National Geographic

GOUGH ISLAND, a 25-square-mile mass of vol-canic rock in the South Atlantic Ocean, is hometo millions of breeding seabirds, including theentire world population of the Atlantic petreland all but a few pairs of the critically endan-gered Tristan albatross. Ross Wanless first wentto Gough in 2003, as a doctoral candidate, afterother researchers had reported that alarminglyfew petrels and albatrosses were fledging chicks.It was known that rats and cats, which humanshave introduced on islands all over the world,prey heavily on seabirds. But there were no ratsor cats on Gough, only mice. Using video camerasand infrared lights, Wanless recorded what themice were doing to the petrel chicks. “The sunwent down,” he said, “and a mouse came out inthe petrel burrow. It hesitated and then startednibbling on the chick. Other mice came, and Iwitnessed this insane, disgusting attack. As theblood started to flow, the mice got more and moreexcited. At times, there were four or five of themcompeting for the wound, lapping up blood andgoing inside to eat the chick’s internal organs.”Having evolved without terrestrial predators,seabirds have no defense against mice. A petrelin its inky-dark burrowcan’t even see what’shappening to its chick,and an albatross on itsnest lacks the instinctto recognize mice as athreat. In 2004, Wan-less noted 1,353 breed-ing failures amongGough’s Tristan alba-trosses, most of themfrom predation, andonly about 500 suc-cesses. In more recentyears, failure has beenas high as 90 percent.Among all seabird spe-cies on Gough, mice now kill two million chicksevery year, and many of these species are alsolosing adults in the fisheries. Annual mortalityamong adult Tristan albatrosses at sea has risento 10 percent—more than triple the rate of naturalmortality. Ten percent adult mortality plus 90 per-cent breeding failure is a formula for extinction.The calamitous decline in seabird populationshas many causes. Overfishing of anchovies andSeabirds area poignantcombination ofvulnerabilityand toughness.An albatrosscan’t stopa mouse fromeating itsyoung.other small prey fish directly deprives penguinsand gannets and cormorants of the energy theyneed to reproduce. Overfishing of tuna, schoolsof which drive smaller fish to the ocean’s surface,can make it more diicult for shearwaters andpetrels to forage. Climate change, which altersocean currents, already appears to be causingbreeding failure among Iceland’s puins, andbirds that nest on low-lying islands are vulnerableto rising sea levels. Plastic pollution, particularlyin the Pacific Ocean, is clogging the guts of sea-birds and leaving them hungry for real food. Andthe resurgence of marine mammal populations—in other respects, an environmental successstory—has resulted in more seals to eat youngpenguins, more sea lions to crowd cormorantsout of their breeding sites, and more whales tocompete with diving birds for prey.The number one threat to seabirds, however,is introduced predators: rats, cats, and miceoverrunning the islands where they breed. Thisis the bad news. The good news is that invasivespecies are a problem with achievable solutions.Organizations such as Island Conservation, anonprofit based in California, have perfected theuse of helicopters and GIS technology to targetpredators with poisoned mammal-specific bait.Animal lovers may grieve at the mass killing ofsmall furry mammals, but human beings have aneven greater responsibility to the species they’vethreatened with extinction, however inadver-tently, by introducing predators.The most ambitious rodent-eradication efortto date was mounted by the South Georgia Heri-tage Trust. South Georgia island, 900 miles fromthe Antarctic Peninsula, is the breeding groundof perhaps 30 million seabirds; without rats andmice, the island could easily host three timesthat number. From 2011 to 2015, at a cost of morethan $10 million, three helicopters traversedevery ice-free area on South Georgia, droppingbait. No living rat or mouse has been detectedon the island since 2015.Similar efforts are now planned for GoughIsland, in 2019, and for South Africa’s MarionIsland in 2020. Mice came to Marion with whal-ers and sealers in the 19th century. In the 1940s,the South African government introduced catsto control them, and the cats quickly went feral.Instead of killing mice, they proceeded to deci-mate the smaller seabird species nesting on theisland. (“Mice know exactly what a cat is,” RossWanless explained. “Seabirds don’t.”) Marion’s136 NATIONAL GEOGRAPHIC