Rationale
(Changed due to Change in threat status criteria and increased knowledge)
The regional population of Leach's Storm Petrel Oceanodroma leucorhoa satisfies several criteria for regionally Critically Endangered status. The population size is estimated to number <50 mature individuals. It has undergone a continuous decline of at least 25% within one generation, and a continuing, observed decline has been observed in numbers of mature individuals. In addition, no sub-population is estimated to contain more than 50 mature individuals, and at least 90% of mature individuals occur in a single sub-population.
Distribution
The nominate subspecies breeds during the boreal summer at islands in the North Atlantic and North Pacific oceans dispersing over tropical and subtropical waters of the Atlantic and Pacific oceans (Ryan and Whittington 1997). It is a common summer visitor to the deeper waters off the west and south coasts of southern Africa but scarce off the continental shelf (Ryan and Whittington 1997). Breeding in South Africa has been confirmed at two locations: Dassen and Dyer islands (Whittington et al. 1999). The two sites represent the only known breeding locations in the Southern Hemisphere (Kemper et al. 2007) although the use of offshore islands and predominantly nocturnal activity of breeding birds could raise the question of other southern hemisphere breeding sites yet to be discovered (Ryan and Whittington 1997). All four of the islands are part of the IBA network. Jutten and St Croix islands fall within National Parks, one of which is also a Ramsar site, while both Dassen Island and Dyer Island are Provincial Nature Reserves.
Population
The global population has been estimated at 10 million pairs (Brooke 2004). The sedentary breeding population on South Africa's offshore islands is treated separately from the non-breeding migratory population. Birds were first confirmed breeding in South Africa in 1996 at Dyer Island (Whittington et al. 1999) although 17 birds were detected on this island in 1995. There were c. 20 pairs at Dyer Island in 1998, with breeding also taking place at Dassen Island (Crawford et al. 2012). Breeding ceased at Dyer Island in 2005 (Crawford et al. 2012) with only a small population of five pairs remaining at Dassen Island. The regional population is estimated at c. 10 mature individuals. The confidence in this regional population estimate is high.
Population trend
The global population is considered stable (BirdLife International 2014), while the regional population is experiencing a decline. The number of pairs breeding decreased from an average of 18 during 1995/96-1999/2000 to an average of six from 2002/03-2006/07 (Kemper et al. 2007). In 2005 and 2006, breeding was reported to have ceased at Dyer Island and was only reported at Dassen Island (Kemper et al. 2007). The confidence in regional population trend estimate is high.
Threats
The primary threat to Leach's Storm Petrel occurs during the initial phases of prospecting for potential nest burrows and mates, principally from capture by avian predators, such as Kelp Gulls; in addition, it is potentially also predated upon by domestic cats Felis catus (Underhill et al. 2002). Additional threats include potential disturbance at breeding sites due to island based tourism, a lack of suitable protected breeding sites and occupation of favoured breeding sites (dry stonewalls) by cormorants.
Conservation
Underway
No species-specific conservation measures are underway. Dassen Island is listed as a Provincial Nature Reserve established under Section 6 the Nature Conservation Ordinance, 1974, on 9 March 1998 and proclaimed in the Provincial Gazette of 18 March 1988 by Proclamation No. 23/1988.
Proposed
A Population and Habitat Viability Assessment (PHVA) is recommended, as is a Biodiversity Management Plan. The provision of artificial nestboxes to increase the number of suitable nesting sites should be considered, as this may be a limitation to the size of the population.
Research
* The regional population size needs to be determined and monitored on a regular basis.
* An investigation into the suspected population decline needs to be undertaken; in particular, the correlation between Leach's Storm Petrel and Kelp Gull should be researched.
* A thorough taxonomic assessment of the status of the regional population is required.
* The non-breeding distribution of the regional population needs to be determined.
