No abstract

Understanding how animals respond to atmospheric conditions across space is critical for understanding the evolution of flight strategies and long-distance migrations. We studied the three-dimensional movements and energetics of great frigate birds (Fregata minor) and showed that they can stay aloft for months during transoceanic flights. To do this, birds track the edge of the doldrums to take advantage of favorable winds and strong convection. Locally, they use a roller-coaster flight, relying on thermals and wind to soar within a 50- to 600-meter altitude band under cumulus clouds and then glide over kilometers at low energy costs. To deal with the local scarcity of clouds and gain longer gliding distances, birds regularly soar inside cumulus clouds to use their strong updraft, and they can reach altitudes of 4000 meters, where freezing conditions occur.

Marine Protected Areas (MPAs) are being established across all marine regions but their validity for the conservation of highly mobile marine vertebrates has been questioned. We tested the hypothesis that French coastal MPAs primarily designed for coastal and benthic biota are also beneficial for the conservation of a pelagic seabird, the Vulnerable yelkouan shearwater (Puffinus yelkouan), an endemic species to the Mediterranean Sea. We used a vast spectrum of electronic devices (GPS, temperature-depth-recorders, satellite transmitters and geolocators) and stable isotopic analyses to study the year-round movements and the trophic status of yelkouan shearwaters from the Hyères archipelago (France). In addition we conducted large-scale ship and aircrafts observation surveys to investigate spatio-temporal density patterns of shearwaters (genus Puffinus) in the western Mediterranean Sea. This extensive investigation permitted the first comprehensive study of the at-sea ecology of yelkouan shearwaters showing strikingly coastal habits, partial migration, unsuspected diving capabilities (max dive depth of 30 m), and a broad diet ranging from zooplankton to small pelagic fish. Importantly, 31% of yelkouan shearwaters GPS positions associated with foraging, 38% of diving positions, and 27% of resting positions were within the three French MPAs during the breeding season. These high scores confirmed by year-round distribution derived from GLS, PTTs, atsea and aerial observations, validated our hypothesis of the major importance of coastal MPAs for the conservation of yelkouan shearwater. Our case-study is therefore a major contribution to research efforts aiming at linking the spatial ecology of highly mobile marine vertebrates with effective conservation of marine biodiversity.

While interspecific differences in foraging behaviour have attracted much attention, less is known about how foraging behaviour differs between populations of the same species.Here we compared the foraging strategy of a pantropical seabird, the red-footed booby Sula sula, in 5 populations breeding in contrasted environmental conditions. The foraging strategy strongly differed between sites, from strictly diurnal short trips in Europa Island (Mozambique channel) to long trips including up to 5 nights at sea in Genovesa Island (Galapagos archipelago). The Expectation Maximisation binary Clustering (EMbC) algorithm was used to determine the different behaviours of individuals during their foraging trips (travelling, intensive foraging, resting and relocating). During the day, the activity budget was similar for all the breeding colonies. During the night, birds were primarily on the water, drifting with currents. At all sites, birds similarly performed intensive foraging in zones of area-restricted search (ARS), although the size and duration of ARS zones differed markedly. Red-footed boobies foraged over deep oceanic waters, with chlorophyll a concentrations varying between sites. Birds did not appear to target areas with higher productivity. We suggest that range differences between populations may be linked to other factors such as intra-and interspecific competition.

In the context of climate change, how extreme climatic events, such as cyclones, will affect the foraging abilities of marine vertebrates is still poorly known. During the course of a study on the foraging behaviour of two tropical seabirds, red-footed boobies and great frigatebirds, several cyclones have affected their breeding grounds and foraging zones, allowing us to study their response to extreme wind conditions. We examined whether adults and young naïve birds were able to predict the arrival of a cyclone and behave accordingly to reduce mortality risks and optimise foraging. We show that when a cyclone approached, juveniles and adults of the two species differed in their decisions to leave the colony for the sea. When the winds reached gale force, the juveniles of both species and adult frigatebirds remained at the colony, whereas adult boobies continued their foraging routine. The mortality of the individuals remaining on land remained limited. When encountering at-sea gale conditions, adult birds were able to avoid the centre of the low pressure systems and moved westward to bypass the route of the cyclones and circumvent the moving cyclone. Frigatebirds climb to high altitudes when close to the eye of the cyclone to bypass it at high speeds. These movements likely reduce the mortality risk at sea but can temporarily cause birds to move outside their normal range at sea or over land masses. We discuss the potential consequences of an increase in cyclonic conditions on seabird populations.

The early life stages represent a crucial period that can strongly influence population dynamics. We studied the development of foraging behaviour in the red-footed booby, a tropical seabird with an extensive post-fledging care period (3 to 6 months). Adults and juveniles were observed from shore and tracked at sea using GPS loggers over 3 consecutive 12-day periods. Juveniles initially made a majority of flights inland, likely to practice flying, and formed groups of up to 10 juveniles before making short trips at sea. They left the island later and returned earlier than the adults, allowing them to be fed on the nest. Over time, juveniles left the colony alone more frequently and increased the range of their trips while remaining significantly closer to the colony than the adults. They spent more time intensively foraging (slow and sinuous trajectory) than adults, which could reflect attempts to capture prey. Juveniles foraged independently of their parents but associated frequently with congeners, particularly during area-restricted search (ARS) behaviour. The extensive post-fledging care period observed may be explained by the need to develop proper foraging skills adapted to tropical waters, where resources are particularly scarce and unpredictable.

The wedge-tailed shearwater (WTS) population of New Caledonia is one of the largest in the world, yet its biology and foraging ecology are poorly known. We studied WTS from 4 colonies in New Caledonia. We examined foraging behaviour and habitats using GPS receivers and light sensors during and outside the breeding season, respectively, and compared our findings with those from other WTS populations worldwide. During breeding, New Caledonian WTS alternated short foraging trips close to the colony over the lagoon, or off the reef edge, with longer trips over distant, deep waters. Whereas neighboring colonies overlapped at sea, especially during short trips, there was a clear separation of foraging zones between the pairs of colonies located in the southern versus northwestern parts of New Caledonia. Although WTS actively foraged and commuted to foraging zones during the day, they mainly returned to the colony or rested at night, indicating that they feed mainly during the day. Active foraging did not take place in more productive areas, suggesting that it may instead be related to the presence of sub-surface predators. Outside the breeding season, birds from 3 colonies had similar trans-equatorial migratory behaviour. All left New Caledonia at the same time of the year with a fast, northeasterly movement and wintered over deep waters in the same sector of the northwestern tropical Pacific Ocean. At overwintering sites, they spent most of their non-foraging time presumably sitting on the water, especially at night, making a slow westward movement before returning to New Caledonia. WTS from New Caledonia forage over warm, oligotrophic deep waters throughout their life cycle, and the species appears to have a flexible foraging strategy adapted to the various environmental conditions encountered across its wide tropical range.

The early life of animals is a period of high mortality, when foraging capacities are assumed to be improved progressively. In birds, this critical period involves the improvement of the flight. How do young birds gain these capacities has rarely been studied in natural conditions especially in seabirds that spend most of their life at sea. We used detailed GPS and body acceleration data on 37 great frigatebirds (Fregata minor), to test the hypothesis that juveniles starting their first flights have lower flying capacities than adults, but that these capacities will improve during a long learning period, before independence from parents, specific to this seabird that can spend months on the wing at sea. We found that most flight components improved over time to tend towards those of adults, especially the travel speed, range, duration and maximum altitude of trips. However, unexpectedly, juveniles had higher ascent rates, soaring and gliding capacities above the sea than adults. Moreover, energy expenditure of juveniles was similar to adults during low cost travelling movements and during active foraging, but juveniles spent more time foraging actively than adults. Our results suggest that flight tactics based on long‐distance effortless movements specific to this family are acquired during a long period, but soaring and gliding capacities are already inherited by juveniles and possibly favoured by morphological adaptations specific to juveniles. These adaptations might explain the extreme dispersive capacities of juveniles.