils se nourrissent d'oeufs, d'oisillons et parfois d'oiseaux de mer adultes, ce qui provoque le déclin de nombreuses populations. Les rats ont envahi 93 % des îles de l'ouest de l'océan Indien, qui est un haut lieu de biodiversité aviaire. L'île Europa, dans le canal du Mozambique, est un site majeur de reproduction des oiseaux, puisqu'au moins un million de couples s'y reproduisaient à la fin du XXe siècle, notamment le phaéton à bec jaune (Phaethon lepturus europae). Cette espèce, ainsi que le phaéton à brins rouges (Phaethon rubricauda) est vulnérable à la prédation par le rat noir (Rattus rattus), la chouette effraie(Tyto alba) et le corbeau-pie (Corvus albus) sur l'île Europa. Dans cette étude, nous estimons la taille des populations de ces espèces d'oiseaux tropicaux et le succès de leur reproduction. L'impact des prédateurs sur les nids de phaétons a été quan...

BackgroundShearwaters (order Procellariiformes) are an excellent study system to investigate the genetic consequences of the co-called "seabird paradox", as they are able to disperse long distances but many species exhibit natal and breeding philopatry. However, few microsatellite markers are currently available for these taxa, hampering genetic inferences. Methods and resultsIn this study, 25 novel microsatellite loci were isolated and characterized for each of two distantly related shearwater species: the wedge-tailed shearwater (Ardenna pacifica) and the tropical shearwater (Puffinus bailloni). Polymorphism tests were performed for a total of 91 A. pacifica individuals sampled at Reunion and Round Island, and 48 P. bailloni individuals from Reunion and Europa Island, in the western Indian Ocean. The analyses revealed 23 polymorphic loci for A. pacifica, with the number of alleles per locus (Na) ranging from 2 to 8 (mean = 3.957 ± 0.364). Nineteen polymorphic loci were found for P. bailloni, with Na varying from two to five (mean = 3.053 ± 0.247). The observed heterozygosity (Ho) was relatively low for the two species, with Ho ranging from 0.022 to 0.725 (mean = 0.326 ± 0.044) for A. pacifica and from 0.021 to 0.688 (mean = 0.271 ± 0.051) for P. bailloni, but comparable to the estimates available for other Puffinus species.Please note that this is an author-produced PDF of an article accepted for publication following peer review. The definitive publisher-authenticated version is available on the publisher Web site. ConclusionsThe new microsatellite loci provide a valuable tool for further population genetic studies, and will allow for design of effective conservation and management plans for A. pacifica, P. bailloni and other closelyrelated species.