Italy eradicated black rats from Zannone in 2007; nine years later, Scopoli's shearwater nesting pairs had nearly tripled from 27 to 80 on the Mediterranean island

Imagine a 1.5-square-mile volcanic rock in the middle of a swimming reef, somewhere between the imagination of a scuba diver and a nesting seabird. Zannone is one of the Pontine Islands near Rome, and for many years it had an unwelcome extra resident: black rats (Rattus rattus), long-time ship stowaways and general pests in the local ecological balance. But in 2007, conservationists removed the offending rodents, and as a result, the island's Scopoli's shearwaters, burrow-nesting seabirds that are vulnerable to the omnivorous predators, have since flourished. Their number jumped from 27 breeding pairs to 80 around the time of the reporting, a rise the 2017 study titled “Island invasives: scaling up to meet the challenge,” by Capizzi et al., in the IUCN's Proceedings of the International Conference on Island Invasives, linked directly to the rat removal.

Why one invader stands out from the pack

Shearwaters and their close relatives, the petrels, are textbook cases of insular endemics: birds which have adapted to the particular ecological niche of a given region, frequently an island, and suffered greatly when the introduction of foreign species contributed to their decline. They also happened to be particularly vulnerable to one such invader: the black rat.

A 2008 global review titled “Severity of the Effects of Invasive Rats on Seabirds: A Global Review,” by Jones et al., in the journal Conservation Biology, compiled data from 94 different studies concerning 75 species of seabirds across 61 islands and found that rats were responsible for significantly sharper declines among burrow-nesting seabirds compared to other introduced predators. And within the rats themselves, the black rat stood out as exceptionally harmful.

An issue that goes well beyond Italy

It's understandable why such a discovery would resonate so strongly with the scientists and conservationists who live in the region and have the most direct connection to the local ecology, but the problem is by no means confined to one country or even one continent. Rats reached the Aleutian Islands as early as the 1780s, when they swam ashore from Japanese shipwrecks, becoming so entrenched on one island that it was later named "Rat Island." That same long-running invasion is the backdrop for a 2008 paper titled “Introduced rats indirectly change marine rocky intertidal communities from algae- to invertebrate-dominated,” by Kurle, Croll, and Tershy, published in the Proceedings of the National Academy of Sciences, which found that the rodents not only decimated the local seabird populations of the Aleutian Islands, but affected the coastal food webs as well, with an indirect effect on populations of shorebirds, invertebrates, and algae.

What makes a good conservation success story?

Conservation success stories of this sort rarely make for flashy headlines, even when the on-the-ground work behind them is anything but tame. The method by which the rodents were removed from Zannone was not pretty; the use of helicopters to drop poisoned baits among the rocky terrain was potentially hazardous to both the wildlife and the conservation workers who had to trek through it. That demanding fieldwork is also why ongoing biosecurity monitoring matters: the 2007 eradication itself is complete, but the shearwaters' recovery depends on keeping the island rat-free. If rats are ever reintroduced, say, by a passing ship, the population could rebound quickly, undoing nearly a decade of gains.

Few conservation agencies tend to have a vested interest in emphasizing the value of projects like this, since they're usually looking for funding, and any given campaign has only so many high-profile angles it can use before it starts to feel cheap and desperate. The reality, in brief, is that the increase in the number of Scopoli's shearwaters on Zannone is one completed victory within a much larger, still-ongoing field of island conservation work worldwide, one that depends on continued vigilance, even where individual projects like this one have already succeeded. It is nonetheless a crucial piece in the larger puzzle of conservation science.