Justification of Red List Category
This species was previously classified as Near Threatened as, although it has a single, small population, it was not thought to be declining. It is now thought to be experiencing a continuing decline owing to deteriorating habitat quality, and probable decreases in survival and breeding success, as caused by human activities and other problematic species, and it has therefore been uplisted to Vulnerable.
In 2003, S. Imberti (in litt. 2003) estimated that perhaps fewer than 5,000 individuals remain. More recently, the total size of the breeding population has been calculated to lie between 3,428 and 3,673 adults (Agüero et al. 2011), and 1,899 juveniles were also counted, giving a total population of c.5,300-5,600 individuals, and 3,400-3,700 mature individuals.
The population is inferred to be experiencing a continuing decline owing to a decline in habitat quality, and probable decreases in survival and breeding success, as caused by human activities and other problematic species. The rate of decline has not been quantified.
Tachyeres leucocephalus was previously considered to be restricted to the south coast of Chubut province, Argentina (Madge and Burn 1988, Carboneras 1992), but it is now known to have a larger range (non breeding and breeding), with occasional sightings along the coastline from the Valdés Peninsula to the Beagle Channel in Tierra del Fuego (Imberti 2003, M. Pearman in litt. 2003). Its breeding distribution is confirmed restricted to approximately 700 km of coastline (Agüero et al. 2011). The population has been estimated to not exceed 5,000 birds (S. Imberti in litt. 2003), and first systematic surveys along the coast of Chubut province from 2006-2008 gave a total estimate of 3,400-3,700 mature individuals (G. Borboroglu in litt. 2008, Agüero et al. 2011), with key populations at Bahía San Gregorio, Bahía Melo and Caleta Malaspina, all located at northern San Jorge Gulf. It appears to occur at very low densities throughout its range, and is inferred to be declining (Agüero et al. 2011).
It is an entirely coastal species, found in rocky areas and sheltered bays, breeding on offshore islands in shallow, protected bays (Agüero et al. 2010).
The restricted range, flightlessness and overlapping distribution with tanker lanes makes the species highly vulnerable to oil spills. Oil exploration activities, which are taking place within 100 km of the species' centre of abundance and sea currents would likely take oil spills from the main area of development towards the species’s range (Agüero et al. 2010, 2011). In the last 30 years, three major oil spills severely affected Steamerduck breeding areas and were reported to cause massive mortalities, and the sediment and rocks within the species’ range are still contaminated with oil derivatives (Agüero et al. 2011). The ongoing threat of chronic oil contamination is considered to have slow or even negligible effects on the population, but future spill events remain a high-level risk.
The species may also be affected by the harvesting of guano and macroalgae (Agüero et al. 2010, 2011), as well as other human activities such small-scale coastal fishing and recreational activities. Egg collecting has been reported, but appears to occur at very low intensity and at a few sites only (Agüero et al. 2010, 2011). A further potential threat stems from three introduced species; the Green Crab Carcinus maenus, Asian Kelp Undaria pinnatifida and the Acorn Barnacle Balanus glandula, all of which may cause dramatic changes to ecosystems upon which Steamerducks depend (Agüero et al. 2010, 2011). The exact impact of these species on the White-headed Steamerduck and the changes they incur on the wider ecosystem is currently unknown. Levels of predation during the breeding season may be increasing with the documented rapid population increase in the population of native Kelp Gulls Larus dominicanus (Agüero et al. 2011). The observation that the species breeds at higher densities on islands could suggest that it is restricted by mammalian predators on the mainland (Agüero et al. 2011), but also indicates its vulnerability to potential introduction of invasive species onto islands. However, the very large number of small islands within the breeding range would reduce the potential scope of this threat.
Conservation Actions Underway
The Interjurisdictional Marine Park in San Jorge Gulf contains about 46% of the entire population (Agüero et al. 2011). The entire breeding range has been included in the UNESCO Biosphere Reserve Patagonia Azul, designated in 2015 (Garcia Borboroglu et al. 2015).
Text account compilers
Martin, R., Moreno, R., Palmer-Newton, A., Sharpe, C.J., Stuart, A., Symes, A., Benstead, P., Capper, D., Anderson, O., Fjagesund, T., Hermes, C., Mahood, S., Mansur, E., Calvert, R.
Pearman, M., Esler, D., Imberti, I., Borboroglu, G.
BirdLife International (2020) Species factsheet: Tachyeres leucocephalus. Downloaded from http://www.birdlife.org on 30/05/2020. Recommended citation for factsheets for more than one species: BirdLife International (2020) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 30/05/2020.