Prions Pachyptila are the most abundant seabirds in the Southern Ocean and comprise two main groups: those with and without bill lamellae to filter zooplankton. With few exceptions, each breeding location supports at most one species from each of these groups. However, Gough Island supports two morphologically very similar, filter-feeding species: broad-billed P. vittata and MacGillivray's prions P. macgillivrayi. To understand how these two species co-occur in sympatry, we compared the foraging ranges, habitat selectivity, trophic segregation and moult schedules of these species using combined geolocation-immersion loggers. After breeding, both species showed a well-defined westward migration prior to moulting. Moult lasted 11 to 19 weeks and was significantly longer in MacGillivray's than broad-billed prions. Moulting birds occurred in specific areas within the Argentine Basin, with little overlap between the two species. Habitat analysis revealed species-specific preferences, in particular sea surface temperature. Activity patterns also differed; MacGillivray's prions spent more time in flight, which indicates a more active foraging strategy, relying less on filter feeding. Stable isotope ratios (δ 15 N) in flight feathers were greater in MacGillivray's prion, which is consistent with its less specialized bill morphology resulting in feeding at a higher trophic level. Inter-specific spatial segregation was observed for most of the tracking period, in large part because broad-billed prions breed roughly 3 months earlier than MacGillivray's prions. At Tristan da Cunha, 250 km farther north, where only broad-billed prions breed, they departed, moulted and returned significantly later (15-17 days) than conspecifics from Gough Island, providing evidence for character displacement in sympatry with MacGillivray's prion.

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The use of miniaturized video cameras to study the at-sea behavior of flying seabirds has increased in recent years. These cameras allow researchers to record several behaviors that were not previously possible to observe. However, video recorders produce large amounts of data and videos can often be timeconsuming to analyze. We present a new technique using open-source software to extract bank angles from bird-borne video footage. Bank angle is a key facet of dynamic soaring, which allows albatrosses and petrels to efficiently search vast areas of ocean for food. Miniaturized video cameras were deployed on 28 Wandering Albatrosses (Diomedea exulans) on Marion Island (one of the two Prince Edward Islands) from 2016 to 2018. The OpenCV library for the Python programming language was used to extract the angle of the horizon relative to the bird's body (= bank angle) from footage when the birds were flying using a series of steps focused on edge detection. The extracted angles were not significantly different from angles measured manually by three independent observers, thus being a valid method to measure bank angles. Image quality, high wind speeds, and sunlight all influenced the accuracy of angle estimates, but post-processing eliminated most of these errors. Birds flew most often with cross-winds (58%) and tailwinds (39%), resulting in skewed distributions of bank angles when birds turned into the wind more often. Higher wind speeds resulted in extreme bank angles (maximum observed was 94°). We present a novel method for measuring postural data from seabirds that can be used to describe the fine-scale movements of the dynamic-soaring cycle. Birds appeared to alter their bank angle in response to varying wind conditions to counter wind drift associated with the prevailing westerly winds in the Southern Ocean. These data, in combination with fine-scale positional data, may lead to new insights into dynamic-soaring flight. del viento para contrarrestar la deriva del viento asociada con los vientos predominantes del oeste en el Oc eano Austral. Estos datos, en combinaci on con datos posicionales a escala fina, pueden conducir a nuevas ideas sobre el vuelo de planeo din amico.

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.

The Blue Petrel Halobaena caerulea breeds at five subantarctic island groups and at islands off southern Chile in a narrow latitudinal band from 47° to 56° S on either side of the Antarctic Polar Front. We found a colony on Gough Island (40° S, 10° W), central South Atlantic Ocean, more than 700 km north of its known breeding range. Breeding appears to take place later than at colonies farther south. Although the colony is in a fairly frequently visited part of the island, it might have been overlooked rather than representing a recent range extension.