Red-billed Tropicbird Phaethon Aethereus Research Articles

Distribution, abundance, and on-land threats to Cabo Verde seabirds

SummaryPelagic seabird populations have declined strongly worldwide. In the North Atlantic there was a huge reduction in seabird populations following the European colonization of the Azores, Madeira and Canary archipelagos but information on seabird status and distribution for the subtropical region of Cabo Verde is scarce, unavailable or dispersed in grey literature. We compiled and compared the historical and current distribution of all seabird species breeding in the Cabo Verde archipelago, updated their relative abundance, investigated their inland habitat preferences, and reviewed their threats. Currently, the breeding seabird community in Cabo Verde is composed of Bulwer’s Petrel Bulweria bulwerii, White-faced Storm-petrel Pelagodroma marina aedesorum, Cape Verde Shearwater Calonectris edwardsii, Cape Verde Storm-petrel Hydrobates jabejabe, Cape Verde Petrel Pterodroma feae, Boyd's Shearwater Puffinus lherminieri boydi, Brown Booby Sula leucogaster, and Red-billed Tropicbird Phaethon aethereus. One breeding species is currently extinct, the Magnificent Frigatebird Fregata magnificens. The relative abundance of Cape Verde Shearwater, Boyd’s Shearwater, Cape Verde Petrel, and Cape Verde Storm-petrel was determined from counts of their nocturnal calls in Santo Antão, São Vicente, Santa Luzia, Branco, Raso and São Nicolau. Cape Verde Petrel occurred only on mountainous islands (Santo Antão, São Nicolau, Santiago, and Fogo) from mid-to high elevations. Larger species such as the Cape Verde Shearwater and Boyd’s Shearwater exhibited a wider distribution in the archipelago, occurring close to the coastline but at lower densities on populated islands. Small procellariforms such as the Cape Verde Storm-petrel occurred at high densities only on rat-free islets and in steep areas of main islands where introduced cats and rats are unlikely to occur. The main threats to seabird populations in Cabo Verde range from predation by introduced predators, habitat alteration or destruction, and some residual human persecution.

Reproductive Performance, Mate Fidelity and Nest Cavity Fidelity in Red-Billed Tropicbirds Phaethon aethereus mesonauta on St. Eustatius, Caribbean Netherlands

Mate choice and nest cavity selection are directly linked to reproductive performance in seabirds, and disruption of these can result in breeding failure. The Red-billed Tropicbird Phaethon aethereus mesonauta breeds on inaccessible and remote islands, nesting primarily in natural rock cavities. I examined the relationship between reproductive performance and mate and nest cavity fidelity on St. Eustatius from 2012 to 2016, corresponding to four successive breeding seasons. The majority of nest failures occurred during the incubation stage. Pairs that failed in their first breeding attempt and laid a replacement clutch were more likely to be faithful to their mate and nest cavity within and between seasons than pairs that bred successfully. Only two replacement clutches (3.8%) were laid after the loss of a chick in the first breeding attempt, whereas the remaining 50 replacement clutches (96.2%) were laid after the loss of an egg. The stage at which pairs split had no influence on mate or nest cavity retention the following season. There were no significant differences in the weight or morphological measurements of chicks from pairs that retained their nest mate and/or cavity and those that switched. The results of this study suggest that switching nest mate or nest cavity does not necessarily improve subsequent breeding success among Red-billed Tropicbirds on St. Eustatius.

Breeding seabird populations in Brazilian oceanic islands: historical review, update and a call for census standardization

In recent decades, several seabird populations have declined globally due to anthropogenic activities. In Brazil, 14 seabird species breed at four oceanic islands and one atoll: the Abrolhos, Fernando de Noronha, and Sao Pedro and Sao Paulo (SPSPA) archipelagos; the Trindade/Martin Vaz Islands; and the Atol das Rocas. Seven species are listed as nationally threatened by extinction. This study aimed to present new information on breeding seabird populations in Brazilian oceanic islands, compile all available data previously published and, when possible, to provide updated information on population estimates from censuses carried out sporadically at different islands between 2006 and 2013. Based on new data and the thorough review provided here, of the 35 seabird breeding populations analysed, 14% were increasing (as Red-billed Tropicbird Phaethon aethereus , Magnificent Frigatebird Fregata magnificens and Brown Noddy Anous stolidus in Abrolhos), 11% were decreasing (as Brown Booby Sula leucogaster in Atol das Rocas and Great Frigatebird Fregata minor in Trindade Island), 23% were stable (as White-tailed Tropicbird Phaethon lepturus in Fernando de Noronha and Brown Noddy and Black Noddy Anous minutus in Sao Pedro and Sao Paulo Archipelago), and the remaining 49% were unknown or not possible to evaluate. The Red-footed Booby ( Sula sula ) is locally extinct in Trindade Island, however there are colonies of only a few individuals of other species, such as the Audubon's Shearwater Puffinus lherminieri and Red- billed Tropicbird in Noronha, Black Noddy in Martin Vaz, and Great ( Fregata ariel trinitatis ) and Lesser ( F. m. nicoll i) Frigatebirds in Trindade, that may become extinct soon. Censuses at distinct periods of the breeding cycles and protocols were highly variable, making temporal comparisons difficult. These results indicate an urgent need for long-term studies to improve the scenario to assess seabird population trends based on comparable methodologies, in order to determine trends in the future.

Important foraging areas of seabirds from Anguilla, Caribbean: Implications for marine spatial planning

Marine spatial planning (MSP) has become an important tool to balance the needs of commercial, economical and recreational users of the marine environment with the protection of marine biodiversity. BirdLife International advocate the designation of marine Important Bird Areas (IBAs) as a key tool to improve the protection and sustainable management of the oceans, including the designation of Marine Protected Areas, which can feed into MSP processes. This study presents the results of three years of seabird tracking from the UK Overseas Territory of Anguilla, where marine resources are currently relatively unexploited and MSP is in its infancy. The core foraging areas of 1326 foraging trips from 238 individuals, representing five species (brown booby Sula leucogaster, masked booby Sula dactylatra, sooty tern Onychoprion fuscatus, magnificent frigatebird Fregata magnificens and red-billed tropicbird Phaethon aethereus) breeding on three of Anguilla's offshore cays were used to calculate the hotspot foraging areas for each study species. These high activity areas were then compared with fishing activity within Anguilla's Exclusive Economic zone and to proposed coastal developments. Two marine IBAs were identified within Anguilla's waters: the first to be defined, using seabird tracking data, in the Caribbean region. Whilst the level of fishing activity and associated seabird by-catch is hard to quantify, the core foraging areas of seabirds breeding in Anguilla were observed to overlap with areas known for high fishing activity. These findings highlight the need to work both nationally and across territorial boundaries to implement appropriate marine spatial planning.

Role of body size in shaping the trophic structure of tropical seabird communities

Ecological segregation among coexisting seabird species can occur due to morpho- logical and behavioral differences. This segregation is especially important as it reduces competi- tion during the breeding season, when birds are central-place foragers. Furthermore, seasonal variation in oceanographic processes may change prey availability and shape seabird community trophic structure and species isotopic niche. We used stable isotope analyses of seabird whole blood and prey muscle in 5 tropical seabird communities representing 12 species (Charadri- iformes, Phaethontiformes, Procellariiformes and Suliformes) inhabiting 5 offshore islands off Brazil from 00°55' N to 20° 30' S and 65 to 1160 km from the coast. We evaluated how community trophic structure was correlated with morphology (body mass and bill length), and we verified seasonal variation in isotopic niche in 2 communities. Overall, seabird trophic position (TP) was positively correlated with body size, with frigatebirds and boobies occupying a higher TP than noddies and terns. Structuring of seabird communities according to body size probably occurred due to consumption of prey of different sizes and TP, which contributed to niche segregation by reducing interspecific competition during the breeding season. All species showed isotopic niche segregation at 2 islands, and ~60 to 70% of species segregated at the other islands, except at Atol das Rocas, where 43% of species segregated. Niche overlap occurred mainly among closely related species at Atol das Rocas, Fernando de Noronha and Trindade. The isotopic niche and TP changed across islands for all 3 boobies (red-footed Sula sula, brown S. leucogaster and masked S. dactylatra), brown noddy Anous stolidus and red-billed tropicbird Phaethon aethereus; these factors also changed seasonally in other species, such as in magnificent frigatebird Fregata mag- nificens, brown booby, both the red-billed P. aethereus and white-tailed P. lepturus tropicbirds and both the brown A. stolidus and black Anous minutus noddies. Such changes probably occurred due to differences in prey availability, opportunistic behavior (e.g. feeding on fishery dis- cards) and/or local foraging and diet specialization.