Foraging areas, offshore habitat use, and colony overlap by incubating Leach's storm-petrels Oceanodroma leucorhoa in the Northwest Atlantic

Exposure of an endangered seabird species to persistent organic pollutants: Assessing levels in blood and link with reproductive parameters

Ocean contamination, particularly from persistent organic pollutants (POPs), remains a significant threat to marine predators that occupy high trophic positions. Long-lived procellariform seabirds are apex predators in marine ecosystems and tend to accumulate contaminants. Prolonged exposure to pollutants negatively affects their fitness including reproductive success. Low breeding success may represent a hurdle for the restoration of small and endangered seabird populations, including several highly threatened gadfly petrels. Here we investigated the annual variation (2019 and 2022) in organochlorine pesticide (OCP), polychlorinated biphenyl ether (PCB), polybrominated diphenyl ether (PBDE), and polycyclic aromatic hydrocarbon (PAH) exposure in the endangered Bermuda petrel (Pterodroma cahow), and the relationship between female contaminant burden and breeding parameters. We found that petrels were exposed to a wide range of pollutants (33 out of 55 showed measurable levels) with PCBs dominating the blood contaminant profiles in both years. Only 9 compounds were detected in >50 % of the birds. Specifically, among OCPs, p, p'-DDE and hexaclorobenzene were the most frequently detected while fluorene and acenaphthene were the most common PAH. The concentrations of ∑5PCBs and ∑7POPs were higher in older birds. Furthermore, females with greater contaminant burdens laid eggs with a lower probability of hatching. However, female investment in egg production (size and volume) was unrelated to their blood contaminant load. Overall, this study highlights the presence of a wide range of contaminants in the petrel's food web, and it sheds light on the potential impact of chronic exposure to sub-lethal levels of PCBs on the breeding success of seabirds. We claim that toxicological testing should be a practice integrated in the management of seabirds, particularly of endangered species to monitor how past and present anthropogenic activities impact their conservation status.

Inter-colony variation in predation, mercury burden and adult survival in a declining seabird

Migratory species with disjunct and localized breeding distributions, including many colonial marine birds, pose challenges for management and conservation as their dynamics are shaped by both broad oceanographic changes and specific factors affecting individual breeding colonies. We compare six colonies of the declining Leach's storm-petrel, Hydrobates leucorhous, across their core range in Atlantic Canada using standard capture-mark-recapture methods to estimate annual survival of individually marked populations of breeding adults. Over the period analysed (5-20 years per colony; 2003-2022), mean annual survival varied among colonies (0.81-0.88) and annually (process error σ ranging from 0.01 to 0.09), though annual fluctuations were not synchronous across colonies. Two colonies with limited natural predation showed higher survival, and there was a decline in survival with increasing colony-specific total mercury burden. Our work shows that colony-specific pressures and regional contaminant burdens are potentially important contributors to current population declines, and highlights the importance of monitoring demographic rates at multiple sites for species that congregate at key life-history stages.

Factors influencing mercury levels in Leach's storm-petrels at northwest Atlantic colonies

Mercury (Hg) is a globally distributed heavy metal, with negative effects on wildlife. Its most toxic form, methylmercury (MeHg), predominates in aquatic systems. Levels of MeHg in marine predators can vary widely among individuals and populations. Leach's storm-petrels (Hydrobates leucorhous) have elevated levels of Hg but the role of Hg in storm-petrel population declines is unknown. In this study, we used egg and blood samples to study variation in Hg exposure among several northwest Atlantic colonies during breeding seasons, thereby evaluating relative toxicity risk within and among colonies. Total mercury (THg) concentrations were higher with increasing colony latitude, and were more pronounced in blood than in eggs. THg concentrations in blood were mostly associated with low toxicity risk in birds from the southern colonies and moderate risks in birds from the northern colonies; however, those values did not affect hatching or fledging success. THg concentrations in both eggs and blood were positively correlated with δ³⁴S, emphasizing the role of sulfate-reducing bacteria in methylation of THg acquired through marine food webs, which is consistent with enriched δ³⁴S profiles. By associating tracking data from foraging trips with THg from blood, we determined that blood THg levels were higher when storm-petrel's intensive search locations were over deeper waters. We conclude that spatial variation in THg concentrations in Leach's storm-petrels is attributable to differences in ocean depth at foraging locations, both at individual and colony levels. Differences in diet among colonies observed previously are the most likely cause for observed blood THg differences. As one of the few pelagic seabird species breeding in Atlantic Canada, with limited overlap in core foraging areas among colonies, Leach's storm-petrels can be used as biomonitors for less sampled offshore pelagic regions. The global trend in Hg emissions combined with legacy levels warrant continued monitoring for toxicity effects in seabirds.

Female and male Leach's Storm Petrels (Hydrobates leucorhous) pursue different foraging strategies during the incubation period

Reproduction in procellariiform birds is characterized by a single egg clutch, slow development, a long breeding season and obligate biparental care. Female Leach's Storm Petrels Hydrobates leucorhous, nearly monomorphic members of this order, produce eggs that are between 20 and 25% of adult body weight. We tested whether female foraging behaviour differs from male foraging behaviour during the ~ 44-day incubation period across seven breeding colonies in the Northwest Atlantic. Over six breeding seasons, we used a combination of Global Positioning System and Global Location Sensor devices to measure characteristics of individual foraging trips during the incubation period. Females travelled significantly greater distances and went farther from the breeding colony than did males on individual foraging trips. For both sexes, the longer the foraging trip, the greater the distance. Independent of trip duration, females travelled farther, and spent a greater proportion of their foraging trips prospecting widely as defined by behavioural categories derived from a Hidden Markov Model. For both sexes, trip duration decreased with date. Sex differences in these foraging metrics were apparently not a consequence of morphological differences or spatial segregation. Our data are consistent with the idea that female foraging strategies differed from male foraging strategies during incubation in ways that would be expected if females were still compensating for egg formation.

Climate oscillations drive millennial-scale changes in seabird colony size

Seabird population size is intimately linked to the physical, chemical, and biological processes of the oceans. Yet, the overall effects of long-term changes in ocean dynamics on seabird colonies are difficult to quantify. Here, we used dated lake sediments to reconstruct ~10,000-years of seabird dynamics in the Northwest Atlantic to determine the influences of Holocene-scale climatic oscillations on colony size. On Baccalieu Island (Newfoundland and Labrador, Canada)-where the world's largest colony of Leach's storm-petrel (Hydrobates leucorhous Vieillot 1818) currently breeds-our data track seabird colony growth in response to warming during the Holocene Thermal Maximum (ca. 9000 to 6000 BP). From ca. 5200 BP to the onset of the Little Ice Age (ca. 550 BP), changes in colony size were correlated to variations in the North Atlantic Oscillation (NAO). By contrasting the seabird trends from Baccalieu Island to millennial-scale changes of storm-petrel populations from Grand Colombier Island (an island in the Northwest Atlantic that is subjected a to different ocean climate), we infer that changes in NAO influenced the ocean circulation, which translated into, among many things, changes in pycnocline depth across the Northwest Atlantic basin where the storm-petrels feed. We hypothesize that the depth of the pycnocline is likely a strong bottom-up control on surface-feeding storm-petrels through its influence on prey accessibility. Since the Little Ice Age (LIA), the effects of ocean dynamics on seabird colony size have been altered by anthropogenic impacts. Subsequently, the colony on Baccalieu Island grew at an unprecedented rate to become the world's largest resulting from favorable conditions linked to climate warming, increased vegetation (thereby nesting habitat), and attraction of recruits from other colonies that are now in decline. We show that although ocean dynamics were an important driver of seabird colony dynamics, its recent influence has been modified by human interference.

Influence of offshore oil and gas structures on seascape ecological connectivity

Offshore platforms, subsea pipelines, wells and related fixed structures supporting the oil and gas (O&G) industry are prevalent in oceans across the globe, with many approaching the end of their operational life and requiring decommissioning. Although structures can possess high ecological diversity and productivity, information on how they interact with broader ecological processes remains unclear. Here, we review the current state of knowledge on the role of O&G infrastructure in maintaining, altering or enhancing ecological connectivity with natural marine habitats. There is a paucity of studies on the subject with only 33 papers specifically targeting connectivity and O&G structures, although other studies provide important related information. Evidence for O&G structures facilitating vertical and horizontal seascape connectivity exists for larvae and mobile adult invertebrates, fish and megafauna; including threatened and commercially important species. The degree to which these structures represent a beneficial or detrimental net impact remains unclear, is complex and ultimately needs more research to determine the extent to which natural connectivity networks are conserved, enhanced or disrupted. We discuss the potential impacts of different decommissioning approaches on seascape connectivity and identify, through expert elicitation, critical knowledge gaps that, if addressed, may further inform decision making for the life cycle of O&G infrastructure, with relevance for other industries (e.g. renewables). The most highly ranked critical knowledge gap was a need to understand how O&G structures modify and influence the movement patterns of mobile species and dispersal stages of sessile marine species. Understanding how different decommissioning options affect species survival and movement was also highly ranked, as was understanding the extent to which O&G structures contribute to extending species distributions by providing rest stops, foraging habitat, and stepping stones. These questions could be addressed with further dedicated studies of animal movement in relation to structures using telemetry, molecular techniques and movement models. Our review and these priority questions provide a roadmap for advancing research needed to support evidence-based decision making for decommissioning O&G infrastructure.

Year-round at-sea movements of fairy prions from southeastern Australia

Effective conservation assessments require detailed information of species' ecological niches during the whole annual cycle. For seabirds, this implies investigating the at-sea distribution and foraging behaviour during both the breeding and non-breeding periods. However, until recently, collecting information about small species has been precluded by the excessive size of the required devices. This lack of knowledge is exacerbated in the case of polytypic genera with species sharing very similar appearance and behaviour, such as the super-abundant prions (Pachyptila spp.). The present study investigates the year-round at-sea distribution and foraging ecology of the fairy prion (Pachyptila turtur) in southeastern Australia. Miniaturized GPS loggers during the breeding season and geolocators (GLS) during the non-breeding period were used over 4 consecutive years (2017-2021), with results that highlight the importance of the continental shelf-edge waters for fairy prions throughout the year. In addition, contrary to previous assumptions, the GLS data revealed an unsuspected post-breeding migration to the waters south of Australia, during which individuals probably undergo a rapid moult of flight feathers. Understanding the at-sea distribution and ecology of prions during the whole annual cycle will be fundamental to their conservation as it can reveal species- or population-specific threats that have been overlooked because of their status as abundant species.

Predicting Source Populations of Vagrants Using Breeding Population Data: A Case Study of the Lesser Black-Backed Gull (Larus fuscus)

Vagrancy is critical in facilitating range expansion and colonization through exploration and occupation of potentially suitable habitat. Uncovering origins of vagrants will help us better understand not only species-specific vagrant movements, but how the dynamics of a naturally growing population influence vagrancy, and potentially lead to range expansion. Under the premise that occurrence of vagrants is linked to increasing population growth in the core of the breeding range, we assessed the utility of breeding population survey data to predict source populations of vagrants. Lesser Black-backed Gulls (LBBG) (Larus fuscus) served as our focal species due to their dramatic and well-documented history of vagrancy to North America in the last 30 years. We related annual occurrence of vagrants to indices of breeding population size and growth rate of breeding populations. We propose that the fastest growing population is the most likely source of recent vagrants to North America. Our study shows that it is possible to predict potential source populations of vagrants with breeding population data, but breeding surveys require increased standardization across years to improve models. For the Lesser Black-backed Gull, Iceland’s breeding population likely influenced vagrancy during the early years of colonization, but the major increase in vagrants occurred during a period of growth of Greenland’s population, suggesting that Greenland is the source population of the most recent pulse of vagrant LBBG to North America.

Marine pollution in fledged Leach's storm-petrels (Hydrobates leucorhous) from Baccalieu Island, Newfoundland and Labrador, Canada

The Leach's storm-petrel (Hydrobates leucorhous) is one of the most abundant and widely distributed marine birds in the North Atlantic but is under global population decline, possibly linked to marine pollution. We determined levels of ingested plastic and hepatic total mercury (THg) in recently fledged juveniles that stranded in Newfoundland and Labrador, Canada, and assessed the relationship to body condition, size and diet. Plastic prevalence was high (87.5%) but hepatic THg was relatively low (mean 486.7 ng/g dry weight) compared to other studies. Levels of neither pollutant were significantly related to body metrics of health. Our data confirm that plastic and mercury are pervasive in the western North Atlantic Ocean, prominent even in young birds.

Temporal and spatial differences in the post-breeding behaviour of a ubiquitous Southern Hemisphere seabird, the common diving petrel

The non-breeding period plays a major role in seabird survival and population dynamics. However, our understanding of the migratory behaviour, moulting and feeding strategies of non-breeding seabirds is still very limited, especially for small-sized species. The present study investigated the post-breeding behaviour of three distant populations (Kerguelen Archipelago, southeastern Australia, New Zealand) of the common diving petrel (CDP) (Pelecanoides urinatrix), an abundant, widely distributed zooplanktivorous seabird breeding throughout the southern Atlantic, Indian and Pacific oceans. The timing, geographical destination and activity pattern of birds were quantified through geolocator deployments during the post-breeding migration, while moult pattern of body feathers was investigated using stable isotope analysis. Despite the high energetic cost of flapping flight, all the individuals quickly travelled long distances (greater than approx. 2500 km) after the end of the breeding season, targeting oceanic frontal systems. The three populations, however, clearly diverged spatially (migration pathways and destinations), and temporally (timing and duration) in their post-breeding movements, as well as in their period of moult. Philopatry to distantly separated breeding grounds, different breeding phenologies and distinct post-breeding destinations suggest that the CDP populations have a high potential for isolation, and hence, speciation. These results contribute to improving knowledge of ecological divergence and evolution between populations, and inform the challenges of conserving migratory species.

Behavioral and trophic segregations help the Tahiti petrel to cope with the abundance of wedge-tailed shearwater when foraging in oligotrophic tropical waters

Two species breeding in sympatry are more likely to coexist if their ecological niches are segregated either in time, space or in trophic habits. Here, we combined GPS-tracking, stable isotope analysis and DNA metabarcoding analysis to understand how the rare Tahiti petrel Pseudobulweria rostrata (TP) copes with the very abundant (i.e. 500,000 breeding pairs) wedge-tailed shearwater Ardenna pacifica (WTS) when breeding in sympatry in a tropical area. WTS foraged in restricted areas along their path, while TP predominantly foraged using extensive search behavior, suggesting a more opportunistic foraging strategy. Interspecific overlap of foraging areas was higher than intraspecific overlap. Breeding seasons largely overlap between species during the study, but TP seems to be asynchronous breeders. TP fed upon prey with higher δ15N values than WTS, and their diet was mainly composed of deep-sea organisms. TP could feed upon dead prey floating at the surface while WTS preyed mainly upon fish species that generally move in schools. Our study highlights several segregating mechanisms (temporal, behavioral and trophic) that could facilitate the coexistence of the two species despite the predominant number of WTS, and provides the very first information on the foraging and trophic ecology of the poorly-known TP.

Citizen science for predicting spatio-temporal patterns in seabird abundance during migration

Pelagic seabirds are elusive species which are difficult to observe, thus determining their spatial distribution during the migration period is a difficult task. Here we undertook the first long-term study on the distribution of migrating shearwaters from data gathered within the framework of citizen science projects. Specifically, we collected daily abundance (only abundance given presence) of Balearic shearwaters from 2005 to 2017 from the online databases Trektellen and eBird. We applied machine-learning techniques, specifically Random Forest regression models, to predict shearwater abundance during migration using 15 environmental predictors. We built separated models for pre-breeding and post-breeding migration. When evaluated for the total data sample, the models explained more than 52% of the variation in shearwater abundance. The models also showed good ability to predict shearwater distributions for both migration periods (correlation between observed and predicted abundance was about 70%). However, relative variable importance and variation among the models built with different training data subsamples differed between migration periods. Our results showed that data gathered in citizen science initiatives together with recently available high-resolution satellite imagery, can be successfully applied to describe the migratory spatio-temporal patterns of seabird species accurately. We show that a predictive modelling approach may offer a powerful and cost-effective tool for the long-term monitoring of the migratory patterns in sensitive marine species, as well as to identify at sea areas relevant for their protection. Modelling approaches can also be essential tools to detect the impacts of climate and other global changes in this and other species within the range of the training data.

Thinking small: Next-generation sensor networks close the size gap in vertebrate biologging

Recent advances in animal tracking technology have ushered in a new era in biologging. However, the considerable size of many sophisticated biologging devices restricts their application to larger animals, whereas older techniques often still represent the state-of-the-art for studying small vertebrates. In industrial applications, low-power wireless sensor networks (WSNs) fulfill requirements similar to those needed to monitor animal behavior at high resolution and at low tag mass. We developed a wireless biologging network (WBN), which enables simultaneous direct proximity sensing, high-resolution tracking, and long-range remote data download at tag masses of 1 to 2 g. Deployments to study wild bats created social networks and flight trajectories of unprecedented quality. Our developments highlight the vast capabilities of WBNs and their potential to close an important gap in biologging: fully automated tracking and proximity sensing of small animals, even in closed habitats, at high spatial and temporal resolution.

Divergence between genes but limited allelic polymorphism in two MHC class II A genes in Leach's storm-petrels Oceanodroma leucorhoa

The major histocompatibility complex (MHC) is critical to host-pathogen interactions. Class II MHC is a heterodimer, with α and β subunits encoded by different genes. The peptide-binding groove is formed by the first domain of both subunits (α₁ and β₁), but studies of class II variation or natural selection focus primarily on the β subunit and II B genes. We explored MHC II A in Leach's storm-petrel, a seabird with two expressed, polymorphic II B genes. We found two II A genes, Ocle-DAA and Ocle-DBA, in contrast to the single II A gene in chicken and duck. In exon 2 which encodes the α₁ domain, the storm-petrel II A genes differed strongly from each other but showed little within-gene polymorphism in 30 individuals: just one Ocle-DAA allele, and three Ocle-DBA alleles differing from each other by single non-synonymous substitutions. In a comparable sample, the two II B genes had nine markedly diverged alleles each. Differences between the α₁ domains of Ocle-DAA and Ocle-DBA showed signatures of positive selection, but mainly at non-peptide-binding site (PBS) positions. In contrast, positive selection within and between the II B genes corresponded to putative PBS codons. Phylogenetic analysis of the conserved α₂ domain did not reveal deep or well-supported lineages of II A genes in birds, in contrast to the pronounced differentiation of DQA, DPA, and DRA isotypes in mammals. This uncertain homology complicates efforts to compare levels of functional variation and modes of evolution of II A genes across taxa.

Comparing imaging, acoustics, and radar to monitor Leach's storm-petrel colonies

Seabirds are integral components of marine ecosystems and, with many populations globally threatened, there is a critical need for effective and scalable seabird monitoring strategies. Many seabird species nest in burrows, which can make traditional monitoring methods costly, infeasible, or damaging to nesting habitats. Traditional burrow occupancy surveys, where possible, can occur infrequently and therefore lead to an incomplete understanding of population trends. For example, in Oregon, during the last three decades there have been large changes in the abundance of Leach’s storm-petrels (Hydrobates leucorhoa), which included drastic declines at some colonies. Unfortunately, traditional monitoring failed to capture the timing and magnitude of change, limiting managers’ ability to determine causes of the decline and curtailing management options. New, easily repeatable methods of quantifying relative abundance are needed. For this study, we tested three methods of remote monitoring: passive acoustic monitoring, time-lapse cameras, and radar. Abundance indices derived from acoustics and imagery: call rates, acoustic energy, and counts were significantly related to traditional estimates of burrow occupancy of Leach’s storm-petrels. Due to sampling limitations, we were unable to compare radar to burrow occupancy. Image counts were significantly correlated with all other indices, including radar, while indices derived from acoustics and radar were not correlated. Acoustic data likely reflect different aspects of the population and hold the potential for the further development of indices to disentangle phenology, attendance of breeding birds, and reproductive success. We found that image counts are comparable with standard methods (e.g., radar) in producing annual abundance indices. We recommend that managers consider a sampling scheme that incorporates both acoustics and imaging, but for sites inaccessible to humans, radar remains the sole option. Implementation of acoustic and camera based monitoring programs will provide much needed information for a vulnerable group of seabirds.