One year after Desecheo Island, Puerto Rico was declared free of invasive species, Island Conservation and partners are beginning to see signs of recovery, including Audubon’s Shearwaters sighted on the island for the first time and new Bridled Tern nests discovered.
Historians say that you could hardly see the sky for the birds. This was once upon a time on Desecheo Island, a National Wildlife Refuge managed by the U.S. Fish and Wildlife Service (FWS) off the shores of Puerto Rico. The island was previously a major nesting area for thousands of seabirds and was so teeming with life that a perpetual “black cloud” of birds hovered overhead the mountainous terrain. So, what caused that clamorous, lively island atmosphere to fade into calm and quiet?
The island was exposed to non-native, damaging (invasive) species in the early 1900s. Feral goats, feral cats, and rats were brought in or floated in on ships and boats and began to alter Desecheo’s ecosystem. Rhesus macaques were brought to the island in the 1970s. Invasive species alone are enough to drive species to extinction and trigger ecosystem collapse. Combined with poaching and egg harvesting by people, as well as military activity, the pressure from invasive species was too much for the fine-tuned, evolutionarily precise ecosystem of Desecheo Island. Little by little, native birds began to disappear from their compromised home. Maybe some birds found other nesting sites—certainly many were lost to predation.
Now it was extinction, not a big bustling cloud of birds that was looming over the island.
Conservation Turns the Tide
A mammoth project to remove the invasive predators was carried out over ten years by multiple conservation groups and agencies. A significant undertaking to remove rats from the island, by the FWS, Island Conservation, and other partners came to fruition in 2017. The project’s success was monumental, making headlines and inspiring celebration. Everybody was excited, hoping to watch the recovery of breeding populations of the ecosystem, including its native large‐bodied seabirds (i.e. Brown Booby, Red‐footed Booby, Magnificent Frigatebird, and possibly the White‐tailed Tropicbird), as well as small‐bodied seabird species (i.e. Bridled Tern and Brown Noddy).
Soon after the project’s completion, the remembered storm cloud of seabirds was suddenly displaced by the real storm clouds of hurricane Maria. Despite notable damage to the island’s environment, the ecosystem continued to show signs of recovery. Soon, the region’s endemic (found nowhere else on earth), Federally Threatened Higo Chumbo cactus, free from the damages of invasive species, was surging back.
But, what about the birds?
Birds sometimes or oftentimes need additional encouragement to come back to a once life-threatening place. Luckily, some dedicated conservationists were scheming up a plan for the seabirds. In February 2018, Island Conservation, FWS, and Effective Environmental Restoration (EER) initiated a seabird “social attraction” project to encourage birds to return to the island.
So how exactly do you invite seabirds back to an island they have learned to avoid? Humans already know this one well: you create the impression that others are already there having a good time. Social attraction involves placing visual cues such as decoys—that is, hand-crafted seabird models—and audio recordings of birdcalls in the habitat. Decoys and recordings have proven successful in the past, supporting the establishment of colonies in places where they’ve not been seen for years.
The partners set out to specifically encourage Bridled Terns (Onychoprion anaethetus), Audubon’s Shearwaters (Puffinus lherminieri), and Brown Noddies (Anous stolidus) to return to Desecheo Island. Audubon’s Shearwaters are quaint birds with pale undersides and dusky grey wings. They love to nest in rock crevices, though sometimes dig their own burrows. Squid and crustaceans are at the top of their menu. Bridled Terns have a narrow build and a sharp silhouette, along with distinctive orca-like patterns on their faces and bodies. Like the shearwaters, these petite birds, as well as the Brown Noddies, have a taste for squid. Brown Noddies nest on rock ledges, the ground, and rarely on vegetation.
Island restoration specialist Cielo Figuerola explained the reasoning behind these choices in bird species for the attraction project:
“Bridled Terns have been observed nesting on Desecheo for decades but in low numbers. We wanted to increase the number of breeding pairs and also the breeding areas around the island. It has been shown that tern decoys are very successful in attracting tern species, and more so, it is more likely that other seabird species will consider visiting the island again once tern colonies are actively utilizing this habitat – so terns are a great species to start a social attraction project with. As for the Audubon’s Shearwater, although there were no records of this species inhabiting Desecheo Island, the nesting habitat on the island is ideal for this species, with many crevices and burrows along the rocky coast. The species visits nearby islands so we know it is around, it is just a matter of setting up the right scenario on Desecheo for it to visit it as well. These shearwaters are very vulnerable and sensitive to invasive species impacts and presence, so it is very unlikely you will find nests on islands currently with the presence of these predators. Now that Desecheo Island is free of invasive predators, it becomes a perfect place for the shearwaters to visit and nest.”
EER placed decoys and sound systems to attract Brown Noddies. Noddies have been observed on Desecheo before, and nests have been documented, but in very low numbers, so EER is looking to attract more individuals and eventually increase the numbers of the Brown Noddies on the island. Seabirds play important roles in island ecosystems—having them present is beneficial to plants and wildlife not only on the island but also in its surrounding waters.
Figuerola explains the social attraction strategy that she and partners deployed:
For the terns we placed decoys on an area suitable for them to start establishing a colony but where this species had not been observed in years. For the shearwater, we placed solar-powered sound systems with speakers to play back their distinctive breeding call during the night. We placed trail cameras in all the sites to document any seabird activity nearby. Setting up the solar-powered sound systems, the speakers and the decoys, and other equipment pieces was no easy task; we had to carry very heavy batteries and bulky backpacks along steep hills and cliffs. However, all these efforts were worth it.
In June 2018, the team visited the island once again to search for birds, check on the status of the sound systems, collect memory cards, and switch batteries from trail cameras. Checking trail cameras for footage is a time-consuming and tedious task. Imagine clicking through thousands of images in search of just one thing. Each click, however, offers a tiny possibility of a great thrill—and the team was lucky to experience just that. When they checked the photos from the trail cameras they found the kind of footage that only a conservationist working to prevent extinctions on a remote island can truly appreciate: an Audubon’s Shearwater standing on top of one of the speakers. Figuerola exclaimed:
We were so excited by this—it marked the first time ever that an Audubon’s Shearwater was recorded on Desecheo Island! This finding is very important because it demonstrates that social attraction with seabirds works; the appearance of the Shearwater on the speaker will inform future conservation management decisions, on Desecheo and undoubtedly other island ecosystems!
There was more good news still to come. When visiting the Bridled Tern decoy colony, the team found two certain and one suspected Bridled Tern nests in an area that Bridled Terns had never before been observed to be present. While Brown Noddies were not observed nesting in the area where decoys, mirrors, and recordings were placed, EER will continue to monitor the island to search for new individuals and nests.
EER, in cooperation with FWS, continues to conduct biosecurity monitoring and check cameras, chew tags, and traps for any possible evidence of reinvasion by invasive species. After more than a decade of efforts to remove invasive species, these conservationists will do everything they can to uphold the important work that has been accomplished.
Figuerola’s excitement and optimism were palpable. She foreshadowed a promising future:
Our next step is to go back to the island in the following months to look for Audubon’s Shearwater nests, conduct further seabird monitoring, and check again on the sound systems and decoy colony on island. It is exciting and rewarding to think about how all of these seabird species are making a comeback to the island, and we are hopeful that one day in the not-too-distant future, we’ll have an island full of activity.
With continued support, the project is expected to make important strides in ecosystem recovery. Thanks to the efforts of conservationists and the supporters that make island restoration possible, there is a chance that one day, looking upward from the scrubby slopes rising from the sea, you will hardly be able to see the sky for the birds—as it once was on Desecheo Island.
Featured photo: Bridled Tern egg on Desecheo Island in 2010. Credit: UCSC/Island Conservation
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