The Ringed Storm-petrel (Hydrobates hornbyi) has been observed in thousands in the eastern Pacific Ocean, from 0°S to 35°S along the coast of Ecuador, Peru and Chile (Spear and Ainley 2007, Onley and Scofield 2007). Brooke (2004) suspected the global population to number at least thousands of individuals, and probably tens of thousands, and marine surveys in the 1980s-1990s led to an estimated abundance of 637,200 in spring (95% CI: 0.5-0.8 million) and 1,011,900 in autumn (95% CI: 900,000-1,500,000) (Spear and Ainley 2007).
The species’s breeding sites are poorly-known. The species has been considered likely to breed in the coastal desert of southern Peru and northern Chile (Brooke 2004, Carboneras et al. 2019), and the species’s at-sea distribution and observations of grounded birds have indicated that it nests between 20° and 25°S in Chile and in Peru (Murillo et al. 2013). Since no large colonies have been found, it has been speculated that the species breeds in ‘small, scattered groups’ (Brooke 2004). Individuals have been reported inland at Caraz, Peru, c. 100 km from the coast and at an altitude of 2,250 m (Gardner 1986 in Brooke 2004) and in the Peruvian Andes from Huaraz to Arequipa, at altitudes of 2,300-3,400 m (Murillo et al. 2013). Adults and fledglings attracted to lights have been recorded in localities in desert areas across a broad area of southern Peru (Huarmey, Lima, Lunahuana, Arequipa, Moquegua, Ite and Tacna [Koepcke 1964, Drucker and Jaramillo 2013, Murillo et al. 2013, eBird 2017, Barros et al. 2018]) and northern Chile (Arica, Iquique, Tocopilla, Michilla, Mejillones, Antofagasta, Baquedano, Sierra Gorda and La Negra [Brooke 2000, Brooke 2004, Gómez 2012, eBird 2017, Barros et al. 2018]).
However, no breeding birds had been recorded until a series of surveys was carried out along 780 linear kilometres of the Atacama Desert in northern Chile between 2013-2017. The surveys discovered 25 cavities with signs of storm-petrel breeding activity in the area of Pampa de Indio Muerto, 20 km north of the city of Diego de Almagro, and later captured one H. hornbyi individual at a site 75 km from the coast and at 1100 m above sea level (Barros et al. 2018). The breeding cavities were located in outcrops of gypsum in an area of pampa, and the authors noted that the breeding area could be much larger than that discovered, based on the large area of similar habitat that was not surveyed (Barros et al. 2018).
The species is thought to be threatened by light pollution, which disorientates juveniles, potentially leading to death (Murillo et al. 2013). Dozens of juveniles of this species were recovered in Lima city between 2009 and 2012 (Murillo et al. 2013). Light pollution has been shown to pose a threat to closely-related species when a high enough proportion of the total population has been affected (Rodriguez et al. 2017). Mining and the development of solar energy, roads and power lines may threaten the species’s breeding sites in the Atacama desert (Barros et al. 2018, 2019).
H. hornbyi is currently listed as Data Deficient. Now that more information has been obtained on the species, we are undertaking a full review of the species’s Red List status. Our current information on the species’s conservation status will now be compared to all Red List Criteria.
Criterion A – We have no data on population trends. The species may be declining as a result of threats, including light pollution, but since we have no data from which to quantify population trends, the species cannot be correctly assessed against Criterion A.
Criterion B – The species has a large at-sea range and its Extent of Occurrence (EOO) is estimated at c. 2,761,700 km2. This does not approach the threshold for listing the species as threatened under Criterion B1. The species is therefore assessed as Least Concern under this criterion.
The species’s Area of Occupancy (AOO) has not been quantified. To date, only one breeding colony has been located, and the area of this colony may have a very small area that would fall beneath the thresholds for threatened categories under Criterion B2. However, this species’s population has been estimated to number in the thousands and probably tens of thousands (Brooke 2004), with abundance at sea in spring estimated at 0.5-0.8 million individuals (Spear and Ainley 2007). Based on this range of population estimates, the species can be inferred to breed over a larger area than that of the breeding colonies discovered so far. Furthermore, since a large colony would likely have been detected, it has been supposed that the species may breed in ‘small, scattered groups’ (Brooke 2004).
Surveys of the closely-related Markham’s Petrel H. markhami, which breeds in a similar habitat in the Atacama Desert, found colonies with densities of between 2.2 and 248.15 pairs per hectare, with a mean density of 182 pairs per hectare (Barros et al. 2019). Based on the abundance estimates of Spear and Ainley (2007) and assuming the abundance in spring to represent mature individuals and that all mature individuals are breeding, the area of breeding colonies can be tentatively calculated at between 10 km2 and 1,800 km2.
Whilst it is not in fact likely that all mature individuals are breeding, AOO figures should be calculated at a scale of 4 km4 grid cells, so rescaling the area of breeding colonies to the required scale would likely inflate the figures given above. If we assume that the species has ‘small, scattered colonies’, each of which must contribute at least 4 km2 to the species’s AOO, then we can conclude that the AOO is unlikely to fall beneath 10 km2. From these extremely preliminary figures, the species’s AOO is assessed as falling within a range that may qualify the species as Vulnerable, Near Threatened or Least Concern under Criterion B2. Yet, to list the species as threatened on the Red List under Criterion B, two of conditions a-c must also be met.
Storm-petrels are highly mobile and the species’s population is not likely to be severely fragmented. The number of locations is difficult to quantify because it is determined by the ‘geographically or ecologically distinct area in which a single threatening event can rapidly affect all individuals of the taxon present’. If we assume that the species has ‘small, scattered colonies’ and that none of these are likely to be impacted by the same threats, then the species would likely have more than ten locations. However, if the colonies are concentrated in one or several geographic areas, in which a threat such as light pollution from a city could potentially affect a high proportion of breeding individuals, then the number of locations could be lower.
We have no quantified data from which to estimate, infer or project a continuing decline. Individuals are known to be affected by light pollution (Murillo et al. 2013), which has impacted on other closely-related species (Rodriguez et al. 2017), so we could suspect that this threat is causing a decline in mature individuals in this species. Additionally, the breeding colonies may be affected by mining and development (M. Ramirez in litt. 2019). If there is further evidence to indicate an ongoing decline in the area or extent of the species’s breeding habitat, than condition b may be met. If not, then declines are only suspected and condition b is not met. There is no evidence that the species’s population or range size are undergoing extreme fluctuations. Condition c is not met.
Based on current evidence, the species may qualify as Near Threatened as it potentially meets the area threshold for listing as Vulnerable under Criterion B2, but it is unclear whether condition a is met and a continuing decline is currently only suspected. Should further information indicate that the species has fewer than ten locations, and allow us to observe, estimate, infer or project a continuing decline, the species could qualify for listing as Vulnerable under Criterion B2ab. Conversely, if we conclude that the species is likely to have significantly more than ten locations, then the species may be assessed as Least Concern under Criterion B.
Criterion C – Marine surveys in the 1980s-1990s led to an estimated abundance of 637,200 in Spring (95% CI: 0.5-0.8 million) and 1,011,900 in autumn (95% CI: 900,000-1,500,000) (Spear and Ainley 2007). Assuming the lower population estimates in spring represent mature individuals, we can derive from these surveys a population estimate of 500,000-800,000 mature individuals. These figures do not meet or approach the threshold for listing the species as threatened under Criterion C. The species is assessed as Least Concern under this Criterion.
Criterion D – The population estimate of 500,000-800,000 mature individuals does not meet or approach the population threshold for listing the species as threatened under Criterion D. Although the species may have a highly restricted AOO or number of locations, the species’s is likely to breed in ‘small, scattered groups’ (Brooke 2004), so it is unlikely that there is a plausible future threat that could drive the species to Critically Endangered or Extinct within one generation (16 years). Therefore, the species is assessed as Least Concern under Criterion D.
Criterion E – To the best of our knowledge no quantitative assessment of the probability of extinction has been conducted for this species, and so it cannot be assessed against this criterion.
To allow us to achieve a clearer assessment of the species’s status, information is requested on:
- the size of the area occupied by the species’s breeding colonies.
- trends in the species’s population and in the area and quality of its habitat.
- threats affecting the species and its habitat, and the areas and rates of impact of these threats.
Please note that this topic is not designed to be a general discussion about the ecology of the species, rather a discussion of the species’s Red List status. Therefore, please make sure your comments are about the proposed listing.
An information booklet on the Red List Categories and Criteria can be downloaded here and the Red List Criteria Summary Sheet can be downloaded here. Detailed guidance on IUCN Red List terms and definitions and the application of the Red List Categories and Criteria can be downloaded here.
Barros R., F Medrano, R. Silva & F. de Groote. (2018) First Breeding site record of Hornby’s Storm Petrel Oceanodroma hornbyi in the Atacama Desert, Chile. Ardea 106(2): 203-207.
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Brooke, M. de L. (2004) Albatrosses and Petrels Across the World. Oxford University Press, Oxford.
Carboneras, C., Jutglar, F., Kirwan, G.M. & Sharpe, C.J. (2019) Ringed Storm-petrel (Hydrobates hornbyi). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from https://www.hbw.com/node/52601 on 9 May 2019).
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