VU
Leach's Storm-petrel Hydrobates leucorhous



Justification

Justification of Red List Category

Although the trend of western North American and Russian populations are unknown, the compilation of available data collected from 1977 to 2016 representing 75-80% of the global population, points to a decline of ≥30% over three generations. It has therefore been uplisted to Vulnerable. The cause(s) of declines are unknown, but are likely multi-faceted and further research is needed to inform conservation actions.

Population justification
Brooke (2004) estimated the global population to number >20,000,000 individuals.  Based on the compilation of available data the current population comprises 6.7-8.3 million breeding pairs; 40-48% of these breed in the Atlantic basin and 52-60% in the Pacific. Throughout the western Atlantic (>90% of basin total), populations are declining, including at Baccalieu Island, Newfoundland, Canada, home to the largest colony. The population at Baccalieu Island, estimated at 3.3 million breeding pairs in 1984 (Sklepkovych and Montevecchi 1989), had declined to 2.02 million pairs by 2013 (Environment Canada unpublished data), and the former second and third regionally largest colonies have declined by >50% since the late 1990s (Wilhelm et al. 2015, Environment Canada unpublished data). In the eastern Atlantic, the population at St. Kilda is also declining, this being the largest colony in the UK and Ireland (Newson et al. 2008).  Population trends in the Pacific are less well known. In Alaska, where Leach’s Hydrobates leucorhous and Fork-tailed Storm-petrels H. furactus are largely combined for monitoring purposes, population trends are stable or increasing (Slater and Byrd 2009, Dragoo et al. 2016), the large population at Daikoku Island, Japan may have declined since 1982, while trends of western North American and Russian populations are unknown. Despite these knowledge gaps, compiling available data collected between 1977 and 2016, representing 75-80% of the global population (including Europe, eastern North America, and Japan), points to a decline of ≥30% over three generations (39 years, based on a generation length estimated by BirdLife to be 13 years).

Definitive information on Leach’s Storm-petrel population decline comes mainly from colonies within the Atlantic basin.  Recent genetics research indicates that while there is no genetic structure among Atlantic colonies, populations within the Atlantic and the Pacific are genetically distinct (Bicknell et al. 2012).  Evidence of movement of pre-breeding birds among colonies within the Atlantic, led to the conclusion that North Atlantic birds may be operating as a metapopulation and that management of this species may be best viewed at an oceanic scale (Bicknell et al. 2012, 2014).

Trend justification
Data collected from 1977 to 2016 representing 75-80% of the global population, points to a decline of ≥30% over three generations (Huntingdon et al. 1996, Lormee et al. 2012, BirdLife International 2015, Environment Canada unpublished data, Japanese Ministry of Environment, unpublished data). The cause(s) of declines are unknown, but are likely multi-faceted and further research is needed to inform conservation actions.

Distribution and population

This species has an extensive global range. Breeding colonies are largely confined to the northern hemisphere, from the South Kuril Islands (Japan) round to Baja California (Mexico) including the Aleutian Islands, Alaska (U.S.A.) and Canada in the Pacific, and in the north-east North America, Iceland, northern United Kingdom and Norway in the Atlantic. Small numbers also breed off South Africa (Underhill et al. 2002). Northern populations migrate south into the tropics in winter, reaching the equator in the Pacific and as far south as south Brazil and South Africa in the Atlantic (del Hoyo et al. 1992).

Ecology

This species is marine and pelagic, often occurring in areas of convergence or upwelling or over continental shelves, rarely coming near land except at colonies. During the breeding season, birds from the western Atlantic are highly pelagic in their foraging habits, travelling to deep (median >1,950 m) and relatively unproductive waters (chlorophyll a concentrations <0.5 mg/m3) over and beyond continental slopes lying, on average, 400 to 830 km from colonies (Pollet et al. 2014, Hedd et al. 2018). Its diet comprises mainly of small fish, squid, planktonic crustaceans and offal which it catches on the wing by dipping, skimming or snatching from the surface. It sometimes follows marine mammals feeding on leftovers or faeces. Its breeding season is variable depending on locality, forming colonies on offshore islands on high ground or slopes, usually among rocks but also in soft soil between trees (del Hoyo et al. 1992).

Threats

Brown Rats Rattus norvegicus and House Rats R. rattus, are considered to exert a considerable predation pressure on the species where they establish on breeding islands, and may be a key determinant of the present breeding distribution, possibly along with cats. Cats Felis catus predate large numbers of adult and fledgling Leach's Storm-petrels where present, and may have been responsible for the extirpation of the species from a number of formerly occupied sites. Foxes caused the extirpation of the species from numerous islands in Alaska following their introduction, with their eradication on a number of islands leading to subsequent recolonization by Leach’s Storm-petrel. Mice Mus musculus are also suspected to be impacting the species through nest predation, but the effects are unclear.

Leach’s Storm-petrel Hydrobates leucorhous experiences high levels of predation from native predators. In 1997, Herring Gulls Larus argentatus killed almost 49,000 adult petrels during the breeding season on Great Island, Newfoundland, which at the time had a breeding colony of around 270,000 pairs (Stenhouse et al. 2000). Great Skuas Catharacta skua predate Leach’s Storm-petrels, with around 21,000 individuals killed each year in the St. Kilda colony; however, these primarily represent non-breeding birds that had immigrated from other, larger colonies, hence this is thought to have a relatively small impact on the population (Stead 2010). Great Larus marinus and Lesser Black-backed Gulls L. fuscus are also known to predate relatively large numbers of adult Leach's Storm-petrel (Stenhouse et al. 2000), though the extent to which this drives declines is uncertain.

Research activities have been shown to cause considerable disturbance to Leach’s Storm-petrel and represent a cause of reduced reproductive success. In a study by Blackmer (2004), it was found that weekly investigator disturbance halved the hatching success of Leach’s Storm-petrel nests, and daily disturbance caused a 56% reduction. Of all the reproductive failures in this study, egg desertion accounted for 91% and only occurred in pairs in the disturbed treatment groups.

Foraging ranges during the breeding season for five out of seven western Atlantic colonies overlapped with offshore oil and gas operations; three of these colonies have declined in recent decades (Hedd et al. 2018). Attraction to lights and flares and subsequent collisions with oil rigs poses a risk (Hedd et al. 2018). Large oil spills represent a relatively unlikely but potentially very severe threat, although due to this bird’s large range, it would be likely to affect only a small portion of the population. Small spills of hydrocarbons and synthetic drilling fluids are relatively common (CNLOPB 2012, McCrary et al. 2003) and contribute to chronic oil pollution in the sea (National Research Council 1985).

Conservation actions

Conservation Actions Underway
It is listed in Appendix II of the Bern Convention, and Annex I of the EU Birds Directive. The following information refers to the species European range only: it is listed as occurring in nine marine Important Bird Areas in Europe, with sites in Iceland, Ireland and the United Kingdom. In the EU it is listed within 25 Special Protection Areas in France, Ireland, Spain and the United Kingdom. Various countries, including the United Kingdom have introduced artificial nest boxes to breeding colonies to reduce the predation risk and to facilitate monitoring of breeding success (Newson et al. 2008).

Conservation Actions Proposed
Estimates of population size and trend are needed in Europe, western North America, Alaska and Russia. All large breeding colonies in Canada are protected under provincial and/or federal protected area legislation. Additionally, all major Canadian colonies are Important Bird Areas (http://www.ibacanada.ca/). Continued monitoring of adult survival and breeding success are needed at colonies in the western Atlantic and additional information about the threats currently affecting this species is needed across its range.

The following information refers to the species' European range only: continued monitoring of breeding success at colonies, including the provision of artificial nest boxes. Management of invasive predators.

Acknowledgements

Text account compilers
Moreno, R., Stuart, A., Westrip, J., Fjagesund, T., Ekstrom, J., Hermes, C., Calvert, R., Butchart, S., Martin, R., Ashpole, J, Miller, E.

Contributors
Hedd, A., Bond, A.


Recommended citation
BirdLife International (2022) Species factsheet: Hydrobates leucorhous. Downloaded from http://www.birdlife.org on 27/05/2022. Recommended citation for factsheets for more than one species: BirdLife International (2022) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 27/05/2022.