Madagascar Grebe (Tachybaptus pelzelnii): revise global status?

Madagascar Grebe (Tachybaptus pelzelnii) is endemic to Madagascar, generally frequenting shallow freshwater pools and lakes with dense lily pads, although it will occur on brackish and deeper water (del Hoyo et al. 1992, Langrand 1995, Fjeldså 2004, H. G. Young in litt. 2012). The species faces multiple threats particularly from habitat loss as a result of agricultural expansion, the increasing use of pesiticides and herbicides, intensification of fishing, and the introduction of exotic herbivorous fish (Langrand 1995, O. Langrand in litt. 2007, H. G. Young in litt. 2007).

The introduction of fish to certain freshwater areas could also be impacting the species indirectly by benefitting the structurally similar Little Grebe (Tachybaptus ruficollis) as it is more piscivorous than T. pelzelnii. Little Grebe has increased rapidly while Madagascar Grebe has decreased and so it could be that the former is outcompeting the latter, although it could just be wetland alterations benefit Little, while negatively impacting Madagascar Grebe (Safford 2013). Hybridisation between the two grebe species could be an additional threat (Langrand 1995), but at the moment there has been no supporting evidence for this (ZICOMA 1999). Carnivorous fish may also impact the species, e.g. Channa spp. (H. G. Young in litt. 2007), and the species may also suffer mortality from getting caught in gill-nets, and from direct hunting pressure, as it is considered a delicacy (H. G. Young in litt. 2012).

These threats together are thought to be driving declines in the species. It is known to have largely disappeared from areas of formerly occupied habitat (Collar and Stuat 1985), and rates of decline may even increase into the future (see BirdLife International 2018). Additionally, the species is currently assessed as having a small population size, and as such the species is listed as Vulnerable (see BirdLife International 2018). However, it has been noted that the population size could be significantly lower than currently assessed, and past reductions could have been higher than currently thought (M. Rabenandrasana in litt. 2007, A. Bamford in litt. 2018). Therefore, to see whether the species may deserve a higher threat status, we have reassessed the species here against all criteria.

 

Criterion A – The population is known to have declined (Collar and Stuart 1985), and given the ongoing threats it is highly likely that the population continues to decline. Estimating the rate of decline, however, is difficult. Collation of survey information suggests that the population may number only 2,000 individuals (roughly equating to c.1,300 mature individuals), with potentially half of the population potentially restricted to two localities, and the rest of the population scattered across many other sites holding only a handful of individuals (A. Bamford in litt. 2018).

The current population estimate held for this species is 5,000 individuals (roughly c.3,300 mature individuals), and if the two estimates are reliable then the population reduction between the two is 60%. There is some confusion around the year of this first estimate though, due to the interchanging of the use of terms ‘individuals’ and ‘mature individuals’, making it even more difficult to get a quantification of population trend. If, however, we hypothetically use the turn of the millennium as the start point, this would equate to a decline of c.56% over three generations (16.2 years). This would meet the threshold for Endangered, but it had been noted that the population estimate may have been as low as 1,500-2,500 individuals by 2007 (M. Rabenandrasana in litt. 2007), and so rates of decline may in fact be slower.

Further information is therefore required to be able to assess the species more clearly against this criterion. In the absence of this information it may not be possible to list the species under this criterion.

 

Criterion B – While the species’s Area of Occupancy (AOO) has not been calculated per IUCN Guidelines (IUCN Standards and Petitions Subcommittee 2017), its Extent of Occurrence (EOO) is too large to warrant listing under this criterion (689,000km2).

 

Criterion C – The population has been estimated to be only 2,000 individuals (A. Bamford in litt. 2018) (roughly equating to c.1,300 mature individuals), yet in 2007 it was suggested that the population could be as low as 1,500-2,500 individuals (M.  Rabenandrasana in litt. 2007) (roughly equating to 1,000-1,670 mature individuals). Given the uncertainty, and the fact that these are only rough estimates then the current population size may be more appropriately placed in the range 1,000-2,499 mature individuals.

As it is considered to be undergoing a continuing decline, with a population size in the range 1,000-2,499 mature individuals, the species potentially warrants listing as Endangered under criterion C. There is insufficient clear estimates of population trends, so it cannot be assessed against criterion C1, and the species is not considered to undergo extreme fluctuations (fluctuations of an order of magnitude; IUCN Standards and Petitions Subcommittee 2017), so it would not warrant listing under criterion C2b.

The species does breed at several scattered wetlands across Madagascar, but it is dispersive (Llimona et al. 2018) and so separate breeding ‘populations’ could potentially come into contact with one another through dispersing individuals. Therefore, we could precautionarily assess the species as occurring in one interconnected subpopulation, and as such it would warrant listing as Endangered under criterion C2a(ii).

 

Criterion D – With a population size estimate of 1,000-2,499 mature individuals, the species would warrant listing as Near Threatened under criterion D1. The species’s range is sufficiently large that it would not warrant listing under criterion D2.

 

Criterion E – To the best of our knowledge there has been no quantitative analysis of extinction risk conducted for this species. Therefore, it cannot be assessed against this criterion.

 

Overall, therefore, it is proposed that Madagascar Grebe be listed as Endangered under criterion C2a(ii), and potentially under criterion A too. Comments are welcome but please note that this topic is not designed to be a general discussion about the ecology of the species, rather a discussion of the species’ Red List status. Therefore, please make sure your comments are about the proposed listing.

 

References

BirdLife International. 2018. Species factsheet: Tachybaptus pelzelnii. Downloaded from http://www.birdlife.org on 26/03/2018.

Collar, N. J.; Stuart, S. N. 1985. Threatened birds of Africa and related islands: the ICBP/IUCN Red Data Book. International Council for Bird Preservation, and International Union for Conservation of Nature and Natural Resources, Cambridge, U.K.

del Hoyo, J.; Elliot, A.; Sargatal, J. 1992. Handbook of the Birds of the World, vol. 1: Ostrich to Ducks. Lynx Edicions, Barcelona, Spain.

Fjeldså, J. 2004. The grebes. Oxford University Press, Oxford, U.K.

IUCN Standards and Petitions Subcommittee. 2017. Guidelines for Using the IUCN Red List Categories and Criteria. Version 13. Prepared by the Standards and Petitions Subcommittee. Downloadable from http://www.iucnredlist.org/documents/RedListGuidelines.pdf.

Langrand, O. 1995. Recensement des oiseaux d’eau à Madagascar et observation de la Sarcelle de Bernier Anas bernieriMadagascar Region Newsletter 5: 13-14.

Llimona, F.; del Hoyo, J.; Jutglar, F.; Garcia, E. F. J.; Kirwan, G. M. 2018. Madagascar Grebe (Tachybaptus pelzelnii). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from https://www.hbw.com/node/52479 on 26 March 2018).

Safford, R. J. 2013. Madagascar Grebe Tachybaptus pelzelnii Grèbe malgache. Pp 112-114 in Safford, R. J. and Hawkins, A. F. A. (eds) The Birds of Africa. Volume VIII: The Malagasy Region. Christopher Helm, London.

ZICOMA. 1999. Zones d’Importance pour la Conservation des Oiseaux a Madagascar.

This entry was posted in Africa and tagged , . Bookmark the permalink.

One Response to Madagascar Grebe (Tachybaptus pelzelnii): revise global status?

  1. André Konter says:

    I support the proposal that Madagascar Grebe be listed as endangered under criterion C2a(ii), and potentially under criterion A too. Unfortunately, I have no recent data, my last stay in Madagascar dating some 10 years back. Already then, I found the species extremely hard to find and I only encountered a handful of individuals.

Leave a Reply

You have to agree to the comment policy.