SUMMARYPelagic birds, which wander in the open sea most of the year and often nest on small remote oceanic islands, are able to pinpoint their breeding colony even within an apparently featureless environment, such as the open ocean. The mechanisms underlying their surprising navigational performance are still unknown. In order to investigate the nature of the cues exploited for oceanic navigation, Cory's shearwaters, Calonectris borealis, nesting in the Azores were displaced and released in open ocean at about 800km from their colony, after being subjected to sensory manipulation. While magnetically disturbed shearwaters showed unaltered navigational performance and behaved similarly to unmanipulated control birds, the shearwaters deprived of their sense of smell were dramatically impaired in orientation and homing. Our data show that seabirds use olfactory cues not only to find their food but also to navigate over vast distances in the ocean. Supplementary material available online at

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The existence of two seasonally distinct breeding populations of Oceanodroma storm-petrels in the Azores islands was first documented in 1996. The discovery of morphological differences between the populations led to the suggestion that they may represent cryptic sibling species. Recent mtDNA and microsatellite analysis from storm-petrel populations has considerably advanced our understanding of their taxonomic relationships. Here we present new information on the timing of breeding and moult of the two Azores populations, the extent of exchange of individuals between seasons, and diet from feather isotopes. We conclude that the hot-season Azores population should be considered a new species for which we propose the name Oceanodroma monteiroi , Monteiro's Storm-petrel. The species is both genetically distinct and genetically isolated from the sympatric cool-season population of Madeiran Storm-petrel Oceanodroma castro , and from all other populations of Oceanodroma castro in the Atlantic and Pacific Oceans examined to date. Differences in the vocalizations permit species recognition, and the extent of primary feather wear and stage of moult aids separation of the two species in the Azores, which is especially valuable during August when both attend the breeding colonies in large numbers. Feather carbon and nitrogen isotopes reveal that the diet of Monteiro's Storm-petrel differs from that of the sympatric Madeiran Storm-petrel during both breeding and non-breeding seasons, and unlike the Madeiran Storm-petrel, Monteiro's Storm-petrel appears to maintain the same foraging environment during the summer and winter months, though it shows a dietary shift to higher trophic levels during the non-breeding season. Monteiro's Storm-petrel is thought to be confined to the Azores archipelago, where it is currently known to nest on just two small neighbouring islets. The total population size was estimated at 250-300 pairs in 1999.

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Although 92% of avian species are socially monogamous, extra‐pair copulation (EPC), resulting in extra‐pair paternity (EPP), is a common reproductive strategy in birds. Among seabirds, in which the rate of social monogamy reaches 100%, Procellariiformes (albatrosses and petrels) show low EPP rates, with the noticeable exception of the only albatross investigated in this regard, the Waved Albatross Phoebastria irrorata. This species, in which forced copulations are known to occur, showed a surprisingly high rate of EPP (25% of chicks). We investigate here EPP rates in another albatross species, the Wandering Albatross Diomedea exulans, subject to a demographic survey conducted for 38 years. We combined data on pair bonds with analysis of ten microsatellite loci and found that 10.7% of 75 chicks had an extra‐pair sire. Although there was some evidence for inbreeding avoidance, within‐pair and extra‐pair chicks showed similar levels of heterozygosity, and the incidence of EPP was independent of age, experience or past reproductive success. Hence, we found no evidence that females benefit from EPCs. Owing to the male‐biased sex ratio in adults, widowed and divorced males required more time to find a new mate (+28 and +72%, respectively) than did females. Combined with high sexual size dimorphism, this phenomenon might promote the forced copulations observed in this species. Our data therefore suggest that EPC is beneficial to unpaired males but occurs at random in females, consistent with the hypothesis that EPP results solely from forced EPCs. However, the importance of the latter for EPP and the part played by solitary males require further investigation.

Environmental variability, costs of reproduction, and heterogeneity in individual quality are three important sources of the temporal and interindividual variations in vital rates of wild populations. Based on an 18-year monitoring of an endangered, recently described, long-lived seabird, Monteiro's Storm-Petrel (Oceanodroma monteiroi), we designed multistate survival models to separate the effects of the reproductive cost (breeders vs. nonbreeders) and individual quality (successful vs. unsuccessful breeders) in relation to temporally variable demographic and oceanographic properties. The analysis revealed a gradient of individual quality from nonbreeders, to unsuccessful breeders, to successful breeders. The survival rates of unsuccessful breeders (0.90 +/- 0.023, mean +/- SE) tended to decrease in years of high average breeding success and were more sensitive to oceanographic variation than those of both (high-quality) successful breeders (0.97 +/- 0.015) and (low-quality) nonbreeders (0.83 +/- 0.028). Overall, our results indicate that reproductive costs act on individuals of intermediate quality and are mediated by environmental harshness.

Trophic ecology and movements are critical issues for understanding the role of marine predators in food webs and for facing the challenges of their conservation. Seabird foraging ecology has been increasingly studied, but small elusive species, such as those forming the 'little shearwater' complex, remain poorly known. We present the first study on the movements and feeding ecology of the Barolo shearwater Puffinus baroli baroli in a colony from the Azores archipelago (NE Atlantic), combining global location-sensing units, stable isotope analyses of feathers (δ 13 C and δ 15 N), stomach flushings and data from maximum depth gauges. During the chick-rearing period, parents visited their nests most nights, foraged mainly south of the colony and fed at lower trophic levels than during the non-breeding period. Squid was the most diverse prey (6 families and at least 10 different taxa), but species composition varied considerably between years. Two squid families, Onychoteuthidae and Argonautidae, and the fish family Phycidae accounted for 82.3% of ingested prey by number. On average, maximum dive depths per foraging trip reached 14.8 m (range: 7.9 to 23.1 m). After the breeding period, birds dispersed offshore in all directions and up to 2500 km from the breeding colony, and fed at higher trophic levels. Overall, our results indicate that the Barolo shearwater is a non-migratory shearwater feeding at the lowest trophic level among Macaronesian seabirds, showing both diurnal and nocturnal activity and feeding deeper in the water column, principally on small schooling squid and fish. These traits contrast with those of 3 other Azorean Procellariiformes (Cory's shearwater Calonectris diomedea, the Madeiran storm-petrel Oceanodroma castro and Monteiro's storm-petrel O. monteiroi), indicating ecological segregation within the Azorean seabird community.

Aim Our current understanding of migratory strategies and the reasons for their high 27 variability along the phylogenetic tree remains relatively poor. Most of the hypotheses 28 relating to migration have been formulated for terrestrial taxa; classically, oceanic migrations 29 were considered as merely dispersive due to the scarcity of observations in the open ocean. 30We describe for the first time, the migration strategy of a small seabird, the Bulwer's petrel 31 (Bulweria bulwerii), and provide new insights into the ecology and evolution of long-distance 32 marine migrations. 33 Location Subtropical and tropical Atlantic Ocean. 34Methods Using cutting-edge geolocators, we examined the year-round distribution and at-sea 35 activity patterns of adult Bulwer's petrels sampled at 5 localities throughout its breeding 36 range in the Atlantic: the Azores, Salvages, Canary and Cape Verde archipelagos. We 37 assessed the migratory connectivity of the species and its habitat use at population and meta-38 population scales. 39Results Our results provide the first evidence of an oriented leapfrog migration in oceanic 40 seabirds. Ecological niche models based on breeding-season data effectively predicted that 41 subtropical waters of the South Atlantic would be the preferred habitat for the northern 42 populations of Bulwer's petrels during the non-breeding season. Habitat modelling also 43 highlighted similarities in distributions between the breeding and non-breeding periods for the 44 southern populations. Data on at-sea activity patterns suggested that birds from the northern 45 and southern populations behave differently during the breeding season, as well as in the 46 northern and southern non-breeding ranges during the non-breeding period. 47Main conclusions These results indicate that specific habitat preferences, presumably related 48 to differences in prey availability, explain the observed distributions and hence the pattern of 49 leapfrog migration described for Bulwer's petrel. Our study demonstrates the utility of 50Page 3 integrating diverse tracking data from multiple populations across international boundaries, 51 and habitat modelling, for identifying important areas common to many marine species in the 52 vast oceanic environments. 53 54 Keywords: Activity patterns, Bulweria bulwerii, Bulwer's petrel, capture-mark-recapture, 55 geolocator data, habitat modelling, Macaronesian seabirds, meta-population studies, oceanic 56 migrations. 57Page 4 INTRODUCTION 58Migration is an integral part of the annual life-cycle and life-history of many animal species. 59