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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4 Responses to Aldabra Fody (Foudia aldabrana): revise global status?

  1. Janske van de Crommenacker says:

    The Seychelles Islands Foundation (SIF) is mandated with the conservation and management of the UNESCO World Heritage Site Aldabra Atoll. SIF is very pleased that the Aldabra fody is brought up as a candidate for up-listing on the IUCN Red List. It’s current status of ‘Least Concern’ applies to the much more widely distributed F. eminentissima, but unlike the latter, the restricted range, relatively small population size, ongoing threat from the presence of introduced feral cats and rats, and from introduction of the Madagascar fody, make the Aldabra fody much more vulnerable to extinction. Therefore we deem the current status of ‘Least Concern’ to be inappropriate, possibly compromising it’s conservation management.

  2. Janske van de Crommenacker says:

    We have now successfully eradicated the Madagascar fody populations on both Aldabra and Assumption, as well as all the hybrids. In case any hybrids would be left, we don’t believe them to be a current threat as they covered only a small area and their numbers are negligible compared to the whole Aldabra fody population. However, re-introduction of Madagascar fodies remains a threat, given their abundance on many other islands in the Seychelles and Western Indian Ocean region, and their ability to hybridize in a relatively short time frame.
    We strongly support that the current status of ‘Least Concern’ should be changed to at least ‘Vulnerable’ to more accurately reflect the Aldabra fody’s biological and geographical situation as well as it’s threat status.

  3. I have reviewed the information here on behalf of the Seychelles Islands Foundation (SIF), which manages Aldabra Atoll, and would like to provide updated information and make the following points as per the criteria listed above:

    Criterion A: It is correct that the species is currently considered to be stable by SIF.

    Criterion B: The extent of occurrence of the Aldabra fody stated here is incorrect. Aldabra has a land area of ~153 km2 so this is the correct extent of occurrence. It is not clear where the larger figure above (390 km2) originates from – could a source be added and checked/updated please? The entire protected area of Aldabra is 433 km2, which includes the marine area. We agree that there remains the possibility of continuing decline in the future; the nesting success of Aldabra fodies is relatively low (only 10% of nests fledged young from 2011 to 2015 [n = 77 nests]; SIF unpubl. data), which is assumed to be primarily due to introduced rat predation, and introduced F. madagascariensis is still common on many other islands in the Seychelles. The introduction of F. madagascariensis and the subsequent rapid eradication of this species from Aldabra was considered a lucky escape as it spread quickly and began hybridising with the Aldabra fody (see van de Crommenacker et al. 2015. Using molecular tools to guide management of invasive alien species: assessing the genetic impact of a recently introduced island bird population. Div Distrib 21: 1414–1427). The successful eradication of F. madagascariensis from Aldabra and Assumption means that this species no longer poses an urgent threat to the Aldabra fody but the presence of the species on other Seychelles islands and the possible introduction of novel pathogens, which were detected in the Assumption population of F. madagascariensis but have never been documented in the Aldabra fodies, remain a possible threat. Under this criteria, the facts therefore support uplisting to either Vulnerable or possibly Endangered.

    Criterion C: SIF finds that the continuing threats to this population and high potential for future population decline warrants listing as either Endangered or Vulnerable. This status should then be revised if and when rats are eradicated from Aldabra (this eradication is currently being considered) and if ongoing monitoring indicates an increase in population size.

    Criterion D: In our view, Aldabra constitutes a single location for the Aldabra fody as the species can easily fly between the four islands (the threats are similarly not usually constrained to separate islands). The channels between the main islands of Aldabra are mostly tens of metres apart (only the Main Channel is larger) and fodies have been observed flying across these channels. There are no captive populations of Aldabra fodies that we are aware of, making Aldabra the only place this species occurs. Under this criterion the species therefore qualifies as Vulnerable.

    To conclude, SIF supports the uplisting of the Aldabra fody to either Vulnerable or Endangered (preferably Endangered) to reflect the nature of the threats still posed to the species, until these threats can be addressed.

  4. Further relevant information concerning increasing threats to F. aldabrana comes from a recent publication (Haverkamp et al. 2017. Giant tortoise habitats under increasing drought conditions on Aldabra Atoll – Ecological indicators to monitor rainfall anomalies and related vegetation activity. Ecological Indicators 80: 354-362). This paper provides evidence of increasing drought conditions on Aldabra with high impacts on the vegetation, especially on the open mixed scrub, an important habitat for the Aldabra fodies. This highlights the increasing threat of climate change impacts on the Aldabra fody population and further supports uplisting of the species status to Vulnerable or Endangered.

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