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Island’s Invasive Species Wreak Havoc: How Did They Get Here?

Fernando de Noronha is a UNESCO World Heritage Listed site for its natural values, but beneath the tourism and pristine island beaches is a plague of pests threatening to eat everything.

Black rat (Rattus rattus) running along a tree on Fernando de Noronha (Photo by James Russell)
Black rat (Rattus rattus) running along a tree on Fernando de Noronha (Photo by James Russell)

I have spent the past three weeks on the island working with a TRIADE (Brazilian Institute for Conservation Medicine) team researching invasive species on Fernando de Noronha. I have been focusing on the introduced rats (Rattus rattus) in the forest ecosystems (mark National Invasive Species Awareness Week).

After six nights mark-recapture trapping at our study site we have estimated their density at a staggering 27 per hectare. This is after the population crash at the end of the dry season, and in the presence of cats which roam freely around the island preying on rodents but also native birds such as the white-tailed tropic bird (Phaethon lepturus). It always amazes me that an island can be granted World Heritage status before a simple and necessary task such as eradicating all the cats and rats has first been undertaken. Should this be a condition for World Heritage status?

A white-tailed tropic bird killed by a feral cat on its nest at Fernando de Noronha
The sight of a white-tailed tropic bird killed by a feral cat on its nest is not uncommon at Fernando de Noronha. (Photo by James Russell)

Tatiane Micheletti is a doctoral student from the Technical University of Dresden in Germany and has been studying the rock cavy (Kerodon rupestris), or mocó as it’s known locally. This Brazilian rodent is native to the dry north-eastern areas of the continent but was introduced to Fernando de Noronha in the 1960s as hunting sport for the Brazilian military. Since then it has colonised the entire island, and is found on rocky cliffs and banks throughout, feeding on bark and leaves. In some ways, it might resemble the Vespucci’s rat (Noronhomys vespuccii) long since extinct on the island.

Tatiane Micheletti studies an anaesthetised mocó in the ICMBio laboratory with the assistance of intern Vini Gasparotto
Tatiane Micheletti studies an anaesthetised mocó in the ICMBio laboratory with the assistance of intern Vini Gasparotto. (Photo by James Russell)

Meanwhile, Carlos Abrahão from ICMBio is about to start a doctorate at the University of São Paulo studying the tegu (Tupinambis merianae). This three-foot Brazilian lizard is also native to the continent and was also introduced to the island in the 1960s. This was a dismal attempt to control mice doomed from the start because tegu are only active in the heat of the day while mice are only active in the middle of the night. Today tegu roam across the island preying on turtle nests, the endemic mabuya (Trachylepis atlantica) and worm lizard (Amphisbaenia ridleyi) and anything else they can find.

Carlos Abrahão sets a trap in the forest to catch rats and tegu
Carlos Abrahão sets a trap in the forest to catch rats and tegu. (Photo by James Russell)

The relationships among all these introduced species are complex. Cats and tegu are the top predators in the ecosystem, likely in competition with one another, though active at different times of the day. Rats and mocó also impact animals and plants respectively in the ecosystem, while providing an alternative prey source to cats and tegu. It will take a few more years of study and visits to Fernando de Noronha before we can completely unravel the relationships and propose the best management strategy to the island administrators for all these introduced species.

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