Roosts are sites that birds repeatedly use and that provide ecological benefits. Many coastal roosting sites for gulls, however, are increasingly being lost or degraded due to land reclamation and human disturbance. This degradation has created a need for gulls to seek alternative roosting opportunities. The province of Jeollanam-do, in South Korea, supports offshore aquaculture, characterized by floating infrastructure that may offer stable resting substrates. We evaluated whether these aquaculture structures function as floating roost sites for the Black-tailed Gull Larus crassirostris and assessed their potential to complement degraded coastal roost habitats. From 2021 to 2024, we tracked 38 adult Black-tailed Gulls using GPS loggers. Roosting behavior was defined as stationary location fixes with a movement speed of 0 km hr(-1). Each roosting fix was initially assigned to a land-cover habitat category and subsequently overlaid with spatial polygons representing aquaculture facilities. We classified fixes according to the corresponding aquaculture category and the underlying land-cover type. Statistical analysis showed that during winter, roosting activity was concentrated on offshore aquaculture structures, particularly floating seaweed farms. In contrast, roosting during spring and summer was dominated by terrestrial and intertidal habitats. Diel patterns differed markedly, with daytime roosting primarily occurring in intertidal habitats and nighttime roosting shifting toward marine waters and floating seaweed farms. Overall, our findings identify offshore aquaculture as a roosting resource for Black-tailed Gulls and highlight an underrecognized ecological function of floating seaweed farms. Managing human disturbance and maintaining floating infrastructure during periods of peak winter use may therefore help sustain roosting opportunities in rapidly changing coastal landscapes.
The Gulf of Maine has extensive potential for floating offshore wind energy development. However, to assess potential impacts, substantial spatiotemporal gaps exist in offshore wildlife data from standardized observational surveys in the region. Such data can support distribution and density modeling to inform marine spatial planning. In an effort to reduce these gaps, we modeled seasonal marine bird densities based on data from four digital aerial surveys conducted in 2023-2024 across a 6,700 km(2) area of the Gulf. We also compared these local models to existing regional density models for marine birds using spatial cross-correlation and center-of-gravity analyses to assess potential mismatches in predictions. Local and regional models were weakly spatially correlated for most taxon/season combinations (global spatial cross-correlation indices with negative exponential decay ranged from-0.21 to 0.23, mean = 0.07, median = 0.11), and local and regional centers of gravity did not consistently align (mean absolute difference = 11.7 km). We discuss several reasons for discrepancies between local and regional predictions of marine bird densities, including underlying differences in model structure and differences in spatiotemporal resolution of source data. Given the limitations of both models, we were unable to determine which model can best inform offshore planning and risk assessments. Further observational surveys are needed to refine models so they may be used reliably for management and conservation, particularly in winter, which is the least surveyed season in the Gulf. Future observational survey efforts should follow best available guidance for survey design to support effective consideration of marine birds in offshore planning and risk assessments.
As glaciers retreat in Antarctica, ice-free areas create new opportunities for seabird colonization and range expansion. Highly mobile species, such as seabirds, can rapidly take advantage of these opportunities by establishing new colonies, but it remains unclear how quickly they can respond and what habitats they prefer. The Gentoo Penguin Pygoscelis papua is one species considered to be a climate change winner, as their populations have increased and they have expanded their range southward amidst rapid climate change along the western coast of the Antarctic Peninsula. Here, we provide a case study at Point 8, Anvers Island, involving satellite-based documentation of glacial retreat, drone-based habitat mapping, and the monitoring of Gentoo Penguin occupation as they colonize newly exposed land. Gentoo Penguins were first observed at Point 8 in the winter of 2019, which coincided with rapid glacial retreat between 2018 and 2020. They nested first in 2020 but did not successfully rear chicks until 2023, following low sea ice years. We hypothesize that Gentoos arrived here as juveniles and began nesting at 2-4 years of age, upon reaching maturity, but did not successfully breed until the age of 5-6 years. The increase in the number of molting adults suggests continuous immigration has been occurring. The time between glacial loss and colonization may suggest the colonization process can happen more quickly than previously thought. Continued sea ice decline and glacial retreat may support further range expansion and colonization by Gentoo Penguins in the study region.
Common Murres Uria aalge are upper trophic-level consumers and useful indicators of the impacts of anomalous climatic events and other perturbations, such as marine heatwaves, long-term change in ocean ecosystems, and changes in predator populations. We used an existing archive of aerial photographs of murre colonies along the coast of Oregon to expand available data on the number of murres nesting in that portion of the California Current ecosystem during 1988-2014. We completed counts of all murre colonies in Oregon ca. every 10 years, developed a stratified random sample of colonies representative of total counts, and completed sample counts ca. every three years. We documented a nearly 25% decline in the number of nesting murres in Oregon, with ca. 97,000 fewer counted in 2014 compared with 1988. Murre numbers declined by 74% (ca. -157,000 murres) along the northern coast of Oregon, increased by 105% (ca. +60,000 murres) along the central coast, and were nearly stable along the southern coast. The centroid of the Oregon breeding population shifted 84.4 km to the south during the study period. Most Oregon breeding colonies experienced growth rates that exceeded the maximum intrinsic growth rate and/or new breeding activity, indicating that philopatry was not strong and large numbers of murres immigrated or recruited from other colonies. Frequent shifts in colony sizes strongly implied substantial movement of murres among colonies throughout the study period, including those colonies on the southern coast where total numbers were stable. Predation and disturbance by Bald Eagles Haliaeetus leucocephalus are known drivers of higher murre mortality rates and lower reproductive success at colonies on the northern and central coasts. The recovering eagle population along the Oregon coast is likely the main factor causing high movement rates of murres among breeding sites, through the "ecology of fear."
Colonially breeding seabirds frequently nest in mixed colonies, which may provide advantages and disadvantages, such as interspecific egg and chick predation. We analyzed egg predation of Elegant Terns Thalasseus elegans and Royal Terns T. maximus by Heermann's Gulls Larus heermanni and Yellow-footed Gulls L. livens at Isla Rasa, in the Gulf of California. All four species nest on this island, including over 90% of the world's Elegant Tern and Heermann's Gull nesting populations. Just a few Yellow-footed Gull pairs nest here, at a ratio of similar to 10,000 Heermann's Gulls:1 Yellow-footed Gull, although their ratio in the study observation area was 10:1. We recorded the number of egg predation attempts, egg predations, and defense attacks by terns on gulls. We analyzed all possible interactions of gulls as predators of tern eggs and found that Yellow-footed Gulls attempted to prey on both tern species' eggs indiscriminately, while Heermann's Gulls preferentially attempted to prey on Elegant Tern eggs. Considered in proportion to their abundance, Yellow-footed Gulls performed significantly more attempts and egg predations on both tern species. For defensive attacks, Royal Terns attacked Yellow-footed Gulls more often than Heermann's Gulls, while the reverse was true for Elegant Terns. Considering their relative numbers, both tern species attacked Yellow-footed Gulls more often than Heermann's Gulls. Our study shows that only a small proportion of Heermann's Gulls engage in tern egg predation, and territorial behavior by both gull species precludes their presence in large numbers around the tern colony. The highest interaction numbers are between Heermann's Gulls and Elegant Terns, the lightest of the four possible gull-tern combinations by mass. Individual Heermann's Gull predations on Elegant Tern eggs were negligible, and considering relative population numbers, we found no significant differences in egg predation by either gull species on either tern species, which may be determining the balance of interactions between these four species at Isla Rasa.
