Sexual segregation in foraging occurs in many animal species, resulting in the partitioning of resources and reduction of competition between males and females, yet the patterns and drivers of such segregation are still poorly understood. We studied the foraging movements (GPS-tracking), habitat use (habitat modelling) and trophic ecology (stable isotope analysis) of female and male Cory’s shearwaters Calonectris borealis during the mid chick-rearing period of six consecutive breeding seasons (2010–2015). We found a clear sexual segregation in foraging in years of greater environmental stochasticity, likely years of lower food availability. When food became scarce, females undertook much longer foraging trips, exploited more homogeneous water masses, had a larger isotopic niche, fed on lower trophic level prey and exhibited a lower body condition, when compared to males. Sexual competition for trophic resources may be stronger when environmental conditions are poor. A greater foraging success of one sex may result in differential body condition of pair mates when enduring parental effort, and ultimately, in an increased probability of breeding failure.

The foraging plasticity in a pelagic seabird species, Cory's shearwater Calonectris diomedea, was compared during incubation and chick-rearing among 7 different breeding sites in the North Atlantic. These sites, with contrasting ecological conditions, were situated in the Azores (Corvo, Faial, Graciosa and Sta. Maria), Berlengas (Berlenga), Madeira (Desertas) and Selvagens (Selvagem Grande) archipelagos. Behavioural data were obtained by intensively deploying compasstemperature and temperature-depth data loggers, monitoring 302 and 22 foraging excursions, respectively. A principal component analysis revealed 2 main groups, one foraging along a neritic shelf (Berlengas population) and the other foraging in pelagic oceanic areas (populations from Azores, Madeira and Selvagens). There was a significant positive correlation (r S = 0.55) between the percentage of short foraging trips in the different breeding sites and the concentration of chlorophyll-a in the waters surrounding those sites. Birds exploiting neritic areas used shallower depths (4.9 ± 2.3 m) and shorter dives (17.0 ± 2.2 s) than birds feeding in oceanic waters (9.8 ± 2.4 m and 32.0 ± 5.8 s respectively). This indicates that birds adapted their modes of predation to cope with the diverse distribution of their prey items. Overall, the behavioural response of the different populations was mainly dictated by the heterogeneity of their habitat, which was driven by 2 productivity gradients present in the north Atlantic. (1) Productivity is expected to increase from the subtropical warmer waters close to Selvagens to northern colder waters north of the Azores archipelago. (2) Oceanic environments are expected to be less profitable than coastal areas (upwelling areas), such as the Portuguese and African coasts. KEY WORDS: Data loggers · Ecological plasticity · Environmental heterogeneity · Foraging behaviour · SeabirdResale or republication not permitted without written consent of the publisher

The conservation of threatened seabirds that are highly pelagic, such as the gadfly petrels Pterodroma spp., depends on understanding the main oceanographic determinants of their movements in order to apply the necessary management regulations and to identify and protect their key marine habitats. The present work presents for the first time information on the distribution and habitat preferences of 17 Bugio petrels Pterodroma deserta from the island of Bugio, Madeira archipelago, North Atlantic Ocean. All of the birds remained in North Atlantic waters during the pre-laying exodus, incubation and chick-rearing periods, showing a clear preference for deep, productive (high chlorophyll a levels) waters north of the Azores archipelago. There was high individual variability in migration strategies. Five wintering areas were identified: two off the Brazilian coast, one around the Cape Verde archipelago, one off the southeast coast of the United States, and one in pelagic waters in the central South Atlantic. These tended to be areas of high productivity but not of a particular sea surface temperature regime. Based on saltwater immersion data, birds were more active during the breeding season and spent more time resting on the water in wintering areas. There was also a positive correlation between the time spent on the water and the progression of full to new moon, suggesting that the birds may use moonlight to search for prey. Given its highly dispersed distribution at sea throughout the year, effective conservation of this threatened species may require management at large spatial scales.

Lesser black-backed gulls Larus fuscus are considered to be mainly pelagic. We assessed the importance of different landscape elements (open sea, tidal flats and inland) by comparing marine and terrestrial foraging behaviours in lesser black-backed gulls breeding along the coast of the southern North Sea. We attached GPS data loggers to eight incubating birds and collected information on diet and habitat use. The loggers recorded data for 10–19 days to allow flight-path reconstruction. Lesser black-backed gulls foraged in both offshore and inland areas, but rarely on tidal flats. Targets and directions were similar among all eight individuals. Foraging trips (n = 108) lasted 0.5–26.4 h (mean 8.7 h), and ranges varied from 3.0–79.9 km (mean 30.9 km). The total distance travelled per foraging trip ranged from 7.5–333.6 km (mean 97.9 km). Trips out to sea were significantly more variable in all parameters than inland trips. Presence in inland areas was closely associated with daylight, whereas trips to sea occurred at day and night, but mostly at night. The most common items in pellets were grass (48%), insects (38%), fish (28%), litter (26%) and earthworms (20%). There was a significant relationship between the carbon and nitrogen isotope signals in blood and the proportional time each individual spent foraging at sea/land. On land, gulls preferentially foraged on bare ground, with significantly higher use of potato fields and significantly less use of grassland. The flight patterns of lesser black-backed gulls at sea overlapped with fishing-vessel distribution, including small beam trawlers fishing for shrimps in coastal waters close to the colony and large beam-trawlers fishing for flatfish at greater distances. Our data show that individuals made intensive use of the anthropogenic landscape and seascape, indicating that lesser black-backed gulls are not a predominantly marine species during the incubation period.