Initial deadline for comments: 31 January 2012 [note that this has been moved back by about two months].
Hooded Grebe Podiceps gallardoi is restricted during the breeding season to a few basaltic lakes in the interior of Santa Cruz, extreme south-western Argentina, with a few records in southern Chile, and is known to winter at only two sites, namely the río Coyle and río Gallegos estuaries on the Atlantic coast of Santa Cruz (Johnson and Serret 1994, Imberti et al. 2004).
This species was uplisted in the 2009 Red List update from Near Threatened to Endangered under criteria A2b,c,e; A3b,c,e; A4b,c,e, on the basis that survey results from the species’s wintering grounds appeared to indicate a decline of c.40% since the late 1990s, equating to a decline of 72.5% over 21 years (estimate of three generations), assuming an exponential trend. Recent surveys of its breeding grounds appeared to support the suspicion of a very rapid decline, although it is thought likely that this species moves between breeding sites on an annual basis. The recorded declines appear to be due to the effects of land erosion, potential competition with other waterfowl, predation by Kelp Gulls Larus dominicanus, climate change and its impacts on precipitation and water levels, and the introduction of salmon and trout (S. Imberti in litt. 1999, Imberti and Casañas 2010, Roesler et al. 2011). Recent fieldwork has uncovered another threat, that of predation by the introduced American mink Mustela vison (Roesler et al. 2011). In a newly visited area of the Buenos Aires plateau, a single mink was seen to kill more than half of the adult Hooded Grebes in a breeding colony containing 24 nests. Breeding attempts are also hindered by wind damage (Roesler et al. 2011).
The results of surveys conducted on more than 50 lakes and lagoons that could hold breeding populations, including the six key waterbodies that held c.40% of the total population in the 1980s, suggest that the rate of decline may have been more rapid than previously thought (Imberti and Casañas 2010). When mean counts from the 1980s are summed across these six main sites, an average total of 1,832 adults are estimated to have been recorded; however, surveys at these same sites in 2009 yielded records of only 117 adults. Furthermore, an estimated total of c.580 nests were recorded on average at these six sites during the 1980s, with not one found during the surveys in 2009 (Imberti and Casañas 2010). The difference in the number of adults recorded suggests that a decline of c.94% has occurred at these sites over c.24 years. This equates to a decline of 90.5% over the past 21 years, assuming an exponential trend.
The number of adults recorded during the 2009 surveys, at only 117 (Imberti and Casañas 2010), also raises concerns over the current population size. BirdLife International currently estimates the number of mature individuals at 250-2,499, based on an estimate of 3,000-5,000 individuals in 1997 (O’Donnell and Fjeldsa 1997), and factoring in recorded declines and some difficulty in accessing all potential breeding locations. Recent fieldwork has resulted in an estimate of c.1,000-1,200 individuals (Roesler et al. 2011). However, given the results of the 2009 surveys, there seems to be a real danger that there are fewer than 250 mature individuals remaining.
The judging of population trends in this species is hindered by a poor understanding of inter-annual variation in the distribution of breeding pairs, as well as the remoteness of its breeding habitat, raising concerns over the true coverage of survey efforts. However, it is suggested that the species could qualify as Critically Endangered under criteria A2b,c,e; A3b,c,e; A4b,c,e, on the basis that the species might be suspected to have declined by more than 79% over the past 21 years. Comments on this potential category change are invited and further information is requested on this species, including estimates of the number of mature individuals.
Imberti, S. and Casañas, H. (2010) Hooded Grebe Podiceps gallardoi: extinct by its 50th birthday? Neotropical Birding 6: 66-71.
Imberti, S., Sturzenbaum, S. M. and McNamara, M. (2004) Actualización de la distribución invernal del macá tobiano (Podiceps gallardoi) y notas sobre su problemática de conservación. Hornero 19: 83-89.
Johnson, A. and Serret, A. (1994) Hooded Grebe wintering grounds discovered. Cotinga 2: 9.
O’Donnell, C. and Fjeldsa, J. (1997) Grebes: a global action plan for their conservation.
Roesler, I., Casañas, H. and Imberti, S. (2011) Final countdown for the Hooded Grebe? Neotropical Birding 9: 3-7.
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