The iconic Red-billed Tropicbird is a large seabird that spends most of its life far out at sea foraging for food. Tropicbirds are plunge divers, hunting for prey such as squid and flying fish. These birds can live up to around 20 years and lay just one egg per season. There are estimated to be around 8,000 pairs of tropicbirds globally, 40% of which nest on the islands of Saba and Statia. Given the significance of this number, it is easy to see how important these small islands are to the global population.
Unfortunately, these birds are falling prey to predators, many introduced by humans, which is having a negative impact on nesting success. To measure this impact, STENAPA, the group that manages the national parks of St. Eustatius, conducted a study to assess the breeding success of the Red-billed Tropicbird.
The study showed that across the nesting colonies studied, the tropicbird population had an average apparent hatching success of 60%, and an apparent fledging (birds leaving the nest) success of almost 80%. This puts breeding success at just under 50%, which means that less than half of the birds breeding are successful at producing young that will likely make it into adulthood.
More work needs to be done on assessing threats, since it is not clear what is the major cause of low nesting success. STENAPA has plans to use cameras to document the progress of suitable nests and gather information on the timing and frequency of egg loss. They also do an assessment of predators, namely rats, cats and land crabs.
For more information on this project, click here to read STENAPA’s most recent newsletter.