Temperature synchronizes temporal variation in laying dates across European hole-nesting passerines.

Identifying the environmental drivers of variation in fitness-related traits is a central objective in ecology and evolutionary biology. Temporal fluctuations of these environmental drivers are often synchronized at large spatial scales. Yet, whether synchronous environmental conditions can generate spatial synchrony in fitness-related trait values (i.e., correlated temporal trait fluctuations across populations) is poorly understood. Using data from long-term monitored populations of blue tits (Cyanistes caeruleus, n = 31), great tits (Parus major, n = 35), and pied flycatchers (Ficedula hypoleuca, n = 20) across Europe, we assessed the influence of two local climatic variables (mean temperature and mean precipitation in February-May) on spatial synchrony in three fitness-related traits: laying date, clutch size, and fledgling number. We found a high degree of spatial synchrony in laying date but a lower degree in clutch size and fledgling number for each species. Temperature strongly influenced spatial synchrony in laying date for resident blue tits and great tits but not for migratory pied flycatchers. This is a relevant finding in the context of environmental impacts on populations because spatial synchrony in fitness-related trait values among populations may influence fluctuations in vital rates or population abundances. If environmentally induced spatial synchrony in fitness-related traits increases the spatial synchrony in vital rates or population abundances, this will ultimately increase the risk of extinction for populations and species. Assessing how environmental conditions influence spatiotemporal variation in trait values improves our mechanistic understanding of environmental impacts on populations.

Foraging range scales with colony size in high-latitude seabirds.

Density-dependent prey depletion around breeding colonies has long been considered an important factor controlling the population dynamics of colonial animals.1-4 Ashmole proposed that as seabird colony size increases, intraspecific competition leads to declines in reproductive success, as breeding adults must spend more time and energy to find prey farther from the colony.1 Seabird colony size often varies over several orders of magnitude within the same species and can include millions of individuals per colony.5,6 As such, colony size likely plays an important role in determining the individual behavior of its members and how the colony interacts with the surrounding environment.6 Using tracking data from murres (Uria spp.), the world's most densely breeding seabirds, we show that the distribution of foraging-trip distances scales to colony size0.33 during the chick-rearing stage, consistent with Ashmole's halo theory.1,2 This pattern occurred across colonies varying in size over three orders of magnitude and distributed throughout the North Atlantic region. The strong relationship between colony size and foraging range means that the foraging areas of some colonial species can be estimated from colony sizes, which is more practical to measure over a large geographic scale. Two-thirds of the North Atlantic murre population breed at the 16 largest colonies; by extrapolating the predicted foraging ranges to sites without tracking data, we show that only two of these large colonies have significant coverage as marine protected areas. Our results are an important example of how theoretical models, in this case, Ashmole's version of central-place-foraging theory, can be applied to inform conservation and management in colonial breeding species.

Differences in Trophic Level, Contaminant Load, and DNA Damage in an Urban and a Remote Herring Gull (Larus argentatus) Breeding Colony in Coastal Norway.

Herring gulls (Larus argentatus) are opportunistic feeders, resulting in contaminant exposure depending on area and habitat. We compared contaminant concentrations and dietary markers between two herring gull breeding colonies with different distances to extensive human activity and presumed contaminant exposure from the local marine diet. Furthermore, we investigated the integrity of DNA in white blood cells and sensitivity to oxidative stress. We analyzed blood from 15 herring gulls from each colony-the urban Oslofjord near the Norwegian capital Oslo in the temperate region and the remote Hornøya island in northern Norway, on the Barents Sea coast. Based on d13 C and d34 S, the dietary sources of urban gulls differed, with some individuals having a marine and others a more terrestrial dietary signal. All remote gulls had a marine dietary signal and higher relative trophic level than the urban marine feeding gulls. Concentrations (mean ± standard deviation [SD]) of most persistent organic pollutants, such as polychlorinated biphenyl ethers (PCBs) and perfluorooctane sulfonic acid (PFOS), were higher in urban marine (PCB153 17 ± 17 ng/g wet weight, PFOS 25 ± 21 ng/g wet wt) than urban terrestrial feeders (PCB153 3.7 ± 2.4 ng/g wet wt, PFOS 6.7 ± 10 ng/g wet wt). Despite feeding at a higher trophic level (d15 N), the remote gulls (PCB153 17 ± 1221 ng/g wet wt, PFOS 19 ± 1421 ng/g wet wt) were similar to the urban marine feeders. Cyclic volatile methyl siloxanes were detected in only a few gulls, except for decamethylcyclopentasiloxane in the urban colony, which was found in 12 of 13 gulls. Only hexachlorobenzene was present in higher concentrations in the remote (2.6 ± 0.42 ng/g wet wt) compared with the urban colony (0.34 ± 0.33 ng/g wet wt). Baseline and induced DNA damage (doublestreak breaks) was higher in urban than in remote gulls for both terrestrial and marine feeders. Environ Toxicol Chem 2022;41:2466-2478. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

The relationship between daily behavior, hormones, and a color dimorphism in a seabird under natural continuous light.

The predictable oscillation between the light of day and the dark of night across the diel cycle is a powerful selective force that has resulted in anticipatory mechanisms in nearly all taxa. At polar latitude, however, this oscillation becomes highly attenuated during the continuous light of polar day during summer. A general understanding of how animals keep time under these conditions is poorly understood. We tested the hypothesis that the common murre (a seabird, Uria aalge) can use melatonin and corticosterone, hormones associated with timekeeping, to track the diel cycle despite continuous light. We also tested the assumption that common murres breeding during polar summer schedule their colony attendance by time of day and sex, as they do at subpolar latitude. In the Atlantic population, common murres have a plumage color dimorphism associated with fitness-related traits, and we investigated the relationship of this dimorphism with colony attendance, melatonin, and corticosterone. The common murres did not schedule their attendance behavior by time of day or sex, yet they had higher concentrations of melatonin and, to a more limited extent, corticosterone during "night" than "day". Melatonin also linked to behavioral state. The two color morphs tended to have different colony-attendance behavior and melatonin concentrations, lending support for balancing selection maintaining the plumage dimorphism. In common murres, melatonin can signal time of day despite continuous light, and the limited diel variation of corticosterone contributes to the mounting evidence that polar-adapted birds and mammals require little or no diel variation in circulating glucocorticoids during polar day.

Seasonal variation of mercury contamination in Arctic seabirds: A pan-Arctic assessment.

Mercury (Hg) is a natural trace element found in high concentrations in top predators, including Arctic seabirds. Most current knowledge about Hg concentrations in Arctic seabirds relates to exposure during the summer breeding period when researchers can easily access seabirds at colonies. However, the few studies focused on winter have shown higher Hg concentrations during the non-breeding period than breeding period in several tissues. Hence, improving knowledge about Hg exposure during the non-breeding period is crucial to understanding the threats and risks encountered by these species year-round. We used feathers of nine migratory alcid species occurring at high latitudes to study bird Hg exposure during both the breeding and non-breeding periods. Overall, Hg concentrations during the non-breeding period were ~3 times higher than during the breeding period. In addition, spatial differences were apparent within and between the Atlantic and Pacific regions. While Hg concentrations during the non-breeding period were ~9 times and ~3 times higher than during the breeding period for the West and East Atlantic respectively, Hg concentrations in the Pacific during the non-breeding period were only ~1.7 times higher than during the breeding period. In addition, individual Hg concentrations during the non-breeding period for most of the seabird colonies were above 5 µg g-1 dry weight (dw), which is considered to be the threshold at which deleterious effects are observed, suggesting that some breeding populations might be vulnerable to non-breeding Hg exposure. Since wintering area locations, and migration routes may influence seasonal Hg concentrations, it is crucial to improve our knowledge about spatial ecotoxicology to fully understand the risks associated with Hg contamination in Arctic seabirds.

Persistent organic pollution in a high-Arctic top predator: sex-dependent thresholds in adult survival.

In long-lived species, any negative effect of pollution on adult survival may pose serious hazards to breeding populations. In this study, we measured concentrations of various organochlorines (OCs) (polychlorinated biphenyl and OC pesticides) in the blood of a large number of adult glaucous gulls (Larus hyperboreus) breeding on Bjørnøya (Bear Island) in the Norwegian Arctic, and modelled their local survival using capture-recapture analysis. Survival was negatively associated with concentrations of OCs in the blood. The effect of OCs was nonlinear and evident only among birds with the highest concentrations (the uppermost deciles of contamination). The threshold for depressed survival differed between the sexes, with females being more sensitive to contamination. For birds with lower OC concentration, survival was very high, i.e. at the upper range of survival rates reported from glaucous and other large gull species in other, presumably less contaminated populations. We propose two non-exclusive explanations. First, at some threshold of OC concentration, parents (especially males) may abandon reproduction to maximize their own survival. Second, high contamination of OC may eliminate the most sensitive individuals from the population (especially among females), inducing a strong selection towards high-quality and less sensitive phenotypes.