Understanding migration of pelagic seabirds with stable isotopes and geolocation

[eng] Animal migration is an amazing widespread phenomenon that forms an essential component of the animal life history. Animals usually migrate to take advantages of changes in resource availability in space and time or to find suitable habitats for different life-history stages, which ultimately may improve their fitness. Unfortunately, migratory species are currently experiencing substantial population declines because of the several threats they are exposed to. These largely depend on their migratory patterns, and therefore its study is crucial for the effective conservation of migratory species. Despite our wealth of knowledge on avian migration, the study of migratory ecology of pelagic seabirds is still very challenging, especially in small species. Until recently, most studies on seabird migration focused on species of the Southern Ocean, while our knowledge on Mediterranean, tropical and subtropical Atlantic species is scarcer. In this thesis, we aim to fill in this gap of knowledge for a number of pelagic seabirds of the Mediterranean and the Atlantic, by studying the migratory patterns of 7 shearwaters, 4 petrels and 1 gull species. More specifically, we (1) increase our knowledge on different methodologies for seabird identification as a preliminary step to study their migratory movements; (2) evaluate the utility of stable isotopes analysis (SIA) to infer the non-breeding areas of pelagic seabirds, and; (3) reveal the migratory patterns and non-breeding areas of the study species using geolocation or a combination of SIA and geolocation data. Our findings pointed out the importance of integrating different methodologies to distinguish individuals of closely related or recently diverged species and thus overcome their identification difficulty. Furthermore, we demonstrated the utility of SIA as powerful approach to discriminate species that explore isotopically distinct areas. We verified a generally high efficiency of SIA on feathers as a geographic marker to infer the previous non-breeding area of pelagic seabirds. However, SIA efficiency varied at inter-specific level depending on the degree of isotopic differentiation among their non-breeding areas. Based on geolocation and isotopic data, we found a huge variability in migratory patterns among species, population and individuals. At inter-population level, we described for the first time a leap-frog migration pattern in an oceanic seabird, while at intra-population level we revealed the existence of partial migration and other complex migratory patterns. Additionally, we integrated our results and information from literature to review the main extrinsic and intrinsic drivers of migratory patterns of small and medium size seabirds and how they may differ from the ones affecting the migration of terrestrial birds. In opposite to the characteristics of terrestrial habitats, the almost lack of major barriers to migration, the low productivity of tropical waters and the biological adaptations of seabirds to the oceanic habitats seem to contribute to the long-distance migrations and huge variability in migratory patterns of small and medium sized pelagic seabirds. However, this variability is still smaller than the one observed in terrestrial species probably because of the absence of major barriers and the milder climatic seasonality of the oceans. Overall, this thesis gives an important contribution to a wider understanding of the complex migratory ecology of pelagic seabirds.[cat] La migració animal és un fenomen generalitzat increïble que forma un component esencial de la història de la vida animal. Els animals generalment migren per aprofitar els canvas en la disponibilitat espacial i temporal dels recursos, o per trobar un hàbitat adequat per a les diferents etapes del cicle biològic, que en última instància poden millorar la seva condició física o l’èxit reproductiu. Per desgràcia, les espècies migratòries estan actualmente experimentant una disminució substancial en les seves poblacions per causa de les diverses amenaces a què estan exposats. Això depèn en gran mesura de les seves patrons migratoris,i, per tant, el seu estudi és crucial per a la conservació efectiva de les espècies migratòries. Malgrat la nostra riquesa de coneixements sobre la migració aviària, l’estudi de l’ecologia migratòria de les aus marines pelàgiques segueix essent molt difícil, sobretot en les espècies més petites. Fins fa poc, molts dels estudis migratoris de les aus marines s’han centrat en les espècies de les aigües oceàniques de l’hemisferi sud, mentre que el nostra coneixement de les espècies del Mediterrani i de l’Atlàntic tropical i subtropical és més escassa. En aquesta tesi, el nostre objectiu és omplir aquest buit de coneixement per un nombre d’aus marines pelàgiques del Mar Mediterrani i de l’Oceà Atlàntic mitjançant l’estudi dels patrons migratoris de 7 baldrigues, petrells 4 i 1 espècie de gavina. Més específicament, volem (1) utilitzar taxonomia integrada per augmentar el nostre coneixement sobre diferents metodologies per a la identificació d’aus marines, com a pas previ per estudiar els seus moviments migratoris; (2) avaluar la utilitat de l’anàlisi d’isòtops estables (SIA) per inferir les àrees de hivernada d’aus marines pelàgiques; i (3) revelar els patrons migratoris i les àrees de hivernada de les espècie d’estudi utilitzant geolocalització o una combinació de les dades de geolocalització i SIA. Els nostres resultats assenyalen la importància d’integrar diverses metodologies per distinguir individus d’espècies estretament relacionades o que fa poc que van divergir i així superar la dificultat de la seva identificació. D’altra banda, hem demostrat la utilitat del SIA com una metodologia poderosa per discriminar les espècies que exploren àrees isotòpicament distintes. En general, hem verificat una alta eficiència del SIA de les plomes com un marcador geogràfic per inferir les àrees de hivernada de les aus pelàgiques. No obstant això, l’eficiència de SIA va variar a nivell interespecífic en funció del grau de diferenciació isotòpica entre les seves àrees de hivernada. En base a les dades de geolocalització i dels valors isotòpiques de les espècies de estudi, hem trobat una enorme variabilitat de patrons migratoris entre espècies, poblacions i individus. A nivell inter-poblacional, es va descriure per primera vegada un patró de migració salt de granota en una au oceànica, mentre que a nivell intra-poblacional es va revelar l’existència de la migració parcial i altres patrons migratoris molt complexes. A més, hem integrat els nostres resultats i la informació de la literatura per revisar els principals factors extrínsecs i intrínsecs que influencien els patrons migratoris de aus marines petites i mitjanes i com poden diferir de les que afecten la migració de les aus terrestres. Al contrari de les característiques dels hàbitats terrestres, la quasi absència de grans barreres a la migració, la baixa productivitat de les aigües tropicals i les adaptacions biològiques de les aus marines als hàbitats oceànics sembla contribuir a les seves migracions de llarga distància i gran variabilitat en els seus patrons migratoris. No obstant això, aquesta variabilitat és encara menor que l’observada en les espècies terrestres, probablement a causa de l’absència de barreres importants i de l’estacionalitat climàtica més lleu dels oceans. En general, aquesta tesi dóna una important contribució a una millor comprensió de l’ecologia complexa migratòria de les aus marines pelàgiques

Population size, breeding biology and on-land threats of Cape Verde petrel (Pterodroma feae) in Fogo Island, Cape Verde

Cape Verde petrel (Pterodroma feae) is currently considered near threatened, but little is known about its population size, breeding biology and on land threats, jeopardizing its management and conservation. To improve this situation, we captured, marked and recaptured (CMR) birds using mist-nets over 10 years; measured and sexed them; monitored up to 14 burrows, deployed GPS devices on breeders and analyzed activity data of geolocators retrieved from breeders in Fogo (Cape Verde). We set cat traps over the colony and investigated their domestic/feral origin by marking domestic cats from a nearby village with transponders, by deploying GPS devices on domestic cats and by performing stable isotope analyses of fur of the trapped and domestic cats. The population of Fogo was estimated to be 293 birds, including immatures (95% CI: 233-254, CMR modelling). Based on geolocator activity data and nest monitoring we determined the breeding phenology of this species and we found biometric differences between sexes. While monitoring breeding performance, we verified a still ongoing cat predation and human harvesting. Overall, data gathered from trapped cats without transponder, cats GPS trips and the distinct isotopic values between domestic and trapped cats suggest cats visiting the colony are of feral origin. GPS tracks from breeders showed birds left and returned to the colony using the sector NE of the islands, where high level of public lights should be avoided specially during the fledging period. Main threats for the Cape Verde petrel in the remaining breeding islands are currently unknown but likely to be similar to Fogo, calling for an urgent assessment of population trends and the control of main threats in all Cape Verde Islands and uplisting its conservation status

Population size, breeding biology and on-land threats of Cape Verde petrel (Pterodroma feae) in Fogo Island, Cape Verde

Cape Verde petrel (Pterodroma feae) is currently considered near threatened, but little is known about its population size, breeding biology and on land threats, jeopardizing its management and conservation. To improve this situation, we captured, marked and recaptured (CMR) birds using mist-nets over 10 years; measured and sexed them; monitored up to 14 burrows, deployed GPS devices on breeders and analyzed activity data of geolocators retrieved from breeders in Fogo (Cape Verde). We set cat traps over the colony and investigated their domestic/feral origin by marking domestic cats from a nearby village with transponders, by deploying GPS devices on domestic cats and by performing stable isotope analyses of fur of the trapped and domestic cats. The population of Fogo was estimated to be 293 birds, including immatures (95% CI: 233-254, CMR modelling). Based on geolocator activity data and nest monitoring we determined the breeding phenology of this species and we found biometric differences between sexes. While monitoring breeding performance, we verified a still ongoing cat predation and human harvesting. Overall, data gathered from trapped cats without transponder, cats GPS trips and the distinct isotopic values between domestic and trapped cats suggest cats visiting the colony are of feral origin. GPS tracks from breeders showed birds left and returned to the colony using the sector NE of the islands, where high level of public lights should be avoided specially during the fledging period. Main threats for the Cape Verde petrel in the remaining breeding islands are currently unknown but likely to be similar to Fogo, calling for an urgent assessment of population trends and the control of main threats in all Cape Verde Islands and uplisting its conservation status

Spatial scales of marine conservation management for breeding seabirds

Knowing the spatial scales at which effective management can be implemented is fundamental for conservation planning. This is especially important for mobile species, which can be exposed to threats across large areas, but the space use requirements of different species can vary to an extent that might render some management approaches inefficient. Here the space use patterns of seabirds were examined to provide guidance on whether conservation management approaches should be tailored for taxonomic groups with different movement characteristics. Seabird tracking data were synthesised from 5419 adult breeding individuals of 52 species in ten families that were collected in the Atlantic Ocean basin between 1998 and 2017. Two key aspects of spatial distribution were quantified, namely how far seabirds ranged from their colony, and to what extent individuals from the same colony used the same areas at sea. There was evidence for substantial differences in patterns of space-use among the ten studied seabird families, indicating that several alternative conservation management approaches are needed. Several species exhibited large foraging ranges and little aggregation at sea, indicating that area-based conservation solutions would have to be extremely large to adequately protect such species. The results highlight that short-ranging and aggregating species such as cormorants, auks, some penguins, and gulls would benefit from conservation approaches at relatively small spatial scales during their breeding season. However, improved regulation of fisheries, bycatch, pollution and other threats over large spatial scales will be needed for wide-ranging and dispersed species such as albatrosses, petrels, storm petrels and frigatebirds