The hooded grebe (Podiceps gallardoi ), is a medium-sized grebe found in the southern region of Argentina. It grows to about 32 cm (13 in) in length, and is black and white in color. It is found in isolated lakes in the most remote parts of Patagonia and spends winters along the coast of the same region. In 2012 IUCN uplisted the species from Endangered to Critically Endangered.
The main features of the hooded grebe's appearance which can be used for identification.
The hooded grebe can be found in basaltic lakes during the breeding season. At the moment, the only recorded wintering sites are estuaries on the Atlantic coast of Argentina.
The breeding sites of this species are basaltic lakes in Santa Cruz, south-west Argentina and the wintering grounds are the río Coyle, río Gallegos and río Chico estuaries on the Atlantic coast of Santa Cruz. The species is also thought to be accidental in Magallanes, south Chile. Observations of two individuals have also been made from a lake in Laguna Blanca in October 2013.
During the breeding season the hooded grebe is found on basaltic lakes in the Patagonian steppes at elevations of 500–1,200 m. Both saline and bitter salt lakes are used by non breeding flocks and some birds which winter on the coast of Argentina. The grebe requires aquatic vegetation in its breeding lakes (primarily Myriophyllum elatinoides ) which it uses to build its nest. The vegetation is also the habitat of the aquatic invertebrates on which the hooded grebe feeds. For example, in the week after hatching the chicks are fed aquatic beetles (Limnaea spp.). Nesting takes place in colonies of up to 130 pairs from October to March. However, its rate of reproduction is very low as the average number of young reared per adult is 0.2 annually. Despite the lack of breeding success, the resources required for adult survival are abundant and this has resulted in a low adult mortality rate.
At all stages of the grebe's life it is vulnerable to predation by the American Mink. When the Mink first arrived in 2010-2011 on the Buenos Aires plateau, it killed more than half the adults in a breeding colony of two dozen nests. In 2012 to 2013 more losses to one Mink occurred with 15 adults and 7 juveniles killed at El Cervecero and 10 adults and 5 chicks killed at the C199 colony in La Siberia plateau. As most of the grebe population is currently in the Buenos Aires plateau the grebe is under serious threat by the Mink. The American Mink also carries out surplus killing, thus meaning that a single Mink may result in the loss of whole grebe colonies.
Other threats to the grebe population are; excessive grazing by sheep (this leads to erosion at land shores and limits the growth of vegetation), attacks by Flying steamer ducks (Tachyeres patachonicus ) and predation by Kelp Gulls. Volcanic eruptions in the area may have a negative short-term effect on population size due to heavy ash fall. However, ash also results in a long-term increase in the productivity of the wetlands.
In 1997 the total population size was estimated to be 3,000-5,000 individuals and half of these were on Meseta de Strobel. However, recent counts on wintering grounds have suggested a 40% decline occurring on the wintering grounds over a period of seven years. Additionally, surveys that were conducted in December 2006 and January 2009 revisited key known breeding sites initially surveyed in 1987 and 1998 also uncovered sharp population declines with numbers falling from 452 to 51 at Laguna del Sello, 700 to 0 at Laguna del Islote, 90 to 0 at Tolderia Grande and from 198 to 0 at Lagunas Encadenadas. Similarly, individuals were counted during the 2010-2011 breeding season and it was found that there has been a population decline of over 80% occurring over the last 26 years.
In 2013 a simultaneous count across all plateaus known to have ever held grebes and virtually every lake which has historic records of the species was made. The results of this study indicated a count of 691 adults and 144 chicks in 12 colonies. Furthermore, in the summer of 2014/2015 771 adults, 138 juveniles and 12 colonies were counted across 18 lakes and 3 new lakes holding the species were identified. On the other hand, on the Strobel plateau the number of lakes holding the species decreased.
In the 2009/2010 and 2010/2011 breeding seasons the species was the most abundant on the plateaus Buenos Aires, Strobel and Siberia - where five lakes contained almost 85% of the population. There was no population decline recorded on the Buenos Aires plateau between 1984/1985 and 2010/2011, however a very strong decline was detected on the Strobel plateau (96%). However, it is speculated that the annual fluctuating numbers at breeding sites are driven by movements rather than an increase or decrease in population size. Despite this, the overall decline in population which was detected on wintering and breeding grounds appears to be real and is rapidly occurring.
The hooded grebe is threatened by climate change and the introduction of trout and salmon to the Strobel plateau. Surveys made in 2006, 2009 and 2010–2011, found some lakes completely dry and with water levels 2–3 metres (6 ft 7 in – 9 ft 10 in) lower than in previous years. In addition, winter snowfall has reduced without a corresponding increase in precipitation at other times of the year.
Predation by kelp gulls (Larus dominicanus ) at some lakes, predation by the recently introduced American mink, the excessive grazing by sheep and low breeding potential have been cited as threats.
