seabirds

Abstract

Here, we document major seabird breeding recovery on a satellite island of Curaçao in the southern Caribbean following the removal of goats in 1997, significant reforestation from 2000–2005, and the extermination of cats in 2001. The only seabird to have been confirmed to breed on the island since the 1960s and until recently has been the Least Tern (Sternula antillarum). However, we now confirm nesting for an additional eight sea- and shorebird species on the island for the first time based on field observations in 2021 and 2022. The total number of documented nesting pairs annually has increased from a maximum of 140 pairs (of a single species in 2002), to > 430 pairs (of all species combined) in 2021 and 650 pairs in 2022. The dominant species are the Cayenne Tern (Thalassaeussandviscensis), Laughing Gull (Larus atricilla), Sooty Tern (Onychoprion fuscatus), and Least Tern, in that order. Breeding by the SootyTern and Bridled Tern (Onychoprion anatheus) are new national records for Curaçao. Klein Curaçao is now the island group’s most diverse and active seabird breeding location. Major threats to the nascent recovery of seabird breeding in this Ramsar-designated wetland area are the growing and uncontrolled human recreation, the repeated threat of reintroduction of feral cats, and predation by rats. Recommendations are made on measures needed to address these threats. The case study of Klein Curaçao demonstrates the potential for seabird recovery when deleterious invasive mammals are eradicated from islands.

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 ray-finned 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.

Full article available here: https://bioone.org/journals/ardea/volume-111/issue-2/arde.2022.a14/Forag...

During the HNLMS 'TYDEMAN' bathymetric expedition on the Saba Bank, April - May 1996, two observers spent 7 weeks on board and to collect data on the distribution of
seabirds, marine mammals, and human activities (fishing, shipping). The results show that the Saba Bank has a bird fauna that is relatively rich as compared with the surrounding seas, whilst the birds seem to be concentrated along the edges of the Bank. Observed cetaceans included three dolphin and one whale species. The bird and cetacean observations were made during a transitional season in which groups of animals are migrating into the area whilst others are migrating out.
Human activities included fishing (the distribution of fish pots was determined, and the activities of a few fishermen observed) and shipping. Especially the observation of large
tankers anchoring close to the edge of the Bank in areas where coral reefs occur, was identified as a threat.

The report presents the primary results of an opportunistic project which has yielded many rough but valuable data about the Saba Bank in April-May. These data are available
for future management of the Saba Bank. The preliminary elaboration of the data in this report confirm the importance of especially the edges of the the Saba Bank for birds and
suggest the Bank being a feeding area for populations that breed on the neighbouring islands. Together with the observations of different species of cetaceans, the results
confirm the idea that the Saba Bank has considerable importance or the marine biodiversity in the region of the leeward Antilles. The position of the Saba Bank, partly
within the territorial waters of the Netherlands Antilles but completely within the limits of a hypothetical Exclusive Economic Zone, offers a great promise that protection (and sustainable use) of these natural values can be legally effected.