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12 March 2025 - Case studies
Invasive alien species introduced by humans to islands can have devastating impacts on local ecosystems and native species—often far greater than the damage they cause on the mainland.
Island ecosystems are especially vulnerable to invasive species for two main reasons. First, alien species arriving on islands often encounter no natural enemies or predators to regulate their population. Second, island-native species have typically not evolved defenses against such newcomers, due to the historical absence of predators in their environment. As a result, the introduction of a new species—whether accidental or intentional—can disrupt a fragile ecological balance.
The threat to endemic island species is very real. Islands often host unique species found nowhere else on Earth. Once these species go extinct locally, they are lost forever.
The black rat (Rattus rattus) and the brown rat (Rattus norvegicus), both originally from Asia, have spread worldwide due to human activity. Numerous studies highlight their harmful effects on island ecosystems, where they damage native species and habitats. This issue is especially evident in the Mediterranean, where the black rat is the most widespread mammal on islands. It preys on seabirds—particularly Scopoli’s shearwater, Manx shearwater, and storm petrels—feeding on eggs, chicks, and in some cases, even adults.
One striking example is Foradada Island off the coast of Sardinia, where one of the last Italian colonies of storm petrels survived thanks to a cave almost inaccessible to rats. Unfortunately, in 2023, a rat—likely having swum to the site—reached the cave, devastating the colony and killing many adults and chicks.
Picture: Pulcino di berta maggiore – Image credits: Ferdinando Corbi
To mitigate the destructive effects of rat predation, island-wide eradication is possible and has shown positive results. In the Mediterranean, black rats have been successfully removed from several islands, including Montecristo, Tavolara, Giannutri, Zannone, and Pianosa. These actions have led to the recovery of seabird breeding populations and the restoration of ecosystem functions.
Eradicating rats from inhabited islands also offers substantial benefits to local communities. A prime example is Ventotene, home to around 700 residents, where between 2018 and 2021 a black rat eradication project was carried out. Coordinated by the Lazio Region and funded by the EU LIFE Programme, the initiative significantly reduced the costs of rat management, damage caused by rats, and the annual use of rodenticides by residents. It also eliminated vectors of pathogens such as toxoplasmosis and leishmaniasis.
In January 2020, Scopoli’s shearwater chicks—a species once threatened by black rats on the island—began flying again, marking a significant conservation success.
In January 2020, Scopoli’s shearwater chicks—a species once threatened by black rats on the island—began flying again, marking a significant conservation success.
Today, Ventotene is the most populated rat-free island in the world, serving as a model for similar projects in the Mediterranean and beyond.
Bell Labs, aware of the damage caused by rats and other human-introduced species on islands, has participated in over 100 environmental conservation projects focused on the eradication of invasive rats and mice and the restoration of island ecosystems.
A notable example is Floreana Island in the Galápagos, where introduced rats and mice devastated local ecosystems by preying on bird eggs, lizards, and turtles, and consuming native plants used for food and shelter. With an area of nearly 67 square miles, the eradication project represented a significant challenge.
The Floreana Project involved collaboration with the local community, the distribution of necessary materials, and the development of bait formulas suited to tropical climates, effective in both wet and dry conditions. After years of planning, the project officially launched in October 2023, aiming to protect endangered species by removing invasive rodents from the island.
Another major success story in recent decades is the eradication of Norway rats from 65 islands in the Falkland Islands archipelago. Starting in 2001, local teams were led by New Zealand expert Derek Brown, whose expertise was vital to the success of many of the rat eradication efforts.
The main method used was manual bait distribution. Pre- and post-eradication surveys associated with each project showed significant increases in bird populations following the removal of Norway rats.
Although in parts of the Falklands, rats have been observed swimming up to 800 meters—and in some cases colonizing islands up to 1.3 km offshore—this distance is now considered the minimum “safe” buffer zone when evaluating the feasibility of rat eradication in the Falklands.