Diet

Abstract

Prey resources in oligotrophic tropical marine environments are often scattered and unpredictable. Tracking studies of tropical seabirds can provide critical information about ocean habitat affinities, prey choice and the utilisation of surrounding areas, which can be useful for conservation managers. Foraging studies of Red-billed Tropicbird populations in the Caribbean are scarce but increasing. We sought to expand on this by tracking chick-rearing adults using GPS devices and subsequently linking these tracking data to remotely-sensed environmental variables. We related our spatial data to opportunistic sampling of regurgitates in a globally significant nesting colony on Saba, Caribbean Netherlands. Diet samples were dominated by flying fish (Exocoetidae; numerical frequency: 70.73%), but prey items from the squid family (Loliginidae; 9.76%) and the families of flying gurnards (Dactylopteridae; 2.44%) and the rayfinned fish (Carangidae; 2.44%) were also identified, although we were unable to identify 14.63% of samples due to digestion. An additional goal of our study was to compare the foraging ecology of Tropicbirds on Saba with those nesting on St. Eustatius, located circa 25 km south-east. As expected, Tropicbirds nesting on Saba exhibited diurnal foraging patterns, travelling a maximum distance from the colony of 553.7 km, with an average trip length of 117.2 ± 144.6 km (±SD). Adults foraged in shallower, cooler waters with higher chlorophyll a concentrations and higher Exocoetidae species richness compared to travelling points. Despite the proximity of Saba and St. Eustatius, this is contrary to what was found for Tropicbirds nesting on St. Eustatius, where adults foraged in deeper waters with a low Exocoetidae species richness. However, Tropicbirds from Saba and St. Eustatius did exhibit some similarities in their foraging behaviour; specifically, foraging adults traversed multiple exclusive economic zones and marine protected areas, reinforcing our recommendation for nature managers in the Caribbean to create a transboundary network in order to effectively protect and conserve this species.

Investigating the foraging patterns of tropical seabirds can provide important information about their ocean habitat affinities as well as prey choice. Foraging studies of Red-billed Tropicbird Phaethon aethereus populations in the Caribbean are lacking. We sought to rectify this by opportunistically sampling regurgitates at nest sites on the island of St. Eustatius, Lesser Antilles, and by linking the GPS tracks of foraging adults to remotely sensed environmental variables. Diet samples were dominated by Exocoetidae (59.5%) and Belonidae (14.9%), although we were unable to identify 25.5% of samples due to digestion. Tropicbirds nesting on St. Eustatius exhibited diurnal foraging patterns, foraged in deeper waters with higher chlorophyll concentration, and consumed fewer Exocoetidae species compared to travelling behaviour. The maximum distance travelled from the colony was 953.7 km, with an average trip length of 176.8 (± 249.8) km. The biologged birds crossed multiple exclusive economic zones and marine protected areas, and on that basis, we suggest that efforts to protect and conserve this species may require transboundary collaboration throughout the wider Caribbean.

Investigating the foraging patterns of tropical seabirds can provide important information about their ocean habitat affinities as well as prey choice. Foraging studies of Red-billed Tropicbird Phaethon aethereus populations in the Caribbean are lacking. We sought to rectify this by opportunistically sampling regurgitates at nest sites on the island of St. Eustatius, Lesser Antilles, and by linking the GPS tracks of foraging adults to remotely sensed environmental variables. Diet samples were dominated by Exocoetidae (59.5%) and Belonidae (14.9%), although we were unable to identify 25.5% of samples due to digestion. Tropicbirds nesting on St. Eustatius exhibited diurnal foraging patterns, foraged in deeper waters with higher chlorophyll concentration, and consumed fewer Exocoetidae species compared to travelling behaviour. The maximum distance travelled from the colony was 953.7 km, with an average trip length of 176.8 (± 249.8) km. The biologged birds crossed multiple exclusive economic zones and marine protected areas, and on that basis, we suggest that efforts to protect and conserve this species may require transboundary collaboration throughout the wider Caribbean.

The lunar cycle is a key environmental factor influencing the feeding, reproduction, and migration of many marine organisms, including fish, invertebrates, and zooplankton. To investigate the influence of lunar stage on zooplankton density and diversity in Bonaire, Netherlands Antilles, samples of zooplankton were collected from surface waters at midday and at night at each stage of a complete lunar cycle. The purpose of this research was to determine 1) whether zooplankton in surface waters are more abundant during the night or day, 2) during which stage in the lunar cycle zooplankton densities are the highest, 3) whether diel period has an effect on the biodiversity of plankton, and 4) whether lunar stage has a effect on biodiversity of zooplankton. It was found that microzooplankton and macrozooplankton occurred in higher densities at night. The highest microzooplankton density occurred during the waning gibbous phase and the highest macrozooplankton density occurred during the first quarter (289.7 individuals m-3, 28.4 individuals m-3, respectively). Organisms from the classes maxillopoda, malacostraca, and chaetognatha were most prevalent in all samples. The full moon showed both the greatest and least taxonomic diversity among samples with 19 different classes (avg. 13.4) found during the nighttime sample and 7 appearing during the midday sample. Due to an abundance of eggs during the waning gibbous lunar stage it is suggested that lunar spawning has an impact on plankton density and composition.

This student research was retrieved from Physis: Journal of Marine Science VI (Fall 2009)19: 27-34 from CIEE Bonaire.

The estimated number of species of Moray Eels (Family: Muraenidae) worldwide is around 200. A majority of morays hide in crevices and holes during the day, but come out to forage at night. The amount of activity during the day and night differs between species. Some are strictly nocturnal or diurnal while others are equally present during both times. Morays are generally piscivores and have large impacts on the biomass of reef fishes due to their maneuverability. In some studies, morays have been found to have the largest impact out of all other piscivores regarding the quantity of fishes consumed. In this study we dove at 15 m for 45 min during the day and at sunset three times each (six dives total). We also snorkeled the same distance covered while diving, but shallower along the shoreline. The number and species of moray within a 2-m band while diving and a 1m band while snorkeling were recorded. Spotted morays were the most common species seen overall (87.3% of all morays recorded). The density of morays was the highest while snorkeling (1.38 ± 0.77/10 m2 ). The density of morays while snorkeling was roughly 10 times greater than the day dives and almost 14 times greater than the sunset dives. Smaller morays were seen in the shallows while snorkeling and larger morays were seen while diving. The high number of small morays seen shallower indicates that morays may use shallow habitats as juveniles and move deeper on the reef once they mature and can consume larger prey.

This student research was retrieved from Physis: Journal of Marine Science XVIII (Fall 2015)19: 21-26 from CIEE Bonaire.

Two bat species, Leptonyrteris curasoae and Glossophaga longirostris, are the principal pollinators of at least two of the three species of columnar cacti that grow on the semiarid island of Curaçao, Netherlands Antilles. I examined the importance of the cacti in the diets of the bats and found that 85–91 percent of their diet samples contained cactus pollen and seeds. At least 43 percent of the samples from each species contained cactus pollen andlor seeds exclusively. Leptonycteris curasoae consumes nectar and pollen of Ceiba pentandra and Agave spp. at the beginning of the dry season and G. longirostris also consumes a few other plant products in the wet season, but both bat species depend nutritionally on cacti. Female bats give birth to one pup per year, and the periods of parturition and lactation in each species correspond to peaks in the reproductive phenology of the two most abundant columnar cactus species. From personal observations and a review of the literature, I determined that bats were unlikely to fly to the mainland to feed, although L. curasoae may do so. I conclude that the interdependence of bats and cacti is suggestive of coevolution, and that columnar cacti are critical for the survival and persistence of nectar-feeding bats on Curaçao.

DOI: 10.1111/j.1744-7429.1997.tb00026.x