In coastal Alaska, the nearshore distributions and foraging depths of diving seabirds such as tufted and horned puffins (Fratercula cirrhata and F. corniculata) overlap with salmon set gillnet ("setnet") fisheries. Additive mortality from bycatch in setnets poses a threat to puffin populations that breed in the Kodiak Archipelago of Alaska. We estimated mean annual puffin exposure to setnet bycatch using spatially explicit setnet fishing permit-days and modeled puffin at-sea abundances for the years 1995 to 2021. Using setnet bycatch mortality scenarios based on available fishery observer data, we then simulated population dynamics at Archipelago (regional) and salmon management district (local) scales. Simulations projected extirpation probability across 50 years using mean at-sea abundances from 2002 and 2005 as initial population sizes. Models suggested an increase in 50-year probability of regional extirpation in the Kodiak Archipelago for tufted puffins from 7%, when bycatch mortality was absent, to 33% to 40% in scenarios of 100 to 200 individuals bycaught annually. For horned puffins, 50-year probability of regional extirpation increased from 14%, when bycatch mortality was absent, to 31% to 40% in scenarios of 15 to 30 individuals bycaught annually. Local (district-level) extirpation was >50% probable in most salmon management districts in the Kodiak Archipelago. We conclude that bycatch mitigation for salmon set gillnet fisheries, especially within the Northwest Kodiak District where exposure was greatest, could improve conservation outcomes for puffins. Assessments of exposure and potential mortality for other diving seabird species throughout coastal Alaska may reveal similar population-level impacts.

Dispersal is a fundamental life-history component of species, affecting ecological and evolutionary processes. Sex-specific patterns of dispersal may arise to alleviate the effects of inbreeding, kin competition, or limited resources, and are common in many taxa. We examined sex-biased dispersal of Fratercula arctica (Atlantic Puffin) hatched on Machias Seal Island to 4 breeding colonies in the Gulf of Maine using mark-recapture data. We evaluated if one sex disperses more frequently, if there is a sex bias in the breeding colony choice of dispersed F. arctica, and if sex interacts with other individual factors to influence dispersal. There was no significant difference in the frequency that female and male F. arctica dispersed, or the breeding colony they dispersed to. However, we found that with increasing fledge date, female F. arctica were more likely to disperse and males were less likely to disperse, with this relationship being weaker for male F. arctica. Fledge date was unrelated to body condition, and so other rearing conditions or broader environmental constraints reflected by fledge date may be more influential for females when making dispersal decisions. Our results suggest the smaller Gulf of Maine colonies receive a balanced sex ratio of immigrants from Machias Seal Island, which improves our understanding of metapopulation dynamics. The frequency of dispersal differed among years, and was not fully explained by sex or fledge date, highlighting the need for further research to understand which factors influence F. arctica dispersal. Female and male animals often have different energy requirements, body sizes, and reproductive needs that lead one sex to leave its home to reproduce in a new area (dispersal) more often. In this study, we investigated if there are differences in the patterns of dispersal in female and male Fratercula arctica (Atlantic Puffin) chicks. We found that females and males dispersed from Machias Seal Island similarly often and dispersed to the same islands in the Gulf of Maine to reproduce. However, if female chicks left Machias Seal Island later, they were more likely to disperse to a new island to breed compared to males and females who departed earlier. This was unrelated to body condition, so females may be more sensitive than males to other conditions affecting departure time. Our results show a balanced sex ratio of F. arctica arriving at each island in the Gulf of Maine, which is important for population growth. La dispersion est un & eacute;l & eacute;ment fondamental du cycle vital des esp & egrave;ces qui influe sur les processus & eacute;cologiques et & eacute;volutifs. Des sch & eacute;mas de dispersion sp & eacute;cifiques au sexe peuvent appara & icirc;tre pour att & eacute;nuer les effets de la consanguinit & eacute;, de la comp & eacute;tition entre parents ou de la limitation des ressources, et sont courants chez de nombreux taxons. Nous avons examin & eacute; la dispersion biais & eacute;e selon le sexe d'individus de Fratercula arctica n & eacute;s sur l'& icirc;le Machias Seal vers 4 colonies de reproduction dans le golfe du Maine, en utilisant des donn & eacute;es de marquage-recapture. Nous avons & eacute;valu & eacute; si l'un des sexes se disperse plus fr & eacute;quemment, s'il existe un biais sexuel dans le choix d'une colonie de reproduction des F. arctica dispers & eacute;s, et si le sexe interagit avec d'autres facteurs individuels pour influencer la dispersion. Il n'y avait pas de diff & eacute;rence significative dans la fr & eacute;quence de dispersion des femelles et des m & acirc;les de F. arctica, ni dans la colonie de reproduction vers laquelle ils se dispersaient. Toutefois, nous avons constat & eacute; qu'& agrave; mesure que la date d'envol devenait plus tardive, les femelles de F. arctica & eacute;taient plus susceptibles de se disperser et les m & acirc;les & eacute;taient moins susceptibles de se disperser, et que cette relation & eacute;tait plus faible pour les m & acirc;les de F. arctica. La date d'envol n'& eacute;tait pas reli & eacute;e & agrave; la condition physique; d'autres conditions d'& eacute;levage ou des contraintes environnementales plus larges refl & eacute;t & eacute;es par la date d'envol peuvent avoir plus d'influence sur les femelles lors de la prise de d & eacute;cision de dispersion. Nos r & eacute;sultats sugg & egrave;rent que les plus petites colonies du golfe du Maine re & ccedil;oivent des individus provenant de l'& icirc;le Machias Seal selon un rapport des sexes & eacute;quilibr & eacute;, ce qui am & eacute;liore notre compr & eacute;hension de la dynamique des m & eacute;tapopulations. La fr & eacute;quence de la dispersion variait d'une ann & eacute;e & agrave; l'autre et n'& eacute;tait pas compl & egrave;tement expliqu & eacute;e par le sexe ou la date d'envol, ce qui met en & eacute;vidence le besoin de poursuivre les recherches pour mieux comprendre quels facteurs influencent la dispersion de F. arctica.

The projected growth in offshore wind installations in the northwest Atlantic Ocean is a major issue for conservation biologists interested in marine birds that breed in the region. Biologists often utilize foraging ranges of breeding individuals from their colony to estimate potential conflicts with offshore wind installations. Recent advances in GPS transmitter technology allow biologists to collect high resolution data for moderately-sized (< 200 g) marine birds throughout their breeding and post-breeding stages to quantify movement dynamics. We investigated whether tracking an abundant, generalist species, Common Tern (Sterna hirundo) would be representative of movements of a sympatric endangered specialist, Roseate Tern (Sterna dougalli). From June - September in 2024 and 2025, we used solar-powered GPS transmitters to track breeding and post-breeding movements of adult Common and Roseate Terns nesting on Great Gull Island, New York. We documented high similarity (40–70

The conservation status of Fratercula cirrhata (Tufted Puffin) in the Gulf of Alaska ecosystem, which supports >30-40% of the global population, remains unclear owing to limited or inconsistent monitoring strategies. With similar challenges and less data, the status of the ecologically similar F. corniculata (Horned Puffin) is even less certain. To address these issues, we compiled and analyzed 2 independent long-term datasets collected in the Kodiak Archipelago, Alaska, USA (56-59 degrees N, 151-155 degrees W): (1) 2,121 counts of puffins attending 322 colonies collected from 1975 to 2021 and (2) at-sea densities from 8,954 ship-based transect samples collected during the breeding season from 1975 to 2022. We compared separate joint species distribution models for each survey data type to estimate abundance and long-term trends of F. cirrhata and F. corniculata. Model estimates suggest that the current population (median +/- 95% CI) of F. cirrhata includes 538,435 (+/- 45.4%) individuals at sea and 92,206 (+/- 36.4%) individuals at colonies, representing overall log-linear declines of 50% at sea and 88% at colonies since 1975. Current estimates for F. corniculata include 44,790 (+/- 65.0%) individuals at sea, and 8,165 (+/- 50.4%) individuals at colonies, representing overall log-linear declines of 22% at sea and 67% at colonies since 1975. Parallel trends derived from at-sea and colony surveys, despite measuring different segments of the population, provide strong evidence that both methods can be used effectively to estimate trends of burrow-nesting puffins. Steep declines of both puffin species in the Gulf of Alaska align with declines of other breeding seabirds and point to climate-driven changes in food supplies as likely factors influencing seabird populations in the region.

Vagrancy in birds is an important mechanism contributing to range expansion and the establishment of new breeding populations. However, research on the ecology of vagrant individuals has been limited. From 2005 to 2021, a Red-billed Tropicbird Phaethon aethereus, far outside its usual range, was a summer resident at Seal Island, Maine, USA. In 2020 and 2021, we collected fecal samples from this individual and identified prey types consumed via DNA metabarcoding techniques, using 12S and 18S genes. We identified six fish species in the Redbilled Tropicbird fecal DNA samples, with Atlantic Saury Scomberesox saurus and Atlantic Mackerel Scomber scombrus contributing similar to 75% of DNA reads. To our knowledge, these two species have not previously been documented in the diet of Red-billed Tropicbirds, yet they were important in both years despite contrasting environmental conditions. Although it is quite possible that this vagrant individual had not encountered either saury or mackerel prior to its extralimital dispersal to the Gulf of Maine, these species share morphological and functional traits with known tropicbird prey elsewhere. Thus, despite occurring > 2,400 km from known breeding sites, this Red-billed Tropicbird was capable of selecting suitable prey in a variable environment.

miniaturization of solar-powered satellite trackers has allowed for the collection of high-resolution seabird movement data, but descriptions of the non-breeding movements of smaller-bodied species remain poorly represented in the literature. We analyzed satellite data collected from Gulf of Maine-breeding Common Terns (Sterna hirundo) to explore non-breeding movement behavior. Ten individuals were tagged at their colonies with Global Positioning System or Argos Platform Terminal Transmitter tags. Four tags provided the first full satellite-derived migration cycle tracks published for coastally breeding Common Terns, while additional tags provided partial tracks. Important stopover locations included Cape Cod, Massachusetts, Chesapeake Bay, Delaware, and Cape Hatteras, North Carolina, and overwintering locations included the Suriname coast and the Amazon River outflow system. Analyses of flight dynamics showed that speeds were elevated during the northbound migration period, the duration of which was less than half that of the southbound migration period. Highly spatiotemporally resolved data from a sub-analysis of one GPS tag found that flight speeds and altitudes recorded were also elevated during dark hours. Our results detail the space use and movement behavior of Common Terns across the full non-breeding cycle, which is critical for informing conservation efforts in the face of impacts from anthropogenic infrastructure, pollution, and climate change. Received 1 Nov 2024, accepted 30 Sept 2025.

The Aleutian tern (Onychoprion aleuticus) is a species of high conservation concern in Alaska, USA, owing to large declines at known breeding locations since the 1960s. The small population size and ephemeral behavior of this species have limited the collection of basic biological information and hindered the identification of potential drivers of this decline. Significant unknowns include the factors, and their relative importance, influencing nest survival. To investigate these questions, we estimated daily nest survival (DNS) for 148 nests from 5 breeding colonies during 2017 to 2020 in the Kodiak Archipelago, Alaska with 105 monitored using remote cameras. We used the nest survival model in program MARK to estimate DNS rates as a function of colony location, year, within-season time trends, vegetation cover and height, and 6 daily weather covariates. Our top model suggested that DNS rates increased with vegetation height, decreased as the season progressed, and included a significant interaction between year and colony. Average nest success (i.e., percent chance that a nest survived to hatch) over the 22-day incubation period varied by colony but was generally very low, averaging 1.2% (95% CI = 0-11%) in 2017-2018 to 14% (95% CI = 0.1-38%) in 2019-2020 across all colonies. The importance of year in the model suggests that a large-scale annual driver, like food availability, may have played an important role in this species' breeding success. A severe marine heatwave was present in the Gulf of Alaska during 2014-2016 and our results suggest that some effects of this anomalous event, such as reduced prey availability, lingered even after temperatures returned to normal. Additionally, the variation in DNS across colony locations indicated that local factors, such as predation pressure, may also drive significant variation in Aleutian tern productivity. These findings suggest that a combination of local factors and climate change may be important drivers of the >90% decline in Alaska's breeding population of Aleutian terns.

We observed a family of Atlantic Puffins Fratercula arctica in a burrow on Seal Island National Wildlife Refuge in the Gulf of Maine, USA, during the 2017-2020 and 2022 breeding seasons. The burrow was equipped with a high-resolution web camera, which allowed 24-hour daily observations. We investigated the impacts of elevated sea surface temperature (SST) and marine heatwaves (MHWs), which are linked to low food availability, on chick provisioning and burrow attendance. In 2017, 2019, 2020, and 2022, the female was the primary provisioner, providing twice as many feedings as the male, and the male was the primary burrow guardian, spending twice as much time at the burrow as the female. Using generalized linear models to estimate relationships between SST, feeding rates, and burrow attendance, we found that higher SST was associated with lower feeding rates and burrow attendance. These impacts were amplified in 2018 amid a prolonged MHW. The puffins struggled to find food consistently, leading to lower provisioning rates, smaller bill-loads of mostly low-quality prey, and a visibly under-nourished chick. This prompted the male to trade his burrow-guarding role for additional chick provisioning, and the chick fledged after 69 days, 28 days longer than is typical. This study is the first to demonstrate that Atlantic Puffins can modify their usual parenting roles in response to prey availability, deferring migration and extending chick-rearing by as many as four weeks. We also observed modification in chick behavior amid a high-intensity MHW in 2022, during which the chick was frequently provisioned with American Butterfish Peprilus triacanthus, a deep-bodied fish that is not easily swallowed. The chick consistently consumed butterfish piecemeal, pulling off and swallowing small pieces, until the remaining portion was small enough to be swallowed. This was an effective strategy and a behavior that has not previously been reported.

In 2017 and 2018, satellite transmitters were deployed (n2017 = 13, n2018 = 14) on Aleutian Terns Onychoprion aleuticus in two areas of Alaska, USA, to investigate breeding season movements and temporal patterns of colony activity. The effort was intended to aid in the development of a large-scale population-assessment framework. Across the two years, we observed dispersal to seven confirmed or potential (putative) colonies, none of which were previously documented, ranging in distance from 0.4 to 64.2 km from tag deployment sites. Although most terns did not associate with any known colonies during the breeding season, several individuals from the study area in western Alaska were sequentially associated with multiple colonies. Breeding season movements were usually within tens of kilometers of the capture location, but movements of several hundred kilometers were recorded occasionally. These results should be interpreted cautiously because we do not know the post-tagging nesting status of marked terns, nor were we able to determine whether there were tern behavioral changes related to capture and tagging. With this caution in mind and based on our findings, we recommend that future efforts to estimate total Aleutian Tern population sizes or trends consider the following: (1) estimates should not rely solely upon surveys of previously documented colonies; (2) estimation procedures should account for the potential movement of individual terns among colonies, the possible lack of association of a tern with any colony, the possible association of a tern with multiple colonies, and/or the possibility that adults do not attempt to breed each year; and (3) if necessary, studies should survey subsets of the Alaska breeding range in successive years to reduce the uncertainty around the size of the statewide tern population.

Incorporating predator-prey information in fisheries stock assessments is challenging due to the multitude, complexity, and dynamic nature of trophic interactions. However, integrating indices of abundance derived from predator diet data into assessment models as proxy abundance indices of poorly sampled age classes may have utility as an ecosystem approach that improves assessment outcomes. Here, we leveraged 34 years of observations of common terns (Sterna hirundo) provisioning age-1 Atlantic herring (Clupea harengus) to their chicks across 12 islands in the Gulf of Maine to construct an annual index of herring provisioning rates. We then integrated this index into a state-space, age-structured assessment model as an index for age-1 Atlantic herring (recruit) abundance. Our results showed that when the assessment model was fit assuming a linear relationship between the herring provisioning index and recruitment, the model produced a residual pattern indicating a non-linear response between the provisioning of Atlantic herring and their abundance in the environment. These findings suggested that Atlantic herring provisioning rates plateaued during periods of high recruitment (satiation) and remained consistent at low levels during periods of low recruitment (hyperstability). Allowing for this non-linearity in the stock assessment improved the fit to the index. Ultimately, the seabird diet index may be a useful indicator to incorporate into the Atlantic herring assessment process; however, the quantitative incorporation of this index into the assessment model is challenged by non-linear predator-prey dynamics.

Predation by Caspian terns Hydroprogne caspia is a factor limiting the recovery of some Endangered Species Act‐listed populations of salmonids from the Columbia River basin, especially steelhead Oncorhynchus mykiss . This prompted the development and implementation of two separate management plans, one in the Columbia River estuary and the other in the Columbia Plateau region, to reduce the impact of Caspian tern predation on smolt survival. Caspian terns nesting at managed breeding colonies within the basin were relocated to alternative nesting islands created for terns outside the basin. Both plans were successful in significantly reducing smolt losses to Caspian terns nesting at managed sites; however, new developments have led to regression in smolt survival gains associated with tern management. Adaptive management to prevent terns at managed colonies from relocating to nest elsewhere in the basin and to improve nesting opportunities for Caspian terns outside the basin are needed to maximize the survival benefits to Endangered Species Act‐listed salmonids from management. Adaptive management is also necessary to ensure the long‐term viability of the Pacific Flyway population of Caspian terns, whose breeding population has declined by more than 50% since the two management plans were implemented.

Atlantic puffin ( Fratercula arctica , hereafter “puffin”) reproductive success in the Gulf of Maine (GoM) has decreased following a recent oceanographic regime shift and subsequent rapid warming. Concurrent changes in both the regional forage fish community and puffin chick diet and provisioning rates suggest that inadequate prey resources may be driving this decline. To determine what prey GoM puffins were feeding on during two years of marine heatwave conditions, we assessed puffin diet using two methods: traditional, observational methods that utilize bill-load photography and emerging methods employing fecal DNA metabarcoding. We identified a strong correlation between the composition of chick diet as estimated through traditional and emerging methods, supporting the interpretation of DNA relative read abundance as a quantitative metric of diet composition. Both methods identified the same dominant prey groups, but metabarcoding identified a greater number of species and offered higher taxonomic resolution. Puffin adults and chicks fed on many of the same prey types, although adults consumed a greater variety of taxa and consumed more low quality prey than they provisioned chicks, as predicted by optimal foraging theory. For both age classes, diet varied both between and within years, likely reflecting changes in the local forage fish community in response to environmental variability. During these two years of marine heatwave conditions, puffins exploited unusual abundances of typically-uncommon prey, yet low puffin productivity suggests the observed dietary plasticity was not able to compensate for apparent prey shortages. Continued refinement of molecular tools and the interpretation of the data they provide will enable better assessments of how seabirds of diverse ages and breeding stages are compensating for changing forage fish communities in response to global climate change. ### Competing Interest Statement The authors have declared no competing interest.

IntroductionAtlantic puffin (Fratercula arctica, hereafter “puffin”) reproductive success in the Gulf of Maine (GoM) has declined following a recent oceanographic regime shift that has led to rapid warming and increasingly frequent marine heatwaves. Concurrent changes in both the regional forage fish community and puffin chick diets and provisioning rates suggest that inadequate prey resources may be driving this decline. Traditional, noninvasive methods of diet assessment, however, are unable to determine seabird diet at many age classes and breeding stages.MethodsTo determine what prey GoM puffins were feeding on during two years of marine heatwave conditions, we assessed puffin diet using two complementary methods: traditional, observational methods that utilize bill-load photography and emerging methods employing fecal DNA metabarcoding. We then examined the effect of methodology, age, breeding stage, and year on puffin diet composition. ResultsWe identified a strong correlation between the composition of chick diet as estimated through traditional and emerging methods, supporting the interpretation of DNA relative read abundance as a quantitative metric of diet composition. Both methods identified the same dominant prey groups yet metabarcoding identified a greater number of species and offered higher taxonomic resolution. Additionally, metabarcoding revealed adult puffin diet during the incubation period for the first time. Although puffin adults and chicks fed on many of the same prey types, adults consumed a greater variety of taxa and consumed more low quality prey types than they provisioned chicks.DiscussionFor both age classes, diet varied both between and within years, likely reflecting changes in the local forage fish community in response to environmental variability. Puffins exploited unusual abundances of typically-uncommon prey during these two years of marine heatwave conditions, yet low puffin productivity suggests the observed dietary plasticity was not fully able to compensate for apparent prey shortages. Continued refinement of molecular methods and the interpretation of the data they provide will enable better assessments of how seabirds of diverse ages and breeding stages are adapting to changing prey communities.

Compared to other animal movements, prospecting by adult individuals for a future breeding site is commonly overlooked. Prospecting influences the decision of where to breed and has consequences on fitness and lifetime reproductive success. By analysing movements of 31 satellite- and GPS-tracked gull and tern populations belonging to 14 species in Europe and North America, we examined the occurrence and factors explaining prospecting by actively breeding birds. Prospecting in active breeders occurred in 85.7% of studied species, across 61.3% of sampled populations. Prospecting was more common in populations with frequent inter-annual changes of breeding sites and among females. These results contradict theoretical models which predict that prospecting is expected to evolve in relatively predictable and stable environments. More long-term tracking studies are needed to identify factors affecting patterns of prospecting in different environments and understand the consequences of prospecting on fitness at the individual and population level.

The global loss of biodiversity has inspired actions to restore nature across the planet. Translocation and social attraction actions deliberately move or lure a target species to a restoration site to reintroduce or augment populations and enhance biodiversity and ecosystem resilience. Given limited conservation funding and rapidly accelerating extinction trajectories, tracking progress of these interventions can inform best practices and advance management outcomes. Seabirds are globally threatened and commonly targeted for translocation and social attraction (“active seabird restoration”), yet no framework exists for tracking these efforts nor informing best practices. This study addresses this gap for conservation decision makers responsible for seabirds and coastal management. We systematically reviewed active seabird restoration projects worldwide and collated results into a publicly accessible Seabird Restoration Database. We describe global restoration trends, apply a systematic process to measure success rates and response times since implementation, and examine global factors influencing outcomes. The database contains 851 active restoration events in 551 locations targeting 138 seabird species; 16% of events targeted globally threatened taxa. Visitation occurred in 80% of events and breeding occurred in 76%, on average 2 y after implementation began (SD = 3.2 y). Outcomes varied by taxonomy, with the highest and quickest breeding response rates for Charadriiformes (terns, gulls, and auks), primarily with social attraction. Given delayed and variable response times to active restoration, 5 y is appropriate before evaluating outcomes. The database and results serve as a model for tracking and evaluating restoration outcomes, and is applicable to measuring conservation interventions for additional threatened taxa.

We reviewed studies of piscivorous colonial waterbird predation on juvenile salmonids to synthesize current knowledge of factors affecting fish susceptibility to avian predators. Specifically, we examined peer-reviewed publications and reports from academic, governmental, and nongovernmental agencies to identify commonalities and differences in susceptibility of salmonids to avian predation, with a focus on mark-recovery studies in the Columbia River basin. Factors hypothesized to influence salmonid susceptibility to avian predation were grouped into four general categories: (1) salmonid species and populations, (2) environmental factors, (3) prey density, predator density, and migration timing, and (4) prey characteristics. Our review focused on predation by Caspian terns Hydroprogne caspia, double-crested cormorants Nannopterum auritum, and gull species Larus spp. as these are the most well-studied avian predators of salmonids. Results indicated that predator-prey interactions varied across salmonid species and populations and species of avian predator. Inferences across studies supported multiple hypotheses regarding predator-prey dynamics, including environmental factors that influence prey exposure to predators (e.g., river flows, turbidity, alternative prey), variation in predator and prey abundances, predator characteristics (e.g., foraging behavior, colony location), and prey characteristics (e.g., fish length, condition). Mark-recovery studies of avian predation on fish populations have greatly improved our understanding of the factors affecting fish susceptibility to avian predation, the relative contributions of abiotic and biotic factors to predation susceptibility, and the extent to which avian predation affects fish survival and the viability of prey populations. Future studies that jointly model predation and survival and the factors affecting those processes will further broaden our understanding of predator-prey dynamics and directly evaluate the effects of predation on prey population dynamics.

In 2013 and 2014, multiple field excursions of varying scope were concentrated on the Columbia River, a highly energetic, partially mixed estuary. These experiments included surface drifter and synthetic aperture radar (SAR) measurements during the ONR RIVET-II experiment, and a novel animal tracking effort that samples oceanographic data by employing cormorants tagged with biologging devices. In the present work, several different data types from these experiments were combined in order to test an iterative, ensemble-based inversion methodology at the mouth of the Colum-bia River (MCR). Results show that, despite inherent limitations of observation and model accuracy, it is possible to detect dynamically relevant bathymetric features such as large shoals and channels while originating from a linear, featureless prior bathymetry in a partially mixed estuary by inverting surface current and gravity wave observations with a 3D hydro-static ocean model. Bathymetry estimation skill depends on two factors: location (i.e., differing estimation quality inside versus outside the MCR) and observation type (e.g., surface currents versus significant wave height). Despite not being inverted directly, temperature and salinity outputs in the hydrodynamic model improved agreement with observations after bathymetry inversion.

To identify potential threats and prioritize areas for protection, modern conservation efforts rely on spatial data. While it is often impossible to study the movements of entire populations, we can examine patterns among individuals and groups to better understand populations as a whole. We used geolocator tags to determine where Atlantic Puffins (Fratercula arctica) at the southern edge of their range, vulnerable to warming waters and anthropogenic influence, spend the nonbreeding season, and whether birds from different colonies or parts of the same colony used different overwintering strategies. Between 2013 and 2017, tags were deployed on 97 puffins breeding on three islands in the Gulf of Maine: Machias Seal Island, Matinicus Rock, and Seal Island National Wildlife Refuge. Most tagged puffins remained in or near the Gulf of Maine throughout the autumn and early winter months, venturing as far south as Cape Hatteras (ca. 35 degrees N) in February, March, and April, before returning to their respective colonies. Three individuals travelled north to the Gulf of St. Lawrence and waters around Newfoundland immediately after breeding, returning to the Gulf of Maine in mid-winter. We found no evidence of inter- or intra-colony differences in overwinter movement. This is the first study focusing on overwinter movements of puffins breeding at the southern edge of their range in North America and can assist in the development of policy regarding management and protection of important marine areas for puffins and other species. Received 23 Jun 2021, accepted 17 Jul 2022.

The diet of two piscivorous bird species nesting in the lower Columbia River was compared with purse seine samples of the fish community to explore the influence of alternative prey availability on the consumption of juvenile salmonids in the Columbia River Estuary. The composition of Caspian tern (CATE) and double-crested cormorant (DCCO) diets broadly overlapped with each other and with independent purse seine sampling. However, consistent seasonal differences were observed in the mass of salmonid and marine forage fish prey in net sampling and the diets of piscivorous birds; Caspian terns had a higher proportion of salmonids in their diets than did cormorants or net sampling across seasons in all years. Caspian terns responded nonlinearly to the availability of marine forage fish, with the proportion of juvenile salmonids in their diet significantly declining when the proportion of marine prey species available exceeded a threshold of 48%. In contrast, cormorants showed a weak, linear response in this relationship. These results demonstrate how temporal variation in one prey type (marine forage fish that enter the estuary later in summer) can indirectly reduce consumption of another prey type (juvenile salmonids) by a common predator (piscivorous birds)—an apparent mutualism. This work shows the importance of understanding the broader food web. Developing management strategies that account for avian predator response to variation in the prey fish community will be important for increasing the survival of threatened and endangered salmonids in a changing environment.