Archived 2011-2012 topics: Hooded Grebe (Podiceps gallardoi): does it qualify as Critically Endangered?

Initial deadline for comments: 31 January 2012 [note that this has been moved back by about two months].

BirdLife species factsheet for Hooded Grebe

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.

References:

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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3 Responses to Archived 2011-2012 topics: Hooded Grebe (Podiceps gallardoi): does it qualify as Critically Endangered?

  1. All news received from Patagonia in recent years confirm Joe Taylor’s analysis and I completely agree to the conclusion that the Hooded Grebe qualifies for being listed as Critically Endangered.

    André Konter

  2. Joe Taylor says:

    The following text has been extracted from the manuscript of a forthcoming paper written by Ignacio Roesler, Santiago Imberti, Hernán Casañas and Juan Carlos Reboreda, sent on 5 December 2011:

    Winter counts. During the winter seasons of 2010 and 2011 we conducted intensive counts along the Atlantic Ocean coast of Santa Cruz, Tierra del Fuego and extreme southern Chile. On July 8th 2010 we found c. 737 individuals at Coyle river estuary and on July 29th we detected c. 667 at Río Gallegos river estuary. In 2011 we conducted two simultaneous censuses at both estuaries, the first on May 19th when we found 449 and 310 adult individuals at Coyle and Rio Gallegos river estuaries, respectively and the second on July 16th when we found 77 and 5 individuals in these estuaries. On July 16th 2011 we found a third wintering locality, at the mouth of the Río Chico River into the Santa Cruz river estuary, with 14 individuals. During the winter counts of 2010 and 2011 we did not observe juvenile Hooded Grebes.

    The high variation in the number of individuals found in censuses conducted in a single spot at relatively close dates suggest that winter counts are not appropriate to estimate population trends. The pattern of daily movements of Hooded Grebes in and out of the estuaries are yet unknown and therefore, until data from satellite trackers becomes available, we considered that the numbers obtained during these censuses could only be used as a rough estimator of the minimum population size, which at present would be 759 adults.

    During the breeding season of 2010-2011 we monitored 181 lagoons and found 535 individuals in 14 lagoons. In this season we visited 66 of the 90 lagoons that had been visited in 1984-1985. We found a total of 471 Hooded Grebes in 10 of the 66 lagoons (31 lagoons were dry and 25 did not have Hooded Grebes). In contrast, during the 1984-1985 summer count 2471 adult Hooded Grebes were observed in 56 of these 66 lagoons (Figure 3) which indicate a decline of more than 80% in population size during the last 26 years.

    IUCN Criteria Applications
    Criteria A.2. Population drop: An estimate[d] 81% population reduction within 26 years. Considering the extremely low (or even [nil]) breeding success of the species in the recent breeding seasons (2008-2009, 2009-2010 and 2010-2011) the average age of the population is probably increasing, with the younger individuals probably 4 years of age or more. The average life [span] of similar sized grebes is 5-6 years in P. grisegena (c. 1000 grs.) (Stout & Nuechterlein 1999), 5 years in P. auritus (300-500 grs.) (Stedman 2000), and although yet unknown there is a breeding 12 years old female of P. nigricollis (250-600 grs.) (Cullen et al. 1999). Fjeldså (1986) suggested that Hooded Grebe’s life strategy is based on the survival of adults in detriment of nests and chicks. Consequently, it is probable that life [span] of any species with such strategy would be greater than similar-sized close related species. We consider that a life span of over 10 years is highly likely, even more considering the natural lack of adults’ predators. Nowadays, life span would probably decrease due to expansion of predators such as American Mink and Rainbow Trout. The median age of the population is probably between 6 and 8 years, mainly because the lack of recruitment in the three previous years. Considering the data presented in this report we consider that three generations would be 18-24 years, and thus the reduction detected by us is a bit more than 80% in almost 3 generations.

    It is imperative to mention that the population seems to be getting older, and unless there will be some recruitment in the near future it is possible that the population reduction by senescence will increase. We consider that the average of 40% population reduction per decade was not linear, and probably it has increased within the last decade due to Increase in the population of Kelp Gulls, introduction of Rainbow Trouts, invasion of American Mink and the heavy drought that it is currently affecting the breeding areas.

    As mentioned above, none of the threats seems to be diminishing and in most cases they seem to increase (e.g. wind, drought, etc.). Furthermore, new threats have been detected during our censuses (e.g. American Mink, probable competence with waterfowl). The volcanic activity is not a threatening factor for a well shaped population, but the probability of Hudson’s eruption could become a serious threat for the only good and reproductive population that inhabits the Buenos Aires plateau. The catastrophic natural events could become serious threats for species with extremely low population numbers, like the Hooded Grebe.

    Criteria E. Considering that the estimated reduction, based on direct counting of mostly the complete population, had been of nearly an 80% within the last three generation, we think that the possibilities of extinction within the next three generation is highly above a 50%, due to the threats seems to remain stable or even increasing, and that new threats are appearing.

    • Joe Taylor says:

      Please note that the application of criterion E is normally carried out in reaction to the results of a quantitative analysis, most likely population viability analysis (PVA).

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