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Understanding the habitat use of individuals can facilitate methods to measure the degree to which populations will be affected by potential stressors. Such insights can be hard to garner for marine species that are inaccessible during phases of their annual cycles. Here, we quantify the link between foraging habitat and behaviour in an aquatic bird of high conservation concern, the red‐throated diver (Gavia stellata) across three breeding populations (Finland, Iceland and Scotland) during their understudied moult period. Specifically, we quantify the relationship between feather isotope values (δ13C and δ15N) and diving behaviour, within and between populations, examining the use of intra‐depth zone (IDZ) dives as a proxy for benthic foraging. We found a strong positive relationship between both higher δ15N values and, to a lesser extent, δ13C values and the proportion of IDZ dives. This relationship was consistent across all three populations, but the baseline δ13C values varied between them, indicative of the populations' different moulting areas. Our results demonstrate that red‐throated divers continue to be generalist foragers after their breeding seasons, and that behavioural flexibility varies within and between populations. Furthermore, due to the existence of these relationships, we reveal the potential of stable isotope analysis as a standalone tool for monitoring changes in habitat use in this ecologically significant species. The approach may also apply to other generalist foragers that are known to use multiple foraging strategies (e.g., foraging benthically and pelagically), with implications for future conservation efforts. [ABSTRACT FROM AUTHOR]

The island of Taiwan, with its diverse microclimates and key position on the East Asian-Australasian Flyway, attracts numerous bird enthusiasts due to its diverse avian fauna. Nevertheless, due to the scarcity of fossil records, there is a significant knowledge gap between modern and ancient avifaunas in Taiwan. Currently, there is only a single described Pleistocene fossil; it is attributed to Phasianidae. To address this gap, this study describes two new bird fossils, a left humerus and a left tibiotarsus, and discusses them in detail herein. The fossils were collected from the Liuchungchi Formation (Early Pleistocene, 1.95–1.35 Ma) in Niubu, Chiayi, southwestern Taiwan, which represents a neritic environment. The fossils are identified as from species of Gaviidae (loons), with the humerus belonging to an undetermined species of Gavia and the tibiotarsus to Gavia stellata. Loons are seabirds that are primarily distributed in high- and middle latitudes of the Northern Hemisphere. In addition, these birds are extremely rare in modern Taiwan: records are scarce and most are limited to northern and northeastern Taiwan since the 1860s, indicating that the modern Gavia birds only occasionally visit Taiwan. All known Pleistocene fossils of species of Gavia from the northern West Pacific come from Japan. The Taiwan fossils of Gavia provide valuable bird evolutionary and paleobiogeographic information for the subtropical West Pacific and may imply the presence of a distinct avifauna in the region during the Early Pleistocene.

Migratory species have geographically separate distributions during their annual cycle, and these areas can vary between populations and individuals. This can lead to differential stress levels being experienced across a species range. Gathering information on the areas used during the annual cycle of red‐throated divers (RTDs; Gavia stellata) has become an increasingly pressing issue, as they are a species of concern when considering the effects of disturbance from offshore wind farms and the associated ship traffic. Here, we use light‐based geolocator tags, deployed during the summer breeding season, to determine the non‐breeding winter location of RTDs from breeding locations in Scotland, Finland, and Iceland. We also use δ15N and δ13C isotope signatures, from feather samples, to link population‐level differences in areas used in the molt period to population‐level differences in isotope signatures. We found from geolocator data that RTDs from the three different breeding locations did not overlap in their winter distributions. Differences in isotope signatures suggested this spatial separation was also evident in the molting period, when geolocation data were unavailable. We also found that of the three populations, RTDs breeding in Iceland moved the shortest distance from their breeding grounds to their wintering grounds. In contrast, RTDs breeding in Finland moved the furthest, with a westward migration from the Baltic into the southern North Sea. Overall, these results suggest that RTDs breeding in Finland are likely to encounter anthropogenic activity during the winter period, where they currently overlap with areas of future planned developments. Icelandic and Scottish birds are less likely to be affected, due to less ship activity and few or no offshore wind farms in their wintering distributions. We also demonstrate that separating the three populations isotopically is possible and suggest further work to allocate breeding individuals to wintering areas based solely on feather samples. [ABSTRACT FROM AUTHOR]

Differing environmental conditions can have profound effects on many behaviours in animals, especially where species have large geographic ranges. Seasonal changes or progression through life history stages impose differential constraints, leading to changes in behaviours. Furthermore, species which show flexibility in behaviours, may have a higher capacity to adapt to anthropogenic-induced changes to their environment. The red-throated diver (RTD) is an aquatic bird, that is able to forage in both freshwater and marine environments, though little else is known about its behaviours and its capacity to adapt to different environmental conditions. Here, we use timedepth recorders and saltwater immersion loggers to examine the foraging behaviour of RTDs from three regions across northwest Europe. We found that in the breeding season, birds from two regions (Iceland and Scotland) foraged in the marine environment, while birds from Finland, foraged predominantly in freshwater. Most of the differences in diving characteristics were at least partly explained by differences in foraging habitat. Additionally, while time spent foraging did not change through the breeding season, dives generally became more pelagic and less benthic over the season, suggesting RTDs either switched prey or followed vertical prey movements, rather than increasing foraging effort. There was a preference for foraging in daylight over crepuscular hours, with a stronger effect at two of the three sites. Overall, we provide the first investigation of RTD foraging and diving behaviour from multiple geographic regions and demonstrate variation in foraging strategies in this generalist aquatic predator, most likely due to differences in their local environment. [ABSTRACT FROM AUTHOR]

Much of the Laurentian Great Lakes region is a mercury-sensitive landscape, in which atmospheric deposition and waterborne sources of mercury (Hg) have led to high concentrations of bioavailable methylmercury (MeHg) in predatory fish and piscivorous wildlife. Efforts since the early 1990s have established the common loon ( Gavia immer) as the primary avian indicator for evaluating the exposure and effects of MeHg in North America. A regional Hg dataset was compiled from multiple loon tissue types and yellow perch ( Perca flavescens), a preferred prey fish species for loons. Hg exposure in loons and perch was modeled to develop male and female loon units (MLU and FLU, respectively), standardized metrics that represent the estimated blood Hg exposure of a male or female loon for a given loon territory or water body. Using this common endpoint approach to assess loon Hg exposure, the authors demonstrate spatial trends in biotic Hg concentrations, examine MeHg availability in aquatic ecosystems of the Great Lakes region in relation to landscape-level characteristics, and identify areas with potentially significant adverse reproductive impacts to loons and other avian piscivores. Based on 8,101 MLUs, seven biological Hg hotspots were identified in the Great Lakes region. Policy-relevant applications are presented. [ABSTRACT FROM AUTHOR]