phaethon aethereus

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.

Abstract

Robert L. Norton encountered a Red-billed Tropicbird (Phaethon aethereus) approximately 60 km NNW of Aruba, providing Aruba’s first record of this species. Given the pelagic distribution of this species during the non-breeding season, and nine antecedent records from Bonaire and Curaçao, additional records seem likely for Aruba, especially given an increase in reports of seabirds from cruise ships off Aruba

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.

Abstract

The daily nest-survival rates of Red-billed Tropicbirds (Phaethon aethereus) were estimated over six breeding seasons on St. Eustatius in the Caribbean. We analyzed 338 nesting attempts between 2013 and 2020. The daily survival rate (DSR) of tropicbird nests was modeled as a function of nest initiation date, sea surface temperature (SST), elevation, vegetation in front of the nest, and year. Yearly nest survival rates (± SE) of the best fitting models ranged from 0.21 ± 0.06–0.74 ± 0.13 (n = 338 nests). DSR of the most parsimonious models averaged 0.39 ± 0.04 during the incubation period, 0.83 ± 0.05 during the chick-rearing period, and 0.30 ± 0.04 during the nesting period (incubation through fledging) when data were pooled across all years. Models with linear and quadratic trends of nest initiation date combined with SST and elevation received strong support in the incubation and nesting periods. Nests initiated in peak nesting season, when SSTs were lower, had higher DSR estimates than nests initiated early or late in the season. Compared to studies of the same species from Saba and the Gulf of California, survival probability on St. Eustatius was lower during the incubation stage but higher during the chick-rearing period. Similar to populations in the Gulf of California, tropicbird reproduction differed and laying date varied among years, and survival was influenced by SST. Our results are consistent with a study on White-tailed Tropicbirds (Phaethon lepturus) in Bermuda which found that survival was affected by temporal factors rather than physical site characteristics. Our study contributes to a better understanding of the factors that influence Red-billed Tropicbird survival on a small Caribbean island

https://www.researchgate.net/publication/365346690_Reproductive_Success_...

Abstract

Red-billed Tropicbirds have historically been considered rare visitors to the waters around the islands of Aruba, Curaçao, and Bonaire in the southern Caribbean. However, in recent years there has been an increase in documented records. We summarize all known Red-billed Tropicbird records for the region and review broader regional population and movement data to place this increase in records in context. We recommend continued careful documentation of Red-billed Tropicbird records on and around the islands of Aruba, Curaçao, and Bonaire and the implementation of a standardized monitoring pro-gram across the Caribbean range for the species to better understand the species' population status, trends, and breeding and at-sea distribution

Red-billed Tropicbirds breeding on Pilot Hill on the island of Sint Eustatius have been exhibiting an average survival rate of between 30-40%. The influence of nest cavity attributes, environmental covariates, and parent behavior on Red-billed Tropicbird survival were evaluated through nest surveys and camera trap data. Daily survival rate was calculated as a function of selected covariates. Time spent away from the nest by parents and minimum temperature were the most influential factors. Nest attributes and temperature variables did not correlate to survival.