Feral Cats Prey on Endangered Streaked Shearwater Population on Mikurajima Island

The streaked shearwater, a seabird identified as near threatened by the International Union for Conservation of Nature (IUCN), is severely impacted by feral cats on Mikurajima Island in the Izu Islands. Recent research indicates that more than 30,000 of these birds are killed annually due to predation by cats, with the study conducted by a team that included the Forestry and Forest Products Research Institute. The island, which lies approximately 200 kilometers south of Tokyo, boasts the largest breeding population of streaked shearwaters in the world.

In the late 1970s, the shearwater population was estimated at over 1.75 million, but alarming declines were noted by 2016, when numbers dropped to roughly 100,000. Consequently, the IUCN classified the streaked shearwater as near threatened in 2018. The research team highlighted that the birds have low vigilance, making them an easy target for the feral cats, whose exact impact was previously unknown.

During a study conducted from January to March of the previous year, researchers examined cat feces to assess the impact of these predators on shearwater populations. They found that each feral cat was estimated to kill around 330 shearwaters per year. Given that 106 feral cats were trapped in the area during fiscal 2022, the researchers deduced that the annual predation rate exceeds 34,980 birds, prompting calls for the national and Tokyo metropolitan governments to implement stronger control measures to safeguard these vulnerable seabirds.