DistributionRead full entry
Range DescriptionThis speciesbreeds on a few basaltic lakes in the interior of Santa Cruz, extreme south-west Argentina; the only known wintering grounds are the ro Coyle, ro Gallegos and ro Chico estuaries on the Atlantic coast of Santa Cruz (Johnson and Serret 1994, Imberti et al. 2004, Roesler et al. 2011b). It is apparently accidental in Magallanes, south Chile (Roesler et al. 2011b), however well-documented observations were made of two individuals using a lake in Laguna Blanca in October 2013 (Saiter in litt. 2013, Schmitt in litt. 2013). The total population was estimated at 3,000-5,000 individuals in 1997 with half of these on Meseta de Strobel (O'Donnell and Fjelds 1997). Counts on the wintering grounds suggested a decline of 40% over a seven year period (S. Imberti in litt. 2006), and surveys conducted in December 2006 and January 2009 that revisited key known breeding sites surveyed in 1987 (Lagunas del Sello, del Islote and Tolderia Grande) and 1998 (Encadenadas) also found sharp declines; numbers fell from 452 to 51 at Laguna del Sello, from 700 to 0 at Laguna del Islote, from 90 to 0 at Tolderia Grande (H. Casaas in litt. 2009) and from 198 to 0 at Lagunas Encadenadas (Konter 2008). During the 2010-2011 breeding season 535 individuals were counted, indicating a population decline of more than 80% over the last 26 years (Roesler et al. 2011b).
In 2013, greater resources allowed a simultaneous count across all plateaus known to have ever held grebes and visiting virtually every lake with historic records of the species, resulting in a count of 691 adults and 144 chicks in 12 colonies (Casaaset al.2013). During the summer of 2014/2015, 771 adults, 138 juveniles and 12 colonies were recorded across 18 lakes (Roesleret al. 2015). Three new lakes holding the species were identified, however on the Strobel plateau the number of lakes holding the species decreased.In both the 2009/2010 and 2010/2011 breeding seasons, the species was most abundant on three plateaus: Buenos Aires, Strobel and Siberia,with five lakes holding almost 85% of the population (Roesler et al. 2012). A population decline between 1984/1985 and 2010/2011 was not detected on the Buenos Aires plateau but there was a very strong decline (96%) on Strobel plateau (Roesler et al. 2012). While there is speculation that numbers fluctuate dramatically at breeding sites from year to year driven by movements rather than actual population fluctuations (Fjelds 1986), overall declines detected on the wintering and breeding grounds appear to be real and rapid (Roesler et al. 2011b). Examination of photographs from the 1980s suggests that P. gallardoi was formerly the commonest waterbird on its core breeding grounds, the Buenos Aires, Strobel and San Martin plateaus; the 2009 surveys visited two of these areas and recorded the declines above as well as noting that a number of former breeding sites were completely dry.