Justification of Red List Category
This species has been extirpated from two islands, and breeding is now restricted to an extremely small area on one island, where invasive species are contributing to a population decline. It therefore qualifies as Critically Endangered.
Surveys in 2008 found fewer than 100 breeding pairs on Socorro, suggesting that even accounting for non-breeding birds the total global population may be as low as 250-999 mature individuals, and that previous at sea estimates (which were subject to a high degree of error) may have been too large (J. Martínez-Gomez in litt. 2008). This estimate equates to 375-1,499 individuals in total, rounded here to 350-1,500 individuals.
A rapid population decline over the last three generations is estimated from surveys carried out since 1980, but exact trends are difficult to determine owing to inconsistencies between estimates of the breeding population and total numbers at sea (Brooke 2004). A noticeable reduction in nesting colonies has occurred since the observations of Martínez-Gómez and Jacobsen (2004, J. Martínez-Gómez in litt. 2012).
Puffinus auricularis breeds around Cerro Evermann on Socorro in the Revillagigedo Islands, Mexico. In 1981, the population was estimated at 1,000 pairs, with more found in the north of the island in 1990. In 1993-1999, the estimate was 500 pairs (J. Martínez Gómez in litt. 1998, 1999, 2000). In 2008, fewer than 100 breeding pairs could be located (J. Martínez-Gomez in litt. 2007, 2008, 2009). However, 46,000 individuals (95% CI = 18,000-89,000), including 10,600 breeding birds, were estimated during at-sea censuses in 1980-1994 (Spear et al. 1995). It is clear that the breeding range has contracted, and threats indicate that numbers have declined. The species formerly bred on Clarión and San Benedicto, but was almost certainly extinct on the former by 1988, and there has been no confirmed breeding on the latter since 1952. Birds seen immediately north of San Benedicto in 1988 and 1990 provide some hope that a population remains. In the non-breeding season, it forages largely in waters over the continental shelf of Mexico (Spear et al. 1995).
On Socorro, it breeds in rocky burrows within dense bushy areas at the forest edge. Breeding is concentrated above 700 m (Brooke 2004), but observations in 1981 suggested that the major breeding sites were at 500-650 m. Birds have been seen roosting in the naval base at Cape Rule (J. Martínez Gómez in litt. 1998, 1999, 2000). On Clarión, it nested in burrows on grassy and bracken-covered slopes (S. N. G. Howell in litt. 1998). Birds return to colonies in mid-November with breeding from late January to mid-March (Carboneras et al. 2014).
Invasive species represent the greatest combined threat to this species. Cats were introduced to Socorro in the early 1970s, and more than 92% of cat scats above 500 m contain shearwater remains (J. Martínez Gómez in litt. 1998, 1999, 2000). Most shearwaters are taken by cats when they land in parts of the forest where the understorey is practically absent (Martínez-Gómez and Jacobsen 2004). The introduction of pigs to Isla Clarion in 1979 led to local extinction of the species by 1990 (Howell and Webb 1990, Everett and Pitman 1993). Subsequently pigs have been eradicated from the island and some other shearwater species (though not this species as yet) have been recorded returning to the island to breed (Wanless et al. 2009). Sheep and goats are destroying nesting habitat across some parts of the colonies, through overgrazing and soil compaction (Santaella and Sada 1991). However, the largest breeding grounds were found in the north and northwest of Socorro’s mountain summit where the vegetation has not been severely damaged by introduced herbivores. Feral sheep and goats were completely eradicated from Socorro in 2012, resulting in a rapid and remarkable recovery of the local vegetation cover (Ortiz-Alcaraz et al. 2017). Rabbits were introduced to Isla Clarion in 1979 and caused significant damage to nesting habitat and directly competed with Townsend's Shearwaters for burrows, which is likely to have hastened the extinction of the species on the island (Santaella and Sada 1991, Everett and Pitman 1993). House Mice have also been identified as having a significant negative impact on the species on Socorro (Islands Conservation in prep.). The presence of rats on the island has been reported, but not confirmed, however it is a likely future scenario which would be likely to drive further rapid declines (J. Martínez Gómez in litt. 1998, 1999, 2000).
Other threats include volcanic eruptions – the San Benedicto population was obliterated by a volcanic eruption in 1952 (Everett and Pitman 1993) – as well as sea-level rise and climate change (BirdLife International unpubl. data) and human developments; the construction of a new airstrip in 2009 is believed to have caused the death of an unknown number of birds due to light pollution associated with nocturnal works (Carboneras et al. 2014).
Conservation Actions Underway
In 1994, the Revillagigedo Islands were declared a Biosphere Reserve. There are plans to conduct surveys on Clarión and Socorro, with intensive cat-trapping taking place in 2007, but previous efforts have been poorly resourced (B. Tershy and B. Keitt in litt. 1999, J. Martínez-Gomez in litt. 2007, 2008, 2009). Pigs and sheep were eradicated from Clarión between 2001 and 2004, but attempted rabbit eradication failed. The eradication of sheep from Socorro began in 2009 and should be complete within a few years (A. Aguirre in litt. 2012). Similarly, cat eradication is underway on Socorro (A. Aguirre in litt. 2012). The installation of an automated playback system to assist the recolonisation of Clarión is under consideration (B. Tershy and B. Keitt in litt. 1999).
Conservation Actions Proposed
Eradicate introduced mammals on Socorro and Clarión. Determine whether a breeding population remains on San Benedicto. Assist the recolonisation of Clarión. Continue to monitor numbers on Socorro and at sea. Conduct high-level lobbying to raise awareness of the effect military operations may have on the species.
33 cm. Medium-sized shearwater. Generally black above and white below. Sharp transition at side of head from black (with some freckling) to white. White underparts except for black half-collar, blackish undertail-coverts and thighs. Prominent white flank patch extending to side of rump. Underwing black around leading and trailing borders sharply demarcated from central white areas. Similar spp. Black-vented Shearwater P. opisthomelas is larger, distinctly brownish and has less clear separation of dark and light areas. Voice Braying notes at colony.
Text account compilers
Moreno, R., Stuart, A., Symes, A., Bird, J., Benstead, P., Butchart, S., Clay, R.P., Fjagesund, T., Ashpole, J, Hermes, C., Martin, R.
Tershy, B., Keitt, B., Martínez-Gómez, J.E., Bourne, W., Howell, S.
BirdLife International (2021) Species factsheet: Puffinus auricularis. Downloaded from http://www.birdlife.org on 24/10/2021. Recommended citation for factsheets for more than one species: BirdLife International (2021) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 24/10/2021.