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Due to rapidly changing global environmental conditions, many animals are now experiencing concurrent changes in both resource availability and the foraging cues associated with finding those resources. By employing flexible, plastic foraging strategies that use different types of environmental foraging cues, animals could adapt to these novel future environments. To evaluate the extent to which such flexibility and plasticity exist, we analyzed a large dataset of a clade (Sulidae; the boobies) of widespread aerial tropical predators that feed in highly variable marine habitats. These surface foragers are typical of many ocean predators that face dynamic and patchy foraging environments and use a combination of static and ephemeral oceanographic features to locate prey. We compared foraging habitats and behaviors of four species at seven colonies in the eastern and central Pacific Ocean that varied greatly in depth, topography, and primary productivity. Foraging behaviors, recorded by GPS‐tracking tags, were compared to remotely sensed environmental features, to characterize habitat‐behavior interactions. K‐means clustering grouped environmental characteristics into five habitat clusters across the seven sites. We found that boobies relied on a combination of static and ephemeral cues, especially depth, chlorophyll‐a concentrations, and sea surface height (ocean surface topography). Notably, foraging behaviors were strongly predicted by local oceanographic habitats across species and sites, suggesting a high degree of behavioral plasticity in use of different foraging cues. Flexibility allows these top predators to adapt to, and exploit, static and ephemeral oceanic features. Plasticity may well facilitate these species, and other similarly dynamic foragers, to cope with increasingly changing environmental conditions.

Seabirds are often free from blood parasites, and a recent review suggested that phylogenetic, ecological and life-history parameters can determine the prevalence of blood parasites in seabirds. However, there is a lack of data available from many seabird groups, and a larger database is needed to understand prevalence patterns of blood parasites. We used a molecular screening approach to detect parasites of the genera Plasmodium, Haemoproteus, Leucocytozoon and Babesia in five species of two genera of seabirds that breed on Atlantic Ocean islands off Brazil. The observed patterns differed between the two bird genera. Like other Laridae, brown noddy, Anous stolidus adults were infected with Haemoproteus with low prevalence. Masked boobies, Sula dactylatra and brown boobies, Sula leucogaster were infected with Babesia. Of the latter, mainly juveniles were infected. In all species, intensity of infection (i.e. number of infected erythrocytes) was so low that parasites remained undetected in blood smears. This may explain the absence of major effects on the body condition of birds, although infected juvenile masked boobies were lighter than juveniles that were not infected with Babesia. Two tree-nesting species; black noddy, Anous minutus and red-footed booby, Sula sula did not have blood parasites, suggesting that tree-nesting may reduce the exposure to arthropod vectors compared with ground nesting in these species.

Seabirds are one of the most threatened avian taxa and are hence a high conservation priority. Managing seabirds is challenging, requiring conservation actions at sea (e.g. Marine Protected Areas - MPAs) and on land (e.g. protection of breeding sites). Important Bird and Biodiversity Areas (IBAs) have been successfully used to identify sites of global importance for the conservation of bird populations, including breeding seabirds. The challenge of identifying suitable IBAs for tropical seabirds is exacerbated by high levels of dispersal, aseasonal and asynchronous breeding. The western Indian Ocean supports ~19 million breeding seabirds of 30 species, making it one of the most significant tropical seabird assemblages in the world. Within this is the British Indian Ocean Territory (BIOT), encompassing 55 islands of the Chagos Archipelago, which supports 18 species of breeding seabird and one of the world’s largest no-take MPAs. Between January and March in 1975 and 1996, eight and 45 islands respectively were surveyed for seabirds and the data used to designate 10 islands as IBAs. A further two were proposed following an expedition to 26 islands in February/March 2006. Due to the historic and restricted temporal and spatial nature of these surveys, the current IBA recommendations may not accurately represent the archipelago’s present seabird status and distribution. To update estimates of the BIOT breeding seabird assemblage and reassess the current IBA recommendations, we used seabird census data collected in every month except September from every island, gathered during 2008–2018. The maximum number of breeding seabirds for a nominal year was 281,596 pairs of 18 species, with three species making up 96%: Sooty Tern Onychoprion fuscatus - 70%, Lesser Noddy Anous tenuirostris - 18% and Red-footed Booby Sula sula - 8%. Phenology was a complex species-specific mix of synchronous and asynchronous breeding, as well as seasonal and aseasonal breeding. Nine of the 10 designated IBAs and the two proposed IBAs qualified for IBA status based on breeding seabirds. However, not every IBA qualified each year because Sooty Terns periodically abandoned breeding islands and Tropical Shearwater Puffinus bailloni breeding numbers dropped below IBA qualifying criteria in some years. Further, one survey per year does not always capture the periodic breeding of some tropical seabirds. We propose therefore, that IBAs in BIOT are better designated at the island cluster level rather than by specific island and require two surveys six months apart per year. This work highlights the merits of long-term, systematic, versus incidental surveys for breeding tropical seabirds and the subsequent associated designation of IBAs.

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 stronglydiffered between sites, from strictly diurnal short trips in Europa Island (Mozambique channel) tolong trips including up to 5 nights at sea in Genovesa Island (Galapagos archipelago). The ExpectationMaximisation binary Clustering (EMbC) algorithm was used to determine the differentbehaviours of individuals during their foraging trips (travelling, intensive foraging, resting andrelocating). During the day, the activity budget was similar for all the breeding colonies. Duringthe night, birds were primarily on the water, drifting with currents. At all sites, birds similarly performedintensive foraging in zones of area-restricted search (ARS), although the size and durationof ARS zones differed markedly. Red-footed boobies foraged over deep oceanic waters, withchlorophyll a concentrations varying between sites. Birds did not appear to target areas withhigher productivity. We suggest that range differences between populations may be linked toother factors such as intra- and interspecific competition.

It is common for marine animals to be selective in the amount and quality of foods during reproduction due to the higher energetic demands. As central place foragers, seabirds are often selective with the prey species they deliver to their offspring. We evaluated trophic segregation between parents and their offspring in blue-footed booby (Sula nebouxii) by measuring stable isotope ratios ( delta super(15)N and delta super(13)C) in blood samples during two breeding seasons and at different reproductive stages (incubation, early and late chick rearing). Additionally, we examined if delta super(15)N values from chicks were correlated with their condition as reflected in blood alkaline phosphatase (ALP) levels. delta super(15)N values increased and delta super(13)C values decreased in adults as the breeding season progressed, indicating differences in foraging regions or the assimilated prey. delta super(15)N values differed significantly between sexes; males had higher delta super(15)N values than females during all reproductive stages sampled during the 2011 season, whereas in 2012 the difference between sexes was only observed during incubation. Offspring had higher delta super(15)N values and lower delta super(13)C values than adults, suggesting that, when feeding their chicks, parents feed them with prey from higher trophic levels and possibly from more oceanic environments. ALP levels, a proxy for bone growth and condition, measured in the offspring were positively correlated with delta super(15)N values during the chick-rearing period. Although the diet of parents differed between reproductive stages, a multi-source Bayesian mixing model indicated that their primary prey were Pacific anchovy and halfbeaks, with a combined modal fractional contribution of 50-70% of the diet. The diet of the offspring was dominated by Pacific anchovy ( approximately 36%), which was also the prey with the highest lipid content (C:N ratio 5.57), whereas the contributions of other fish species (or groups) were similar (17-24% each). Our findings suggest that parents actively feed their young with high-quality prey, which seems to increase some of the individual fitness components associated with better growth.

Inter- and intraspecific competition can lead to resource partitioning in sympatric species, processes likely affected by environmental productivity and population size. We investigated the foraging behaviour and diet of masked (Sula dactylatra) and red-footed (S. sula) boobies at Tromelin Island, western Indian Ocean, to examine the role of resource partitioning in the foraging strategies of these sympatric species in an extreme oligotrophic environment. We compared our results to published studies with differing environmental conditions or population sizes. We used GPS loggers and Argos transmitters to track foraging movements and used time-depth recorders to estimate dive depths. Masked boobies travelled further and at faster rates than red-footed boobies, and sexes did not differ in foraging behaviour. Based on randomization tests, the foraging range of each species (95% utilization distribution; UD) overlapped significantly. However, at core foraging areas (50% and 25% UD), interspecific segregation was greater than expected by chance alone. No intraspecific spatial segregation was detected between sexes. Environmental characteristics of area-restricted search zones differed between species, but not sexes; masked boobies utilized warmer, deeper, and less windy oceanic environments than red-footed boobies. Masked boobies attained greater diving depths than red-footed boobies and consumed primarily flying fish, whereas red-footed boobies consumed mostly squid. Red-footed and masked boobies breeding in the extreme oligotrophic environment near Tromelin demonstrated greater dietary partitioning differences in foraging ranges compared to a less oligotrophic environment. This suggests that environmental productivity may play a role in processes of resource partitioning in these sympatric species.

Comprehending how environmental variability shapes foraging behaviour across habitats is key to unlocking insights into consumer ecology. Seabirds breeding at high latitudes are exemplars of how marine consumers can adapt their behaviours to make use of predictable foraging opportunities, but prey tends to be less predictable in tropical oceanic ecosystems and may require alternative foraging behaviours. Here we used GPS and time-depth recorder loggers to investigate the foraging behaviour of central placed adult red-footed boobies ( Sula sula rubripes ), a tropical seabird that forages in oceanic waters via diving, or by capturing aerial prey such as flying fish in flight. Dive bout dynamics revealed that red-footed boobies appeared to exploit denser, but more sparsely distributed prey patches when diving further from the colony. Furthermore, although we found no evidence of environmentally driven habitat selection along their foraging routes, red-footed boobies preferentially dived in areas with higher sea surface temperatures and chlorophyll-a concentrations compared to conditions along their foraging tracks. This multi-scale variation implies that habitat selection differs between foraging routes compared to dive locations. Finally, red-footed booby dives were deepest during the middle of the day when light penetration was greatest. Ultimately, we highlight the importance of gaining insights into consumer foraging across different ecosystems, thereby broadening understanding of how animals might respond to changing environmental conditions.

The red-footed booby (Sula sula) is one of the most common pantropical seabird species, but its populations have been declining in the Caribbean region and elsewhere. We used distance sampling from point-counts to estimate population size of red-footed boobies in Mona Island, Puerto Rico, USA, before and during the breeding season in 2019. We compared results from early morning and early night surveys to determine the best survey time given that many individuals are foraging at sea during the daylight hours but not at night. We also examined the suitability of drone photography to survey active nests (a measure of breeding pairs) and compared it to point count and transect survey data. Point count surveys show that an estimated 6,130 birds occupied the colony, which is more than double previous estimates for Mona Island. Our results also showed that to avoid underestimates, red-footed booby colonies are best surveyed at night as they yield higher bird densities than daytime surveys. For the same reason, daytime photographic surveys with a drone underestimated population size compared to nighttime point-count surveys. However, drones were more effective than ground surveys in detecting active nests, and thus breeding pairs, which provides a better estimate of the resident population of a colony. We recommend that nighttime surveys are tailored to site-specificconditions to improve estimates of red-footed boobies, while drones can save significant effort and time in monitoring numbers of active nests in the remote and rugged islands where red-footed boobies typically nest.

Sympatric species with similar ecological requirements and differences in body size would be expected to partition resources to facilitate coexistence. For sexually dimorphic species, we may expect resource partitioning by gender as well as by species identity. However, it is difficult to document species and sexual resource partitioning in marine ecosystems, given the intractability of these systems and the vagility of many marine animals. Here, we examined differences in the foraging behavior and prey selection of 2 congeneric and coexisting seabird species—masked boobiesSula dactylatraand red-footed boobiesSula sula—on Palmyra Atoll in the equatorial Pacific Ocean. These seabirds exhibit substantial size dimorphism between species and also have reverse sexual dimorphism within species. Pronounced interspecific differences in foraging patterns were observed with high-resolution GPS tracking devices, where smaller red-footed boobies conducted longer foraging trips (in both time and distance). Red-footed boobies also had more frequent landings on the sea surface, slower mean and maximum travel speeds, and more westerly trip azimuths. Stable isotope and diet analyses produced data that complemented returns from electronic tagging. Stable isotope ratios of carbon indicated that masked boobies foraged on prey with a less pelagic δ13C signature compared to red-footed boobies. In contrast, no gender differences were identified in any foraging parameters. The mechanisms for maintenance of these pronounced differences in niche partitioning across species were not explicitly examined, yet the data suggest physiological variation across species may be a more plausible mechanism than competitive interactions.

Effective seabird conservation requires understanding their marine spatial ecology. Tracking can reveal details of their foraging ecology and habitat use, as well as the suitability of marine protected areas for at-sea conservation, but results are often regionally specific. Here we characterised the foraging behaviour of tropical breeding brown boobies Sula leucogaster in the Chagos Archipelago, Western Indian Ocean, and tested habitat requirements. GPS tracking of thirteen individuals from two colonies, located 142 km apart on the same atoll (Great Chagos Bank), showed similar foraging effort and habitat preferences despite differences in season and breeding stage. Brown boobies from both tracked populations foraged close to the colony along the atoll shelf edge, avoiding deep oceanic areas and shallow waters of the Great Chagos Bank atoll, but within the Chagos Archipelago Marine Protected Area. Sea-level height anomaly and sea surface temperature were important foraging predictors at both sites, although birds experienced distinct environmental conditions between colonies. These results suggest that while brown boobies have colony-specific at-sea foraging areas, similarities in habitat drivers of distribution and foraging behaviour can inform predictions of distributions at other colonies within the archipelago, with important benefits for at-sea conservation efforts.