Mardik Leopold

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_...

Even though there are very many scattered seabird sighting records for the pelagic waters of the wider Caribbean Sea, only few studies bring these data together to generate a more comprehensive understanding of seabird use of the offshore areas of the region. The same is the case for the Dutch Caribbean EEZ which amounts to about 92 thousand km2 of the Caribbean Sea. As a consequence, information on seabird use of offshore waters has been identified as a key knowledge gap and research priority for both EEZ conservation and management purposes (Jongman et al. 2010, Meesters et al. 2010) and in support of a Bonaire-Curacao UNESCO World Heritage nomination that has been a Bonaire government ambition since 2003 (Debrot et al. 2017).  
 
In this project we followed up on these information needs by compiling many older but as-yet unpublished seabird records around the Dutch Caribbean islands, the eastern Caribbean as well as many poorly accessible seabird records for the waters off the coasts of Colombia and Venezuela. The most important additions of previously unavailable or new records for the eastern Caribbean were as follows: 1824 records by Poppe (1974), 627 by Halewijn (1972), 443 recent records by M. de Boer and J. Saulino (2014) all principally for the waters of the Dutch Caribbean, 547 records from Casler and Lira (1979) and Casler and Pirela (2004) for the northwestern sector of Venezuela and 249 records by Naranjo (1979) and Estela et al. (2004) for the Caribbean coast of Colombia. These were subsequently merged with several smaller and larger sources of seabird sighting records to yield a current total compilation of 150,372 sighting records with either exact or approximate position determinations. 
 
The database provides temporal and positional occurrence information for 65 nominate species and 13 larger familial or generic species groups in the Caribbean basin. As such, it provides a major new opportunity for the WUR to study and publish on various aspects of seabird distribution in the coming years. The potential topics include: 1) the community composition of the pelagic seabirds of the Caribbean in comparison with the community structure of other pelagic seabird communities, 2) how different habitat features (such as upwelling areas, proximity of nesting and/or roosting areas) are used by different species, 3) the identification of temporal trends in seabird species distribution and abundance, 4) identification of areas deserving conservation and management priority, either around seabird colonies or at the high seas. 

The Red-billed Tropicbird, a unique seabird that largely nests on Saba, direly needs more protection from predators such as feral cats and rats. Scientists Mardik Leopold and Michiel Boeken from the Netherlands were on Saba for four weeks to study and ring the tropicbirds.

Article originally published in BioNews 31