Feral cats pose a threat to rare seabird populations on the Sister Islands, according to researchers who worked on a two-year study of nesting colonies.
The numbers of red-footed booby birds on Little Cayman and brown boobies on the Brac are declining, according to Jane Haakonsson, a researcher with the Department of Environment’s terrestrial resources unit.
The department partnered with the National Trust and seabird experts from the Universities of Liverpool and Exeter in the study, which was largely funded by the U.K.’s Darwin Initiative, a grant scheme for projects aimed at protecting biodiversity.
Researchers tagged and tracked the movements of three types of seabirds on the Sister Islands, monitoring population numbers and mapping foraging routes.
Ms. Haakonsson said that while magnificent frigate bird populations were relatively stable, the numbers of both types of boobies appeared to be declining.
“We are seeing a negative population trend,” she said. “One of the biggest pressures we discovered comes from feral cat predation – we lost five adult breeding birds on a single weekend in the Brac last month, which is a high percentage because the population is quite small.”
The Department of Environment had planned to partner with the Department of Agriculture for a cull of feral cats on the Sister Islands, but that project has been postponed amid a legal challenge from animal welfare groups who are calling for a more humane approach to the problem.
According to the initial finding of the seabird study, there are fewer than 200 brown boobies on the Brac, potentially as few as 120. The red-footed booby colony on Little Cayman numbers around 2,100, while there were 1,300 frigate birds, according to population estimates.
Ms. Haakonsson said researchers had used drones and ground surveys of nests to monitor the birds. The two-year study ended last month and the findings will go toward the publication of scientific papers that will help inform conservation policy.
Birds were tracked during the study using tiny GPS tags attached to their legs to map their movements.
“The three species didn’t really overlap. They had very different foraging strategies, some of which were quite new to science. We have some really interesting publications coming up,” Ms. Haakonsson said.
“Red-footed boobies were leaving for five days at a time and going as far as Negril [in Jamaica]. Brown boobies were foraging more locally.”
Rhiannon Meier, a research associate at the Universities of Liverpool and Exeter and the coordinator of the Cayman seabirds project, said more than 150 tracks had been recovered for brown boobies, 50 from red-footed boobies, and around 100 from frigate birds. All the tracks come from adult birds tagged during the chick rearing period. Additional tagging and tracking work is being done for immature frigate birds.
She said the data showed distinct habits associated with each species.
Brown boobies stay close to their nesting sites on the Brac, usually making trips shorter than 12 hours and never going beyond 44 miles from the colony.
Red-footed boobies, based around a colony in Booby Pond, Little Cayman, traveled as far as 186 miles from their nests and were gone for days at a time. Frigate birds, which are much larger, traveled up to 560 miles from the islands, making trips that varied from a few hours up to 12 days to forage for food.
Ms. Meier said the research was vital because the seabird populations on the Sister Islands were significant.
“The red-footed booby population is considered internationally important and is one of the largest in the Caribbean, and both the frigate bird and brown booby populations are regionally important in terms of size,” she added.