Conservation opportunities for tern species at two Ramsar sites on Bonaire, Caribbean Netherlands

Abstract

The island of Bonaire is a nesting location for at least four tern species: a subspecies of the Least Tern (Sternula antillarum
antillarum), the Common Tern (Sterna hirundo), the Royal Tern (Thalasseus maximus), and a subspecies of the Sandwich
Tern (Thalasseus sandvicensis eurygnathus). The island is also a significant nesting site for the Caribbean Least Tern (Sternula
antillarum) population. Our main objectives were to: a) measure and compare breeding success at five known nesting sites on
northern Bonaire, b) document and compare the impact of natural and introduced predators on each site, and c) give management
recommendations for increasing breeding success based on our results. Our nest counts from 2014 indicate a significant
decline in nest abundance compared to historical observations from the 1950s, matching previous studies and observations
from the last two decades. Among the five nesting sites in our study, terns at the two island sites had the largest number of
breeding pairs and achieved the greatest success, fledging a maximum of ~0.8 chicks per nest, compared to all other sites which
were connected to the shoreline. We recorded rats and cats as predators at the peninsula site and field observations suggested
that predation by Laughing Gulls (Leucophaeus atricilla) might also be occurring at two sites. Both natural and artificial islands
on hypersaline lagoons provide good nesting sites for terns on Bonaire as they are protected from mammalian predators. However,
recreational disturbance remains the single most serious and pervasive threat to the future of seabird nesting on Bonaire
and requires concerted action. We propose a list of management actions to increase the numbers of nesting terns throughout
the sites studied. Increasing protection from predators and human disturbance by making artificial nesting islands will provide
the potential for Bonaire, and its sister islands, to become major refuges for southern Caribbean metapopulations of these four
tern species.