Between 2008 and 2010, STINAPA Bonaire and volunteers took to counting Brown Booby seabirds along the northwestern coast of Bonaire. These numbers represent the first study of its kind in over 50 years and showed a slow increase in numbers since the establishment of the Washington Slagbaai National Park in 1969.

Brown Boobies (Sula leucogaster) are large seabirds, known to roost along cliff edges in the Caribbean. These birds typically nest in large colonies and plunge-dive to catch small fish and squid. Each season, these birds usually lay two eggs, but its common for only one to survive the first few months after hatching.

Brown Boobies on Bonaire

Although these birds can be seen on each of the ABC islands, they are not known to breed here. The northwest coast of Bonaire is a known roosting area, with reports dating as far back as the 1950s. Originally, around 200 Brown Boobies were known to use these cliffs as roosting areas, however, accounts of raids by fishermen could wipe out half of this population within a single hunt. These birds were often caught for food and for their liver, which was an important ingredient to be used in ‘bruha’ (black magic).

Luckily, since 1969, the areas around these roosting areas were designated a nature reserve, which would eventually become the Washington Slagbaai National Park managed by Stichting Nationale Parken Bonaire (STINAPA Bonaire). This designation meant that hunting these birds here was now illegal. Although hunting has officially been banned for nearly 50 years, no updated populations counts had been conducted since.

Brown Boobies in flight, accompanying Dawn 2 ferry to St. Maarten. Photo credit: © Kai Wulf

Population Counts

Between 2008 and 2010, a population count study was conducted in this area by STINAPA Bonaire and a group of 17 citizen scientists (trained volunteers) to provide an estimated number of Brown Boobies roosting along the northwestern coast of Bonaire as well as to note any other roosting seabirds or banded birds in the area. In addition, this study worked to increase awareness of these seabirds among reserve staff, local residents and visitors involved in the monitoring program.

The numbers provided were the first update in over 50 years. During the study, 7 cliffside sites were selected between Malmok and Playa Funchi, areas known to be regularly visited by roosting seabirds. Seabirds in these areas could only enter and exit the roosts by flying in from the sea, so monitoring consisted of taking an initial count, then adding or subtracting birds as they flew in or out over the course of an hour.

The Results

During the study, the largest number of Brown Boobies counted was in July 2009, with 240. Throughout the study they saw no evidence of breeding nor any banded birds, however a few other roosting birds such as Masked Boobies (Sula dactylatra) and Brown Noddies (Anous stolidus) were documented. Another interesting trend was that the highest number of Brown Boobies were counted in July of each year, and a minimum number occurring in January. Although the numbers for the Brown Boobies were lower in 2009 than in 2010, this data suggests that the overall numbers may be on the rise. This is most likely attributed to establishing and managing the protected area around these roosting sites.

Overall, there is still a lack of information concerning these important seabirds. Further information on the breeding grounds for these species could help researchers understand changes in population dynamics. Additionally, a color banded tagging technique would be useful for tracking particular birds without requiring the birds to be physically captured to read the tag. This study provided the first official update in nearly half a century concerning these iconic seabirds. Understanding changes in local seabird populations can allow conservationists and policy makers to create effectively manage plans for these species into the future.

A map showing the seven selected sites between Malmok and Playa Funchi along the northwestern coast of Bonaire. Map credit: Alison Olivierre

Report your sightings

Please report any sightings or photos you have of Brown Boobies, or any other seabird species on https://dutchcaribbean.observation.org. This is a free website and app (iPhone (iObs) & Android (ObsMapp) which allows local citizens to report sightings of important plants and animals. These tools are available in over 40 languages and can be used by biologists and citizens and tourists alike. Species reports by local communities are invaluable for nature conservation efforts to help increase public awareness and overall species protection. Besides, Observation.org is working together with Naturalis Biodiversity Center on automated species identification software. Your uploaded photos are of great value to make this possible. For questions, please contact research@DCNAnature.org