Puffinus Mauretanicus Research Articles

Trophic guilds and niche segregation among marine megafauna in the Bay of Biscay

The structure and functioning of ecosystems are largely determined by the interactions between species within a biological community. Among these interactions, species exhibiting similar vertical and spatial prey preferences can be identified, thereby belonging to the same trophic guild. Our study explored some trophic characteristics of a diverse megafaunal community (cetaceans, tunas, seabirds) in the Bay of Biscay (BoB). Using stable isotope analysis (SIA), we explored the dietary habits and niche overlap among predators. The degree of isotopic niche overlap was generally low, but with certain species exhibiting large and narrow isotopic niche areas (long-finned pilot whales and Balearic shearwaters, respectively). Our results revealed a diversity of dietary preferences leading to the identification of three distinct trophic guilds based on prey functional groups and spatial preferences: cephalopod feeders (e.g. long-finned pilot whales, Cuvier's beaked whales, striped dolphins), crustacean feeders (e.g. fin whales, albacores), and piscivores (e.g. common dolphins, harbour porpoises, bottlenose dolphins, Atlantic bluefin tunas, Balearic shearwaters). Our findings showed resource partitioning and niche differentiation among the megafaunal community, highlighting the complexity of BoB's marine ecosystem. The insights derived from this study hold important implications for ecosystem management and the implementation of conservation initiatives.

The Catalan initiative for the Earth BioGenome Project: contributing local data to global biodiversity genomics.

The Catalan Initiative for the Earth BioGenome Project (CBP) is an EBP-affiliated project network aimed at sequencing the genome of the >40 000 eukaryotic species estimated to live in the Catalan-speaking territories (Catalan Linguistic Area, CLA). These territories represent a biodiversity hotspot. While covering less than 1% of Europe, they are home to about one fourth of all known European eukaryotic species. These include a high proportion of endemisms, many of which are threatened. This trend is likely to get worse as the effects of global change are expected to be particularly severe across the Mediterranean Basin, particularly in freshwater ecosystems and mountain areas. Following the EBP model, the CBP is a networked organization that has been able to engage many scientific and non-scientific partners. In the pilot phase, the genomes of 52 species are being sequenced. As a case study in biodiversity conservation, we highlight the genome of the Balearic shearwater Puffinus mauretanicus, sequenced under the CBP umbrella.

Demographic approaches for assessing the conservation status of Scopoli’s Shearwater Calonectris diomedea and the Balearic Shearwater Puffinus mauretanicus

In the north-western Mediterranean there are two breeding species of procellariforms from the Procellariidae family: Scopoli’s shearwater Calonectris diomedea and the Balearic shearwater Puffinus mauretanicus. Long-term monitoring carried out in a number of breeding colonies provides enough data to be able to assess the conservation status of both species using demographic approaches that estimate parameters such as survival, recruitment and fertility. This type of approach is recommended because it provides a reliable conservation diagnosis and knowledge of the processes that determine variations in population dynamics. Both species were found to have critically low adult survival rates, unexpected in such long-lived species, which makes these populations unviable under current conditions. This agrees with previous available information on incidental bycatch on fishing gears, and confirms that this threat, together with predation by terrestrial carnivores are of critical concern for the conservation of the populations. The fact that some of the breeding colonies did not show a declining trend indicates that several compensatory mechanisms, such as an immigration rescue effect, may be acting at local level. Nevertheless, all the evidence gathered to date suggests that these compensatory mechanisms are not permanent and that if no action is taken these populations could become extinct. In the case of Scopolis’ shearwater, the global population is much more abundant, so there may be time for mitigation actions to be undertaken. Given the size of the breeding population of Balearic shearwaters, we recommend urgent measures be carried out to reduce adult mortality in this endemic species to prevent its extinction.

Climate change drives migratory range shift via individual plasticity in shearwaters

How individual animals respond to climate change is key to whether populations will persist or go extinct. Yet, few studies investigate how changes in individual behavior underpin these population-level phenomena. Shifts in the distributions of migratory animals can occur through adaptation in migratory behaviors, but there is little understanding of how selection and plasticity contribute to population range shift. Here, we use long-term geolocator tracking of Balearic shearwaters (Puffinus mauretanicus) to investigate how year-to-year changes in individual birds' migrations underpin a range shift in the post-breeding migration. We demonstrate a northward shift in the post-breeding range and show that this is brought about by individual plasticity in migratory destination, with individuals migrating further north in response to changes in sea-surface temperature. Furthermore, we find that when individuals migrate further, they return faster, perhaps minimizing delays in return to the breeding area. Birds apparently judge the increased distance that they will need to migrate via memory of the migration route, suggesting that spatial cognitive mechanisms may contribute to this plasticity and the resulting range shift. Our study exemplifies the role that individual behavior plays in populations' responses to environmental change and highlights some of the behavioral mechanisms that might be key to understanding and predicting species persistence in response to climate change.

Correlation between seabirds and fisheries varies by species at fine-scale pattern

Abstract Understanding how fisheries influence seabird distribution is critical in the development of sustainable fisheries management. Species distribution models were applied to analyse the influence of the fishing footprint, discards, and oceanographic factors on seabird attendance patterns to trawlers in the Gulf of Cádiz. More than 30 species of seabirds were attracted to trawlers, although only seven were registered with relatively high frequency and abundance. For these species, fishery footprint was a good predictor for the distribution of four out of seven (yellow-legged gull, lesser black-backed gull, northern gannet, and Cory's shearwater). Yellow-legged and lesser black-backed gull flocked in large numbers to trawlers, mostly in shallow areas where they were also attracted by purse seines. Northern gannets and Cory's shearwaters appeared with relatively high frequency and their distributions correlated with trawler effort and abundance of potential prey discards. Balearic shearwaters were attracted in low numbers and concentrated in shallow areas, where potential prey discards were also more abundant. For these three species, discards as surrogate of natural prey distribution were good predictors of trawler attendance. Our research revealed that, at a local scale, the degree of interaction of seabirds on fishing discards varies by species. Therefore, fine-scale studies are essential in identifying interactions between seabirds and fisheries, and thus assessing conservation issues such as bycatch or the consequences of discard bans.

Do Seabirds Control Wind Drift during Their Migration across the Strait of Gibraltar? A Study Using Remote Tracking by Radar

This study presents data on the directional flying behaviour of the five most abundant seabird species migrating across the Strait of Gibraltar in relation to the wind, as observed from the north coast, based on radar tracking, and identified to species level by visual observations. A total of 318 seabird trajectories were analysed, illustrating the expected east–west or west–east movements in spring and autumn. We hypothesised that the seabirds that cross the Strait channel during their migrations would behave differently with respect to compensation for wind direction, depending on their flight styles, the migratory period, and the prevailing winds. In this regard, our results showed that flapping birds (Razorbill, Puffin, Northern Gannet, and Balearic shearwater) compensated for wind drift independently of the season and the predominant wind direction. This agrees with the theory that suggests that under moderate winds and whenever visual contact with the coastline is present (as in the case of our study), migrants should compensate for wind drift to avoid being drifted towards the coast, off their main direction of flight. However, Cory’s shearwater, an active gliding seabird with long, slender wings, showed an adaptive directional response to wind, allowing it to be drifted in spring when westerly tailwinds were prevalent, but compensated for wind in autumn, when both easterly and westerly winds were similarly frequent. This adaptive flight behaviour allows it to take advantage of the prevailing tailwinds in spring, gaining ground speed and saving energy during its passage through the Strait, while in autumn, more frequent headwind conditions and a more directional migration to the south may favour compensating for wind drift. Our results support the usefulness of bird radar as a remote tool for describing the pattern of animal movements in the marine environment, as well as their behavioural response to atmospheric conditions. These studies are particularly relevant in the current framework of climate change.

The First Genome of the Balearic Shearwater (Puffinus mauretanicus) Provides a Valuable Resource for Conservation Genomics and Sheds Light on Adaptation to a Pelagic lifestyle.

The Balearic shearwater (Puffinus mauretanicus) is the most threatened seabird in Europe and a member of the most speciose group of pelagic seabirds, the order Procellariiformes, which exhibit extreme adaptations to a pelagic lifestyle. The fossil record suggests that human colonisation of the Balearic Islands resulted in a sharp decrease of the Balearic shearwater population size. Currently, populations of the species continue to be decimated mainly due to predation by introduced mammals and bycatch in longline fisheries, with some studies predicting its extinction by 2070. Here, using a combination of short and long reads, we generate the first high-quality reference genome for the Balearic shearwater, with a completeness amongst the highest across available avian species. We used this reference genome to study critical aspects relevant to the conservation status of the species and to gain insights into the adaptation to a pelagic lifestyle of the order Procellariiformes. We detected relatively high levels of genome-wide heterozygosity in the Balearic shearwater despite its reduced population size. However, the reconstruction of its historical demography uncovered an abrupt population decline potentially linked to a reduction of the neritic zone during the Penultimate Glacial Period (∼194–135 ka). Comparative genomics analyses uncover a set of candidate genes that may have played an important role into the adaptation to a pelagic lifestyle of Procellariiformes, including those for the enhancement of fishing capabilities, night vision, and the development of natriuresis. The reference genome obtained will be the crucial in the future development of genetic tools in conservation efforts for this Critically Endangered species.

Balearic shearwater and northern gannet bycatch risk assessment in Portuguese Continental Waters

Even though incidental captures in fisheries are one of the major threats to seabirds, bycatch has been difficult to quantify and specific risk areas are rarely identified. The present study evaluates the potential fisheries bycatch effect on two of the most emblematic seabird species wintering off continental Portugal, the critically endangered Balearic Shearwater and Northern Gannet. Information was collected by on-board observers and voluntary logbooks kept by fishing boat captains. Each species' Potential Biological Removal (for the study area) was based on the respective population abundance estimated through aerial surveys. The analysis of bycatch mortality identified the Fixed Gear in the Polyvalent fleet and Purse Seiners as the fisheries with the highest Balearic Shearwater bycatch rate. Longline and Fixed Gear fisheries had the highest Northern Gannet bycatch rate. The Potential Biological Removal thresholds were 41 Balearic Shearwaters per year (CI = 20–83) and 2345 Northern Gannets per year (CI = 2049–2680). The overlap between the predictive species distribution maps and fisheries density maps allowed for a seabird Bycatch Risk Assessment. The higher Balearic Shearwater bycatch risk was obtained for Fixed Gear and Purse Seines and the highest Northern Gannet bycatch risk was obtained for Longline and Fixed Gear fisheries. Bycatch mitigation measures should be applied in fisheries presenting the higher bycatch risks. This study identifies the potential areas where Balearic Shearwater and Northern Gannet bycatch is more likely to occur, including some of the already designated Special Protection Areas where management and conservation measures should urgently be applied.

Trophic importance of small pelagic fish to marine predators of the Mediterranean Sea

Small pelagic fish (SPF) species such as European sardine Sardina pilchardus, European anchovy Engraulis encrasicolus, round sardinella Sardinella aurita and European sprat Sprattus sprattus play important ecological roles in the Mediterranean Sea marine ecosystem. However, changes in SPF abundance and biomass have recently been observed in the basin. Therefore, uncovering the trophic importance of SPF to their predators is key to unravelling potential ecological causes and consequences of SPF population changes related to predator dynamics. Here, we reviewed 101 published studies reporting the presence of the SPF species named above in the diet of marine predators inhabiting the Mediterranean Sea. We found that the number of species preying on SPF was highest for teleost fish species, followed by elasmobranchs, seabirds, marine mammals, cephalopods and sea turtles. These predators were both commercial and non-commercial taxa, and vulnerability ranged from medium to very high. From a conservation point of view, most predator species were considered Least Concern by the IUCN, with few exceptions such as the Balearic shearwater Puffinus mauretanicus, a Critically Endangered species. Geographic information showed that the European sardine was more important in the diet of predators from the western Mediterranean basin, while European anchovy consumption was higher on the eastern side. Round sardinella was consumed in high amounts in the Tyrrhenian Sea, and European sprat was anecdotally consumed. The importance of SPF in the diet of Mediterranean predators may indicate bottom-up control of the marine ecosystem; however, limited temporal information precluded the evaluation of temporal changes, highlighting the need to develop new studies in this area.

Seabird distribution is better predicted by abundance of prey than oceanography. A case study in the Gulf of Cadiz (SW, Iberian Peninsula)

AbstractQuantifying factors that influence marine predator distributions is essential to understanding the current and future change in marine biodiversity. Here, we test whether marine predator distribution relates to prey, or is better predicted by other specific habitat features. We examine the correlation between spatial distribution of three seabird species and their prey, as well as environmental proxies (oceanographic characteristics) in the Gulf of Cadiz, NE Atlantic. We modeled the at-sea distribution of Cory's shearwater, Balearic shearwater and Northern gannet, based on: (i) pelagic fish abundance according to acoustic surveys, and (ii) a forecast-model of remotely sensed environmental variables (productivity, sea surface temperature, and salinity). In general, seabird distributions were better predicted by abundance of fish than by environmental variables at the habitat scale. We obtained consistent correlations between seabird presence and the abundance of medium-sized (10–20 cm) sardines, anchovies and Mediterranean horse mackerel, providing information on their preferred prey. Additionally, oceanographic productivity variables moderately contributed to seabird distribution models, with better predictive value for the critically endangered Balearic shearwater and Northern gannet in the summer, whilst the model for Cory's shearwater's produced poorer predictions. Predator–prey combined studies may represent essential tools for an efficient ecosystem-based management of marine environments.

Machine learning as a successful approach for predicting complex spatio–temporal patterns in animal species abundance

Our aim was to identify an optimal analytical approach for accurately predicting complex spatio–temporal patterns in animal species distribution. We compared the performance of eight modelling techniques (generalized additive models, regression trees, bagged CART, k–nearest neighbors, stochastic gradient boosting, support vector machines, neural network, and random forest –enhanced form of bootstrap. We also performed extreme gradient boosting –an enhanced form of radiant boosting– to predict spatial patterns in abundance of migrating Balearic shearwaters based on data gathered within eBird. Derived from open–source datasets, proxies of frontal systems and ocean productivity domains that have been previously used to characterize the oceanographic habitats of seabirds were quantified, and then used as predictors in the models. The random forest model showed the best performance according to the parameters assessed (RMSE value and R2). The correlation between observed and predicted abundance with this model was also considerably high. This study shows that the combination of machine learning techniques and massive data provided by open data sources is a useful approach for identifying the long–term spatial–temporal distribution of species at regional spatial scales.

First days at sea: depicting migration patterns of juvenile seabirds in highly impacted seascapes.

Increasing human activities have detrimental consequences on marine ecosystems and their impact can have cumulative effects. Within marine ecosystems, seabirds respond to ecosystem variability and face multiple human pressures, especially threatened species. In long-lived species, juveniles and immatures could represent up to 50% of the total population, but their migratory movements remain largely unknown. Here, we depict the migratory patterns of juvenile Balearic shearwaters Puffinus mauretanicus, the most threatened European seabird, using miniaturised satellite transmitters. At the end of the 2012 breeding season, five tagged juveniles left the breeding colonies of Eivissa Island (western Mediterranean) the first week of July. They moved westwards to reach the Atlantic Ocean between 3 and 13 days afterwards. Juveniles showed a two-phase migratory pattern: they first travelled slower close to the breeding colonies, and then moved towards their wintering areas in the Atlantic Ocean by rapid directional movements. Environmental cues (e.g.,marine productivity, water mass distribution, frontal systems) might have a prominent role in driving the migratory patterns of juvenile Balearic shearwaters, moving from warm and poor marine areas in the Mediterranean Sea to cooler and rich non-breeding grounds in the Atlantic Ocean. Based on observational findings, we observed certain spatial overlap of juvenile Balearic shearwaters with areas of high human impact, but the relationship between flying travel speed and both fishing effort and cumulative human impacts were not statistically significant. These results suggest that more research is needed to assess whether the movement patterns of migrating juveniles are affected by human activities. Therefore, understanding the at-sea spatial ecology of juveniles should be a priority for research and conservation due to the importance of this population component in long-lived species, as well as assessing their vulnerability to multiple anthropogenic pressures.

Drivers for spatial modelling of a critically endangered seabird on a dynamic ocean area: Balearic shearwaters are non‐vegetarian

AbstractSpatial modelling is an important research tool to improve our knowledge about the distribution of wildlife in the ocean. Using different modelling techniques (MaxEnt and a generalized linear mixed model), a predictive habitat suitability model was developed for one of the most threatened seabirds in the world: the Balearic shearwater,Puffinus mauretanicus.Models were developed using a 10‐year dataset from the Gulf of Cádiz (on the south‐western Iberian Peninsula), a key foraging area for Balearic shearwaters during migration and the non‐breeding season.Predictive habitat maps strongly matched the observed distribution patterns, pointing to bathymetric features as the main modelling drivers. The species was concentrated on shallow areas (up to approximately 100 m in depth) of the continental shelf, very close to the mouth of the Guadalquivir River. In contrast with previous studies, Balearic shearwater distribution in the highly dynamic Gulf of Cádiz was not correlated with areas of high chlorophyllaconcentration.This lack of spatial correlation probably arises from the delay between the phytoplankton bloom and the response of the zooplankton and small fish that are preyed upon by Balearic shearwaters, which may result in important displacements of this trophic chain across the Gulf of Cádiz.The analysis presented contributes to a better understanding of the spatial distribution and ecology of the critically endangered top predator in the Gulf of Cádiz and offers important information to improve management plans.

Where to head: environmental conditions shape foraging destinations in a critically endangered seabird

Foraging distribution of flying seabirds is constrained by environmental factors influencing individual decision-making. This must be particularly true during the breeding period, when individuals face additional limitations imposed by their central-place foraging behaviour. We used GPS data loggers and Argos PTTs to track the foraging flights of Balearic shearwaters (Puffinus mauretanicus) during the chick-rearing period of 2011–2014 in the Balearic Islands (Western Mediterranean). We identified main areas used by tracked birds and characterised their productivity patterns. Based on a spatial seascape approach of flight costs varying with time, shaped by environmental processes as winds, we also estimated flight costs to reach foraging grounds in outward and return trips from the colony. Individuals repeatedly used the closest areas on the Iberian continental shelf. However, sporadic and favourable wind conditions facilitated low-cost flight to more distant and equally productive areas of the western North African shelf.

Consistent concentrations of critically endangered Balearic shearwaters in UK waters revealed by at-sea surveys.

AimEurope's only globally critically endangered seabird, the Balearic shearwater (Puffinus mauretanicus), is thought to have expanded its postbreeding range northwards into UK waters, though its at sea distribution there is not yet well understood. This study aims to identify environmental factors associated with the species’ presence, map the probability of presence of the species across the western English Channel and southern Celtic Sea, and estimate the number of individuals in this area.LocationThe western English Channel and southern Celtic Sea.MethodsThis study analyses strip transect data collected between 2013 and 2017 from vessel‐based surveys in the western English Channel and southern Celtic Sea during the Balearic shearwater's postbreeding period. Using environmental data collected directly and from remote sensors both Generalized Additive Models and the Random Forest machine learning model were used to determine shearwater presence at different locations. Abundance was estimated separately using a density multiplication approach.ResultsBoth models indicated that oceanographic features were better predictors of shearwater presence than fish abundance. Seafloor aspect, sea surface temperature, depth, salinity, and maximum current speed were the most important predictors. The estimated number of Balearic shearwaters in the prediction area ranged from 652 birds in 2017 to 6,904 birds in 2014.Main conclusionsAreas with consistently high probabilities of shearwater presence were identified at the Celtic Sea front. Our estimates suggest that the study area in southwest Britain supports between 2% and 23% of the global population of Balearic shearwaters. Based on the timing of the surveys (mainly in October), it is probable that most of the sighted shearwaters were immatures. This study provides the most complete understanding of Balearic shearwater distribution in UK waters available to date, information that will help inform any future conservation actions concerning this endangered species.

Mercury Exposure in Birds Linked to Marine Ecosystems in theWestern Mediterranean.

Mercury (Hg), particularly as methylmercury (MeHg), is a nonessential, persistent, and bioaccumulative toxic element with high biomagnification capacity and is considered a threat to marine environments. We evaluated total Hg concentrations in liver, kidney, and brain in 62 individuals of 9 bird species linked to marine ecosystems from western Mediterranean admitted in a Wildlife Rehabilitation Center (WRC) (Alicante, Spain, 2005-2020). Age- and sex-related differences in Hg levels, as well as the cause of admission to the WRC, were alsoevaluated in certain species. The species studied were: northern gannet (Morus bassanus), European shag (Phalacrocorax aristotelis), great cormorant (Phalacrocorax carbo), osprey (Pandion haliaetus), Balearic shearwater (Puffinus mauretanicus), yellow-legged gull (Larus michahellis), razorbill (Alca torda), common tern (Sterna hirundo), and black-headed gull (Chroicocephalus ridibundus). Concentrations in feathers of 27 individuals, and concentrations in internal tissues in 7 other individuals of 7 different species were alsoreported but not statistically evaluated due to the limited number of samples. Results suggest that individuals were chronically exposed to Hg through diet. The differences in Hg concentrations among speciesmay beexplained by theirdiet habits. Mercury concentrations strongly correlated between tissues (r = 0.78-0.94, p < 0.001, n = 61-62). Some individuals of certain species (i.e., European shag, northern gannet, and great cormorant) showed Hg concentrations close to or above those described in the literature as causing reproductive alterations in other avian species. Consequently, certain individuals inhabiting western Mediterranean could be at risk of suffering long-term, Hg-related effects. Some of the species evaluated are listed within different categories of threat according to the International Union forConservation of Nature (IUCN) and are endangered at a national level, so this study will provide valuable information for assessors and authorities in charge of the management of the environment and pollution.

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.

How adequately are the critically endangered Balearic Shearwaters protected by the Special Protection Areas (SPAs) for seabirds? A case study in the Gulf of Cadiz

The expansion of marine protected areas in pelagic areas has been crucial to achieve sufficient protection of the oceans. However, there is still some controversy about whether these protected areas actually cover the vital areas for some species. We investigate the summer distribution of the critically endangered Balearic Shearwater and its overlap with the Special Protection Area for seabirds (SPA), using the Gulf of Cadiz as a case study. This area holds the SPA named Marine Area of Gulf of Cádiz, covering 2314.2 km2. A dataset of nine years of vessel-based surveys between 2006 and 2017 was analysed, using Kernel Density Estimation to generate the core area polygons for each year. The area located off the Bay of Cádiz, southeast of the mouth of the Guadalquivir, has revealed as a very consistent key area for this species during summer. This area, covering 1082 km2, regularly hosted populations that exceeded the threshold for area of international importance (IBA criteria) for the species. The current SPA covers less than 40% of this new key area. The limitation in the number of years of monitoring and seasonal differences in the dataset used to establish the boundaries of the current protected area may be at the base of these discrepancies. This study emphasizes the importance of synthesizing and collecting long-term information to define marine protected areas and to assess their efficiency over the time. Furthermore, our study highlights the urgent need to expand this marine protected area to protect effectively this critically threatened species.

Patterns of at-sea behaviour at a hybrid zone between two threatened seabirds

Patterns of behavioural variation and migratory connectivity are important characteristics of populations, particularly at the edges of species distributions, where processes involved in influencing evolutionary trajectories, such as divergence, mutual persistence, and natural hybridization, can occur. Here, we focused on two closely related seabird species that breed in the Mediterranean: Balearic shearwaters (Puffinus mauretanicus) and Yelkouan shearwaters (Puffinus yelkouan). Genetic and phenotypic evidence of hybridization between the two species on Menorca (the eastern and westernmost island in the breeding ranges of the two shearwaters, respectively) has provided important insights into relationships between these recently diverged species. Nevertheless, levels of behavioural and ecological differentiation amongst these populations remain largely unknown. Using geolocation and stable isotopes, we compared the at-sea movement behaviour of birds from the Menorcan ‘hybrid’ population with the nearest neighbouring populations of Balearic and Yelkouan shearwaters. The Menorcan population displayed a suite of behavioural features intermediate to those seen in the two species (including migration strategies, breeding season movements and limited data on phenology). Our findings provide new evidence to support suggestions that the Menorcan population is admixed, and indicate a role of non-breeding behaviours in the evolutionary trajectories of Puffinus shearwaters in the Mediterranean.

The importance of Portuguese Continental Shelf Waters to Balearic Shearwaters revealed by aerial census

Portuguese Wildlife Society and projects SafeSea EEA-Grants, FAME (Proj. 2009-1/089) and European Commission’s Life Programme (MarPro NAT/PT/00038). This study was also partly supported by the Portuguese Foundation for Science and Technology (FCT) with Grants SFRH/ BD/30240/2006 to M. Ferreira and SFRH/BD/32841/2006 to P. C. Rodrigues. C. Eira is supported by FCT through CESAM UID/AMB/50017/2013 co-funded by FCT/MEC and FEDER, within PT2020 and Compete 2020 and S. Monteiro is financed by a Grant (BPD/0043/AMB/50017) from UID/AMB/50017/2013. This work was also partially supported by the strategic programme UID/BIA/04050/2013 (POCI-01-0145-FEDER-007569) funded by FCT and by ERDF (COMPETE2020). The authors thank observers and airplane pilots who contributed to this work