Variation in Breeding Burrows of Streaked Shearwaters Breeding in Sasu Island, and Predation Rates by Norway Rats

Abstract

The seabird plays an important role as one of the indicator species for the status of and changes within marine ecosystems. Therefore, the conservation of seabirds and their habitats is important for maintaining the structure and function of marine ecosystems. Biological invasions affect most ecosystems on oceanic islands. In particular, Rattus spp. is the invasive species with the greatest impact on the seabird population. Introduced predators, like rats, severely affect seabirds and endanger them worldwide. The breeding population of Streaked Shearwaters Calonectris leucomelas in Sasu Island is one of biggest seabird colonies in Korea, and the Norway Rat Rattus norvegicus is known as an alien predator in this island. In this study we investigated rates of burrow occupancy and breeding success of Streaked Shearwaters for 7 years, and the impact of Norway Rats on the breeding success of Streaked Shearwaters breeding in Sasu Island for 4 years. Our results show that the percentage of breeding burrows decreased according to breeding stage during several years in the monitoring period, and that predation by the Norway Rat was the main cause in hatching failures. Consequently, although our results indicate that their breeding population is not likely to decline, Norway Rats have been affecting the breeding status of Streaked Shearwaters on Sasu Island during the last decade.

Invasive species and Pacific island bird conservation: a selective review of recent research featuring case studies of Swinhoe’s storm petrel and the Okinawa and Guam rail

“…Invasive vertebrates (e.g., rats, cats, dogs, pigs, goats, mice, snakes) have been well documented as causes of population declines in seabirds breeding on islands (Veitch et al 2011). For example, predation by Norway rats contributed to a hatching failure rate of 81-89 % in a breeding colony of *7000 pairs of streaked shearwaters (Calonectris leucomelas) on Sasu Islet in the Republic of Korea (Nam et al 2014). By contrast, non-vertebrate invasive species, and particularly invasive plant species, interactions with native island birds have been less studied and are poorly understood (Meyer 2014).…”