NT
Swinhoe's Storm-petrel Hydrobates monorhis



Justification

Justification of Red List Category
This species is listed as Near Threatened on the basis that its population is expected to undergo a moderately rapid decline over the next three generations, owing to the impacts of introduced species and human activities, such as mining and tourism.

Population justification
Brooke (2004) estimated the global population to number c.100,000 individuals, which roughly equates to 66,666 mature individuals. Based on Boersma and Groom (1993) and Birdlife International (2009) estimates, Sato et al. (2010) describes the world population at a minimum of 130,000 pairs, which equates to 260,000 mature individuals. The population is therefore estimated at 66,666 - 260,000 mature individuals, rounded here to 65,000 - 260,000 mature individuals.

Trend justification
The population is expected to undergo a moderately rapid decline over the next three generations, owing primarily to the impact of introduced species.

Distribution and population

Hydrobates monorhis breeds on Verkhovsky Island (7,500 pairs), south of Vladivostok, Russia, and Japan (a minimum of 1,000 pairs). There are little-known populations in China, Chinese Taiwan, North Korea and South Korea, and records suggest that breeding possibly occurs in the North Atlantic (Silva et al. 2016). In winter, it migrates south and west to the northern Indian Ocean (Brooke 2004). Based on Boersma and Groom (1993) and Birdlife International (2009) estimates, Sato et al. (2010) describes the world population at a minimum of 130,000 pairs, confirming that the species has a very large population. However, Birds Korea (2010) state that c.100,000 pairs nest on Gugeul Islet, implying that possibly over 75% of the global population breed on one very small island. The species nests at six or seven breeding islets in South Korea (Chang-Yong Choi in litt. 2012).

Ecology

This marine species can be found over pelagic and inshore waters. Its feeds mainly on the wing by dipping and does not patter. Breeding starts in April forming loose colonies on offshore islands in burrows (del Hoyo et al. 1992).

Threats

Swinhoe’s Storm-petrel is threatened by a number of invasive species. The colony on Koyashima Islet, Fukuoka, experienced dramatic population declines in response to the accidental introduction of Brown Rats Rattus norvegicus (Sato et al. 2010). Despite an eradication effort rats were found to be present on the islet again by 2009 and the colony was close to extirpation by 2012 (Pacific Seabird Groups and Japan Seabird Group 2014). The seeds of the invasive Oriental Chaff Flower Achyranthes japonica represent an entrapment risk. The plant has established in all the main breeding colonies in Korea, which represent over 90% of the world’s breeding population of Swinhoe’s Storm-petrel (Lee et al. 2012). In October 2009, at least 386 Swinhoe’s Storm-petrels were recorded to have been killed by entanglement with A. japonica, 88% of which were adults (Arcilla et al. 2015). Due to the small clutch sizes, long lifespan and low natural adult mortality, even a small increase in adult mortality represents a significant threat to the population (Arcilla et al. 2015). Invasive Mugwort Artemisia vulgaris also occurs across much of Swinhoe’s Storm-petrel’s range. An increase in alien plant cover has been shown to reduce the breeding density of Swinhoe’s Storm-petrel (Lee and Won 1988, Arcilla et al. 2015). There have been successful mitigation efforts by physical removal of invasive plants (Arcilla et al. 2015).

There has been a considerable decrease in the population of Swinhoe’s Storm-petrel at a number of historical breeding sites in Japan, in some cases extending to a complete absence of active breeding populations. Breeding is believed to have ceased on Bentenjima Islet in Shiriyazaki, Aomori Prefecture, after it was connected to the mainland for the mining of limestone, as well as a number of other islets with less obvious disturbances (Sato et al. 2010). A number of colonies are threatened by human disturbance, with the breeding population on Verkhovsky Island threatened by recreational users in warm seasons (Sato et al. 2010).

Competition with closely related species is known in some areas of Swinhoe’s Storm-petrel’s range. On Hide-Shima Island, Iwate Prefecture, competition with Madeiran Storm-Petrels and Streaked Shearwaters has been reported. However, competition only occurs in areas with nesting conditions suitable for the competitor species (Sato et al. 2010).

Swinhoe’s Storm-petrels have been measured to have tissue lead concentrations above the toxic threshold level for avian species (Beyer et al. 1996). This may be due to anthropogenic lead contamination as well as exposure to natural lead, although there is little evidence to substantiate this claim, nor evidence for an impact at the population level (Lee et al. 2012).

Conservation actions

Conservation Actions Underway
The main colonies in South Korea are already dependent on active conservation measures, including the eradication of invasive alien species and prevention of disturbance (N. Moores in litt. 2011). The main breeding colony on Verkhovsky Island has been protected since 1984 which has stopped disturbance of nests by tourists.

Conservation Actions Proposed
Carry out regular surveys to monitor population trends. Implement measures to control invasive species at as many affected colonies as possible. Mitigate the impact of tourism at relevant sites. Implement and enforce controls on landings by fishing boats.

Acknowledgements

Text account compilers
Miller, E., Moreno, R., Stuart, A., Symes, A., Taylor, J., Ekstrom, J., Fisher, S., Calvert, R., Butchart, S., Fjagesund, T., Harding, M., Hermes, C., Martin, R.

Contributors
Sato, M., Moores, N., Takeishi, M., Choi, C., Bretagnolle, V., Jayadevan, P.


Recommended citation
BirdLife International (2022) Species factsheet: Hydrobates monorhis. Downloaded from http://www.birdlife.org on 29/06/2022. Recommended citation for factsheets for more than one species: BirdLife International (2022) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 29/06/2022.