Aldabra Fody (Foudia aldabrana): revise global status?

Aldabra Fody (Foudia aldabrana) was recently split from F. eminentissima (see forum topic regarding this split here). Endemic to scrub, Casuarina woodland and coconut groves on Aldabra (Craig 2016), this species was assessed when split in 2016 as Near Threatened under criterion D2 (BirdLife International 2017; see also the 2016 forum topic). However, the species may face further threats than just problematic native and introduced predators (which appear to not be leading to population declines). Van de Crommenacker et al. (2015) highlight the impact that an invasive congener (Red Fody, Foudia madagascariensis) could have on this species. Looking at genetic markers, they showed that F. madagascariensis was hybridising with F. aldabrana and thus could be eroding the genetic integrity of this species (van de Crommenacker et al. 2015).

The recognition of this invasion has led to a successful eradication project to remove F. madagascariensis and madagascariensis x aldabrana hybrids from Aldabra (N. Bunbury in litt. 2017); and as such the species may still be considered to not be in continuing decline as a result of this threat (N. Bunbury in litt. 2017). However, the potential impacts of future invasion of F. madagascariensis from Assumption where it was introduced in the 1970s (van de Crommenacker et al. 2015) along with the impacts predators are having on the species (48% of nestlings and 81% of eggs may be taken by predators [Safford 2013]) may mean that the Red List status of this species requires revision. Therefore, we have re-assessed this species against all Red List criteria based on current best information.

 

Criterion A – As the species is currently considered to be stable it would not warrant listing as threatened under this criterion.

 

Criterion B – Aldabra Fody has an Extent of Occurrence of only 390km2, and so meets the threshold for Endangered under criterion B1, and although it has not been calculated yet to IUCN guidelines, its Area of Occupancy likely meets the threshold for Endangered under criterion B2. The species is currently considered stable, yet there remains the possibility of a continuing decline in the future as a result of the potential impacts of F. madagascariensis combined with problematic native and invasive predators. Additionally it is likely found at <5 locations (see Criterion D). Therefore, it could potentially warrant listing as Endangered under criteria B1ab(v)+2ab(v), although this is a pessimistic view based on the potential for future declines and based on the current state of the population Near Threatened under these criteria may be more appropriate.

 

Criterion C – The population size of this species has been estimated at 2,000-6,000 mature individuals (Rocamora and Skerrett 2001). Thus the population size falls at the borderline of the threshold for Vulnerable and Endangered. Criterion C has the same issue as criterion B in that there needs to be a continuing decline. Thus the species could potentially warrant listing as Endangered or Vulnerable under criterion C2a(ii) given the potential for future impacts of F. madagascariensis, although based on the current state of the population Near Threatened under this criterion may be more appropriate.

 

Criterion D – The population size is too large to qualify under this criterion. However, given the potential high threat from F. madagascariensis the number of locations where the species is found may be very small, whether Aldabra atoll itself is considered to be 1 location or if the 4 main constituent islands (Grand Terre Malabar, Picard and Polymnie) are considered separate locations. Therefore, the species may qualify as Vulnerable under criterion D2.

 

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

 

Therefore, it is proposed that this species be at least uplisted to Vulnerable under criterion D2, although we welcome comments regarding the population trend as this may mean that the species may warrant listing as Endangered.

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’s Red List status. Therefore, please make sure your comments are about the proposed listing.

 

References

BirdLife International (2017) Species factsheet: Foudia aldabrana. Downloaded from http://www.birdlife.org on 25/10/2017.

Craig, A. (2016) Red-headed Fody (Foudia eminentissima). 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 http://www.hbw.com/node/60998 on 26 August 2016).

Rocamora, G. & Skerrett, A. (2001) Seychelles. Pp. 751-768 in: Fishpool, L. D. C. and Evans, M. I. (eds), Important Bird Areas of Africa and associated islands, BirdLife International, Cambridge, UK.

Safford, R. J. (2013) Aldabra Fody Foudia aldabrana. Pp. 889-892 in Safford, R. J. and Hawkins, A. F. A. (eds) The Birds of Africa. Vol. VIII: The Malagasy Region. Christopher Helm, London.

Van de Crommenacker, J., Bourgeois, Y. X. C., Warren, B. H., Jackson, H., Fleischer-Dogley, F., Groombridge, J. & Bunbury N. (2015) Using molecular tools to guide management of invasive alien species: assessing the genetic impact of a recently introduced island bird population. Diversity Distrib. 21: 1414-1427.

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