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Giant petrels Macronectes spp. are the largest avian predator-scavengers in the Southern Ocean and feed both by direct predation and by scavenging carrion. However, they are not considered to be predators of adult albatrosses. We report the first records of Southern Giant Petrels M. giganteus attacking and killing incubating Atlantic Yellow-nosed Albatrosses Thalassarche chlororhynchos on Gough Island. From 2017 to 2019, a total of 87 adult carcasses were found near nests within long-term monitoring areas. In 2019, 16 motion-activated cameras filmed 32 nests between September and January, during incubation up until chicks were no longer guarded by their parents. Camera footage revealed at least six different male Southern Giant Petrels independently attacking 11 incubating Atlantic Yellow-nosed Albatrosses, killing and feeding on 5 of those. We also recorded a Southern Giant Petrel attacking a brooding Atlantic Yellow-nosed Albatross and carrying its chick away. Of these camera-monitored nests breeding success was 18.75%, nest failure was due to parent mortality (n = 6), chick mortality (3) and nest abandonment (17), with giant petrels being confirmed or strongly suspected in at least 14 of 26 cases (54%). We observed these attacks in two out of 11 study areas, but it is uncertain whether this behaviour occurs elsewhere on Gough Island, or whether it is a novel hunting method learnt by a few individuals. However, if this behaviour spreads across albatross colonies, the resulting increase in adult mortality could have a significant impact on this endangered Atlantic Yellow-nosed Albatross population. [ABSTRACT FROM AUTHOR]

The impacts of invasive house mice Mus musculus have received increasing attention on islands where mice are the only invasive rodent species. On Gough Island, the impact of mice on seabirds has increased over the past decade, but the current population status of the Critically Endangered Gough Finch Rowettia goughensis is uncertain. Based on nest monitoring at high elevation sites in 2009 (n = 37) and 2018 (n = 45), we found mean nest survival of 55% in both years and a fecundity of 1.31 ± 0.69 fledglings per pair in 2018. Density estimates from territory mapping in 2009 and 2018 were similar to past estimates and indicated little change in upland habitat. Density estimates from line transect distance sampling surveys around the island from 2018 to 2020 revealed higher densities in moorland (55.4 birds/km2) and wet heath (29.5 birds/km2) habitats, compared to coastal tussock (10.9 birds/km2) and lowland fern bush habitat (2.6 birds/km2). Extrapolating these habitat-specific densities across the island indicates a global population of Gough Finches in 2020 of 1917 individuals (95% CI: 1550–2500). Future population surveys using the same design could detect population changes of 40% or more. Our population estimate provides an important baseline for future monitoring following the planned eradication of house mice from Gough Island in 2021. However, we highlight that greater monitoring effort may be needed to increase the power to detect smaller population changes after an invasive species eradication. [ABSTRACT FROM AUTHOR]

Invasive species are one of the greatest drivers of biodiversity loss worldwide, and the eradication of invasive species from islands is a highly efficient management strategy. Because eradication operations require large financial investments, uncertainty over the magnitude of impacts of both invasive species and their removal can impede the willingness of decision makers to invest in eradication. Such uncertainty is prevalent for long‐lived species that display an inherent lag between life stages affected by invasive species and those used for population status assessments.Albatrosses are amongst the longest‐living bird species and are threatened on land by invasive species and at sea by industrial fisheries. As in many seabird species, usually only a segment of the population (breeding adults) is used for status assessments, making it difficult to assess albatross population trends and the potential benefit of conservation action, such as the management of predatory invasive species.We used population monitoring and mark‐recapture data to estimate the past population trajectory of the critically endangered Tristan albatross Diomedea dabbenena by accounting for unobservable birds at sea in an integrated population model. We then projected the future population trajectory of Tristan albatrosses for scenarios with or without predation by invasive house mice Mus musculus on their main breeding site, Gough Island.The adult breeding population remained stable between 2004 and 2021, but breeding success was low (31%) and our model indicated that the total population (including unobservable immature birds) decreased from a median estimate of 9,795 to 7,752 birds. Eradicating invasive mice leading to a two‐fold increase in breeding success would result in a 1.8–7.6 times higher albatross population by 2050 (median estimate 10,352 individuals) than without this intervention.Low reproductive output for long‐lived species may lead to a cryptic population decrease, which can be obscured from readily available counts of breeding pairs by changes in the population structure. Mouse eradication is necessary to halt the ongoing population decrease of the Tristan albatross, even if this decrease is not yet apparent in the breeding population size. [ABSTRACT FROM AUTHOR]