After invasive rodents were cleared from Surprise Island in 2005, three monitored seabird populations grew two to tenfold in the years that followed

Picture a speck of land, isolated in the South Pacific by a 125-mile radius, without wifi or coffee shops but with plenty of coral sand, scrubby bushes, and, until fairly recently, thousands of rats brought in on a ship. That is Surprise Island, part of New Caledonia's d'Entrecasteaux Reefs, which sounds like the setting for a nature documentary; instead, it ended up as one of the most realistic field tests for both the effectiveness of people cleaning up a mess and staying long enough afterwards to see if it really was.

In 2005, conservation groups eliminated Surprise Island's invasive rats. What happened next is more interesting: the scientists who did it waited around for sixteen years to see if the seabirds who used to nest safely there would return. According to ecologist Martin Philippe-Lesaffre and his colleagues' long-term 2023 study titled “Recovery of insular seabird populations years after rodent eradication,” published in the journal Conservation Biology, three seabird species on Surprise Island saw their breeding populations grow between two and ten times larger in the years following the eradication. That's the kind of hard, multi-year evidence conservation science doesn't get often enough: proof, gathered over more than a decade, that an intervention actually worked, not just a feel-good story.

The island time forgot, then fixed


Surprise Island is small (about 24 hectares of sand and low vegetation) and uninhabited except for the wildlife that nests there. Ship rats had invaded it at some time in the past, as they have done on islands over the world, and were preying on seabird eggs and chicks. In 2005, a rodent eradication campaign succeeded in getting rid of them, and researchers confirmed the island was rat-free the next year.

What makes this success more than a neat field study is patience. Researchers surveyed the island's seven seabird species every year for four years before and four years after the eradication, and then went back for single surveys roughly ten years and then about fifteen years after the event. That's not typical in conservation science, where interest often dries up long before the ecosystem has had time to fully assimilate any changes.

The numbers that made biologists sit up

According to the same 2023 study, not every species responded so well or quickly, but that's part of what makes these results interesting. Three of the seven species surveyed had population gains, with breeding pairs increasing two to tenfold compared to before the eradication. Two of the species: noddies and frigatebirds, saw increases fairly shortly (within about four years), which the researchers attribute to birds immigrating from nearby islands, since Surprise Island's seabirds tend to stay loyal to a breeding site, but a newly rat-free Surprise became an attractive place to settle once the threat to eggs and chicks was gone. A third species: the red-footed booby, took much longer to respond, waiting at least five years before numbers started to climb and then continued to increase for over a decade afterwards. That's a longer period than a short three- or four-year survey might pick up, and it could easily have missed this last wave of recovery, concluding that the eradication hadn't helped this particular species.

Why a tiny Pacific atoll should matter to Americans

This study isn't just a curiosity for seabird enthusiasts. According to a separate 2007 widely-cited review titled “Invasive Rodent Eradication on Islands,” also published in Conservation Biology, performed by Gregg Howald and his colleagues, rodent eradication has been attempted on hundreds of islands around the world by that point, with a success rate above 90 percent: 332 successful eradications against 35 failures. Native species that were accidentally hurt in the process generally bounced back toward their original levels of abundance.

In other words, this isn't an innovative fringe idea. It is a conservation tool with documented success, and Americans don't have to look far to see it in action: back in 2001 and 2002, teams eliminated black rats from Anacapa Island, part of Channel Islands National Park on the Southern California coast, and afterwards saw significant increases in seabird nesting over the following decade.

A similar story comes from the other side of the world. In a 2024 research paper titled “Long-term monitoring highlights the positive responses of the seabird community to rat eradication at Tromelin Island, Western Indian Ocean,” published in the journal Conservation Science and Practice, researchers found that by 2022, seventeen years after rats were eradicated from Tromelin Island in 2005, five seabird species had successfully re-established themselves there, with some seeing population gains within just a few years. Again and again, it seems that eliminating an invasive predator lets the birds get back to business.

A few caveats before anyone celebrates too hard

None of this makes rodent eradication a magic solution, and it's worth holding that alongside the strong track record above rather than against it. Not every species responded positively, and the Surprise Island researchers themselves note that some populations did not grow significantly. The Howald review also acknowledges that these campaigns typically involve rodenticides, which can hurt other animal species during the campaign, even if these populations usually bounce right back.

Plus, as the timeline drawn from Surprise Island shows, patience is vital in conservation; it's easy to conclude that an eradication campaign has failed prematurely (especially if the grant runs out too soon) if people don't wait until the slower species have had time to recover. But on the whole, it's fair to say that eliminating an invasive predator gives conservationists room to breathe, and that's something conservation groups could probably use more of in the years ahead.