Calling all seabirds: restoring long-lost colonies on Desecheo Island

Lead author Jose Luis Herrera-Giraldo describes his team’s latest study using fake birds and loudspeakers help conservationists restore the long-lost seabird colony of Desecheo Island, Puerto Rico.

For scientists and conservationists, life on Desecheo National Wildlife Refuge in Puerto Rico is harsh with the islands’ rugged terrain, blazing hot sun beating down year-round, and fire ant. But for seabirds the island is paradise – at least, it once was.

Desecheo was historically an important seabird rookery in the Caribbean, with colonies so immense that they blackened the skies above like clouds. My work on Desecheo started in 2009 while surveying an endemic gecko, but I never imagined that would lead to a decade-long effort to bring back the island’s seabird populations.

Seabirds are magnificent creatures—nesting on islands and coastlines worldwide but spending large portions of their lives out at sea, serving as ecological connectors between these ecosystems and delivering essential nutrients. They are also the most threatened group of birds globally, with approximately 30% at risk of extinction; nearly half of all seabird species are threatened by the presence of invasive species (mainly mammals) that devour eggs, chicks, and adults.

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Adult of brown noddy with egg on Desecheo © Island Conservation

For almost 100 years, this was the case on Desecheo, until 2016 when invasive mammals were eradicated, marking a significant conservation achievement for the island and the region. Five years later, the island is showing signs of recovery as plants and native wildlife began to thrive, but seabirds have been slow to return.

Seabirds are social animals and faithful to their nesting sites, meaning they often return to the site where they hatched and only change sites if a population is already established. Since generations had been unable to nest on Desecheo, the memory of the island and the established populations are lost.

Luring back the birds

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Egg and chick of bridled tern on Desecheo © Island Conservation

To bring the seabirds back, Island Conservation, U.S. Fish and Wildlife Service, Effective Environmental Restoration, and The Nature Conservancy devised a plan to trick passing seabirds into thinking there is an existing population, so they will explore and hopefully nest. This is called social attraction, and it’s a well-established seabird restoration practice but has only ever been used on a handful of species.

To start, we identified the seven species of birds known to nest on Desecheo and selected two that had the highest potential success: bridled tern and brown noddy. We also determined that the regionally threatened Audubon’s shearwater would greatly benefit from habitat free from invasive predators, and although they had never been known to nest on Desecheo, records indicate they pass by and potentially visit the island.

Social attraction utilizes a mix of audio and visual cues to draw in passing birds. To bring these birds back to Desecheo, we collected solar-powered loudspeakers, plastic decoy birds, and mirrors – all of which work together to give the appearance of an established colony.

Decoy bridled terns and brown noddies were cemented to the rocky shorelines and interspersed with mirrors, making the colony appear larger than it was. We set up loudspeakers to play looped recordings of the species calls all through the day and night, and finally, we used motion-sensor cameras to see what would happen.

The operation has been underway for three years now, and so far, the outcomes are promising; multiple bridled tern’ adults and nests have been found with eggs and chicks along the south coastline. We have observed between 10 and 20 brown noddy adults perched on rocks and found an egg, but we suspect that more eggs might be around due to the number of adults. As for the Audubon’s shearwater, the first-year cameras captured one individual roosting on top of the speakers on a nightly basis and has since captured a pair potentially mating at the same spot.

These results are positive indicators that Desecheo is on its way to becoming a seabird paradise once again, and in the coming years – with continued social attraction efforts – we hope to see more of these and other species return. As one of the few islands in the Caribbean to be rid of invasive mammals, the restoration of Desecheo and our sustained conservation actions provide a roadmap for similar recovery across the region and globally.

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Jose Luis Herrera-Giraldo with decoys of bridled tern on Desecheo © Island Conservation

Read the full From Practice article: “The use of social attraction techniques to restore seabird colonies on Desecheo Island, Puerto Rico” in Issue 2:2 of Ecological Solutions and Evidence.

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