Understanding the mechanisms underlying the emergence and spread of high pathogenicity avian influenza virus (HPAIV) is critical for tracking its global dissemination, particularly via migratory seabirds, given their role in transmission over long distances. Scavenging seabirds, such as skuas, may act as both reservoirs and vectors, and have been linked to multiple outbreaks since 2021. Here, we report the detection of HPAIV H5N1 clade 2.3.4.4b in three Tristan skua (Stercorarius antarcticus hamiltoni) carcasses on Gough Island in the central South Atlantic Ocean. To investigate potential incursion routes, we combined genomic analyses with year-round tracking data from global location sensors. Although migratory movement patterns suggested southern Africa as the most obvious pathway, the strain detected on Gough Island was more closely related to that identified in South Georgia, indicating that infection may have occurred during the pre-laying exodus, when skuas disperse into frontal waters south of the island. No further cases have been confirmed for Gough, but more systematic monitoring is needed to understand the dynamics of virus infection. The detection of HPAIV H5N1 in skuas on Gough Island highlights the importance of continued vigilance, proactive and geographically inclusive surveillance strategies, and biosecurity measures globally, alongside efforts to reduce other pressures on globally important seabird populations to help strengthen their resilience.

Predator-prey relationships on islands are often profoundly altered by invasive species. Brown skuas Catharacta antarctica are predator-scavengers at sub-Antarctic islands, where their population dynamics are linked to food availability. On Marion Island, skua population size and breeding distribution appear to have shifted in response to changes in burrowing petrel populations, which were severely impacted by feral cat Felis catus predation before cats were eradicated in 1991. We compare estimates of brown skua population size, breeding distribution, and fledgling production on Marion Island from studies conducted between 2010 and 2023 to earlier studies before cats were eradicated, including an extensive survey in 1987–1988. With increased search effort in 2023, we recorded 983 breeding territories, exceeding the 1987–1988 estimate of 878 territories, despite a slight decrease in average production, from 1.26 fledglings per pair per year in 1987–1988 to 1.10 between 2010 and 2022 (n = 3 surveys). Most notably, there has been a shift in the distribution of breeding sites: territories in coastal areas where skuas mainly prey on penguins have increased by 39

Seabirds are excellent ecosystem indicators and are amongst the most threatened taxa globally. Aldabra Atoll, Seychelles, supports significant breeding colonies of seabirds, especially red-footed boobies Sula sula. The population was surveyed by boat during 1968–1969 and in 2000, over which period the population grew from c. 6,500 to 10,000 breeding pairs. In 2022–2023, we monitored five subcolonies across Aldabra to determine breeding phenology and breeding success. In August 2022 and February 2023, we surveyed the atoll-wide population using the boat-based survey methodology followed in earlier studies. We also carried out unmanned aerial vehicle (UAV) surveys in February 2023 to compare the results with the boat-based counts and to quantify inland colonies undetectable by boat. Boat surveys revealed that Aldabra’s red-footed booby population had grown to 36,720 pairs by 2023, an increase that is intrinsically possible based on our population model but only if the much lower count in 2000 was an underestimate. The UAV and boat counts were closely aligned in our study, and aerial images captured a similar number of nests to boat surveys for shoreline colonies. However, UAV surveys revealed several undocumented inland colonies. An additional 5,574 inland breeding pairs of red-footed boobies were counted from images captured inland during aerial surveys in the 2023 wet season, bringing the atoll-wide population to at least 45,817 pairs. We recommend UAVs for surveys of large, conspicuous seabird species at low-lying mangrove colonies. Our study highlights the global importance of Aldabra as the most significant red-footed booby colony in the Indian Ocean and possibly the world.

Invasive rodents severely impact native species, especially on oceanic islands. House mice Mus musculus are known predators of seabird chicks, and there is growing concern about their attacks on adult birds. On sub-Antarctic Marion Island, the single largest breeding site for wandering albatrosses Diomedea exulans, invasive mice, the sole introduced mammal, pose an escalating threat to this Vulnerable species. We report the first direct evidence of mice attacking adult wandering albatrosses, and record mouse attacks on adult wandering albatrosses beyond the localised incidents reported in 2023. Of 2,979 wandering albatross nests counted island-wide in January 2024, 2,295 remained active in April, with 1,102 attended by adults brooding or guarding chicks. Of these, 11 adults (1

The southern oceans are home to a large variety of organisms, including many endemic species. High levels of endemism are due in part to non-physical barriers limiting gene flow in marine species. The sooty albatross Phoebetria fusca is an endangered seabird breeding on seven island groups in Atlantic and Indian Oceans. We sequenced the mitochondrial control region (55 birds) and genotyped 10 microsatellite markers (88 birds) to examine the population genetics of sooty albatrosses from Tristan da Cunha and Gough Island (Atlantic Ocean), and Marion Island, Île de la Possession (Crozet) and Amsterdam Island (Indian Ocean), which together support > 99

Invasive rodents threaten native species in numerous ecosystems, especially oceanic islands. The House Mouse Mus musculus is the only introduced mammal species on sub-Antarctic Gough and Marion Islands. Ample evidence exists of mice preying upon seabird chicks on these two islands, but there have been only a few reports of attacks on adult seabirds, none of which has been fatal. We report the first deaths of adult great albatrosses due to mouse attacks. On Gough Island, three Tristan Albatrosses Diomedea dabbenena (Critically Endangered) brooding small chicks were observed with wounds typical of mouse attacks in March–April 2021; two likely abandoned their chick, causing breeding failure, and the third was found dead eight days after discovery with large blowfly larvae in the wound. On Marion Island, two wounded and eight dead adult Wandering Albatrosses D. exulans (Vulnerable) were found in April 2023. Inspection of the wounded individuals, as well as the injuries on the fresh carcasses strongly suggest that mouse predation was the cause of death. Gough Island is home to virtually all Tristan Albatrosses, and Marion Island is the single most important breeding site for Wandering Albatrosses, home to about a quarter of all breeding birds. The death of breeding adults of these long-lived species emphasizes the urgent need to eradicate introduced mice from these islands.

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.

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.

Ground-nesting birds, such as large gulls and skuas, are known to include a variety of items in their nests as pseudo-eggs, as well as to adopt the eggs of conspecifics or other species. Three hypotheses have been proposed to explain this phenomenon: incubation stimulus, mistaken food, and mistaken egg hypotheses. Of 657 Brown Skua Stercorarius antarcticus nests surveyed on Marion Island during the 2017/18 breeding season, two instances of egg adoption were recorded. Another case of egg adoption was found in a Brown Skua nest on Gough Island in the 2018/19 breeding season. It is likely that all three were cases of mistaken food. This study adds further evidence to the assumption that avian egg predators such as skuas and gulls which are able to steal and carry an egg unbroken in flight, are at risk of this maladaptive behaviour.

The continued decline in the small breeding population of southern elephant seals Mirounga leonina at Gough Island (40°19′S, 9°57′W) over a period of 46 years (1973–2019) signals the likely extirpation of the species at the northernmost extent of its breeding range in the Southern Ocean. The estimated number of births declined from a high (n = 38) in 1975 to a low (n = 2) in 2019, a 95% reduction at an average decrease of 2.15% per annum. The estimated mean time to extinction of this population from a linear regression model is 2 years (95% CI: 0–23 years). This decline is consistent with observed or forecasted population trends of some other marine top predators at the northern extent of their breeding ranges in the Southern Ocean; adding to the prevailing evidence that environmental change is the most plausible hypothesis explaining the range reduction of these marine species limited by a paucity of breeding grounds.

The Tristan da Cunha archipelago comprises three main islands: Tristan, Inaccessible and Nightingale at 37ºS 12ºW, with Gough Island (40ºS 10ºW) the only other temperate oceanic island in the South Atlantic Ocean (Ryan 2007). Tristan and Gough are important breeding sites for 25 species of seabirds (Ryan 2008; Ryan et al. 2014; 2015; Robertson et al. 2016), and a further 30 species of non-breeding seabirds have been reported from the islands (Ryan 2007; Visser et al. 2009; Ryan 2010). We report three additional species from the islands based on observations from 2017 to 2019.

The impacts of invasive house miceMus musculushave 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 FinchRowettia goughensisis 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/km(2)) and wet heath (29.5 birds/km(2)) habitats, compared to coastal tussock (10.9 birds/km(2)) and lowland fern bush habitat (2.6 birds/km(2)). 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.

Pelagic seabirds often nest on islands that are far from productive foraging areas. The Procellariiformes (petrels, shearwaters and albatrosses) are among the longest-ranging seabirds; they have several adaptations that permit them to efficiently utilize distant foraging areas and fast for long periods during incubation (Phillips & Hamer 1999). Giant petrels (Macronectes spp.) are large surface-nesting procellariiforms. They feed both by direct predation and by scavenging carrion, and they are the largest avian predator-scavengers in the Southern Ocean. Among procellariiform seabirds, one partner forages while their mate remains on the nest to incubate their single egg (Warham 1990). Northern giant petrels (Macronectes halli) have incubation shifts lasting up to 17 days (Cooper et al. 2001). In general, incubating procellariiform seabirds do not feed during their shift (Warham 1990). We report the first case to our knowledge of a procellariiform seabird, a northern giant petrel, actively feeding at its nest whilst incubating.

Invasive house mice Mus musculus are significant predators of seabird chicks on islands where they are the only introduced mammal, but there are very few records of attacks on adult birds. We report the first evidence of mouse attacks on adult albatrosses and petrels breeding on Marion and Gough Islands, where there has been a recent increase in attacks on seabird chicks. In September 2017, wounds consistent with a mouse attack were recorded on an incubating adult male Northern Giant Petrel Macronectes halli on Marion Island. The nest was deserted, and breeding success within 500 m was 18% ( n = 11) compared to 68% at nests > 500 m away ( n = 123), suggesting that other incubating adults in the immediate vicinity also might have been affected. In March 2018, an incubating Tristan Albatross Diomedea dabbenena was found on Gough Island with a typical mouse wound on its rump. The egg hatched and the same bird was later seen brooding and feeding the chick. In October 2018, an incubating Atlantic Yellow-nosed Albatross Thalassarche chlororhynchos was found on Gough Island with a wound on its back suggestive of a mouse attack and 23 freshly dead carcasses of this species were found, next to empty nests, in nearby colonies. These observations add to mounting evidence of the impacts of mice on seabirds, and further support calls to eradicate mice from Marion and Gough Islands

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 time-consuming 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 degrees). 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.

Accessible colonies of Grey-headed Albatross Thalassarche chrysostoma chicks on Marion Island have been inspected for chicks presenting mouse wounds from 2015, and during these inspections we found several cases of plumage and bill abnormalities. We report on two cases of leucism and three cases of ‘bent-beak syndrome’ in Grey-headed Albatross chicks, and one case of ‘bent-beak syndrome’ in a Light-mantled Albatross Phoebetria palpebrata chick. The leucistic Grey-headed Albatross chicks were found in 2018 and 2019, and both apparently fledged successfully. Three Grey-headed Albatross chicks with deviated upper mandibles were recorded in 2015, 2018 and 2019, and a single Light-mantled Albatross chick with deviated upper mandible was recorded in a study colony in 2014. None of these chicks survived to fledge. These appear to be the first records of leucism for Grey-headed Albatross, and the first records of bill deformities in any albatross species. Although bill deformities may have been overlooked in the past among Grey-headed and Light-mantled Albatrosses at Marion Island, it is worrying that we have had four records in the last few years. Albatrosses have been intensively studied at many colonies for more than 50 years, and we would have expected previous records of the ‘bent-beak syndrome’ if it occurred naturally at low levels, suggesting a novel threat to these seabirds.

Anomalous pelage colourations have been reported to occur in several pinniped species and can potentially be used to assess gene flow amongst conspecific populations. Aberrant pelage colour has not been documented in sub-Antarctic fur seals Arctocephalus tropicalis older than pups. Sub-Antarctic fur seals were inspected on two of the beaches at Gough Island, South Atlantic Ocean, in the austral summer of 2018/19. A leucistic adult male was sighted on 09 January 2019, the first recorded leucistic individual for the species. Given the apparent extreme rarity of leucism in this sub-Antarctic pinniped species, it is unlikely to contribute to assessment of gene flow amongst conspecific populations.

The order Zoantharia is ubiquitous on the east coast of South Africa, but despite its widespread distribution its species are poorly represented in recent literature from the region. A previous study in this region has shown that Zoanthus natalensis Carlgren, 1938 and Z. durbanensis Carlgren, 1938 are most likely conspecific to the Pacific Z. kuroshio Reimer & Ono, 2006 and Z. vietnamensis Pax & Müller, 1957, respectively. The aims of the present study were to expand on the previous one by conducting a molecular examination of zoantharians found in the intertidal zone along the east coast of South Africa as well as to identify their Symbiodinium symbionts for comparison with conspecifics elsewhere. Symbiodinium identification can be a useful tool when dealing with species that are synonymous as they are likely to share Symbiodinium spp. from the same subclade. The molecular markers mitochondrial 16S ribosomal DNA (mt 16S rDNA), the nuclear internal transcribed spacer region of ribosomal DNA (ITS rDNA), and for the first time on South African zoantharians, the ITS rDNA region for Symbiodinium spp. were used. Seven species were identified. They were Isaurus tuberculatus, Palythoa nelliae, P. tuberculosa, Z. durbanensis, Z. gigantus, Z. natalensis, and Z. sansibaricus. A possible synonymy was found as Palythoa nelliae Pax, 1935 appears to match with the Pacific P. mutuki (Haddon & Shackleton, 1891). Symbiodinium subclade A1 was most often found with Z. natalensis and subclade C15/C91 was most frequently observed in Z. durbanensis. Subclade C1 was found with all Isaurus and Palythoa samples, and with most of Z. sansibaricus samples. Symbiodinium subclades in this study were generally the same as those reported from Indo-Pacific conspecifics.

Eradicating introduced rodents from islands restores these communities, but operations must mitigate bait uptake by non-target species to ensure adequate bait coverage, and minimize mortality of non-target species. Ingestion of toxic bait is a recognised risk for scavenging birds, but is also a concern for generalist feeders. Gough Island, Tristan da Cunha, in the South Atlantic Ocean, has introduced house mice (Mus musculus) that negatively affect the island ecosystem. It is also home to the endemic globally threatened Gough bunting (Rowettia goughensis), a generalist that may be affected by primary poisoning. We presented 26 wild individuals with non-toxic bait pellets and observed their reactions for up to 30 min, or until they flew away. While 23% of Gough buntings did not react to bait pellets, 77% showed some level of interest. Generalist feeders, such as Gough bunting, may also be at risk of primary poisoning during rodent eradication operations.