The history of anthropogenic disturbance and invasive alien species impact on the indigenous avifauna of the Ogasawara Islands, southern Japan

Abstract

The Ogasawara Islands are subtropical oceanic islands in the Northwestern Pacific. Since their unique ecosystem is recognized to have outstanding universal value, they are registered as a UNESCO World Natural Heritage site. However, human settlement since 1830 has seriously impacted the biota. So far, the breeding of 20 land birds and 21 seabirds, including three introduced species, has been recorded on the islands. Seven endemic species/subspecies have become extinct, and breeding populations of five species have disappeared completely. Such extinctions have been caused by habitat loss, overhunting, and alien species invasion. Specifically, alien mammals are thought to have had devastating effects on avian populations. At least ten mammal species have been introduced, five of which (goats, cats, black rats, Norway rats, and house mice) still occur there today. Owing to their serious ecological impacts, eradication programs have been implemented. Feral goats had spread to 20 islands, but have been completely eradicated from all except Chichijima. Feral cats currently exist on only four islands and are being removed from natural areas on Chichijima. Non-native rodents have invaded almost all of the islands. Eradication programs using rodenticide are ongoing on some of the islands and have succeeded on four of them. After successful eradication, some land birds and seabirds have increased in numbers and expanded their distribution. However, undesired results also have been confirmed. For example, invasive plants have increased following goat eradication due to the elimination of grazing, and increasing seabirds have become dispersers of alien plants with adhesive seeds. Rat populations have likely increased after cat eradication due to their release from predation. These accumulated experiences should inform future adaptive management of the islands based on scientific evidence of specific species interactions.

Cryptic Speciation of the Oriental Greenfinch Chloris sinica on Oceanic Islands

“…The Ogasawara Islands originated as a result of volcanic activity approximately 48 MYA and appeared above sea level during the Eocene epoch (Umino et al, 2016). Therefore, it is difficult to know when these islands were colonized by different bird species, with the exception of those species that have only appeared there for a few decades, such as the common moorhen Gallinula chloropus, the bull-headed shrike Lanius bucephalus, and the scaly thrush Zoothera dauma (Kawakami, 2019). Nakamura (2002) suggested that the Ogasawara Oriental greenfinch population originated as the result of an accidental invasion from a northern population located in Kamchatka, the Kuril Islands, or Hokkaido.…”

“…The black rat Rattus rattus, is not found within the breeding range of the Ogasawara greenfinch. This is fortunate, because populations of finches would be unable to survive on islands inhabited by the black rat (Kawakami, 2019). Predation by the black rat is probably the major factor in the local extinction of finch populations.…”

“…Predation by the black rat is probably the major factor in the local extinction of finch populations. The Norway rat, R. norvegicus, has invaded the satellite islands of Hahajima Island and likely preys on finch nests (Kawakami, 2019). Another threat to the finches is predation by the domestic cat, Felis catus, finch feathers have been found in cat droppings at Hahajima Island during non-breeding season (Kawakami and Higuchi, 2002).…”

“…Finches frequently nest in these trees and feed on their seeds (Nakamura, 1997;Kanto Regional Forest Office, 2009). However, C. equisetifolia has been eradicated from the Ogasawara Islands because it forms dense monospecific stands and reduces biodiversity (Kawakami, 2019).…”

Tourist intentions to donate to non-lethal feral cat management at a potential natural World Heritage site in Japan

“…On the Ogasawara Islands and Teuri Island, adoption programs have effectively reduced the number of feral cats with the estimated population now under 10 on Chichi-Jima Island, which is one of the Ogasawara Islands (Tokyo Veterinary Medical Association, 2016), and the number has been reduced from 143 to closely zero on Teuri Island (Haboro City, 2019). As a result, the populations of endemic species, such as seabirds, have recovered on these islands (Kawakami, 2019).…”