West Indian Whistling-duck (Dendrocygna arborea): revise global status?

BirdLife species factsheet for West Indian Whistling-duck

West Indian Whistling-duck (Dendrocygna arborea) occurs in the Caribbean. It is found in the Bahamas, on Turks and Caicos, as well as on the Greater Antilles and Lesser Antilles south to Guadeloupe. The global population is estimated at 10,000-19,999 individuals (L. G. Sorenson in litt. 2007, L. Mugica in litt. 2011), which roughly equates to 6,000-15,000 mature individuals. The largest population of up to 14,000 individuals is found in Cuba (Acosta-Cruz and Mugica-Valdés in litt. 2006). A further 1,500 individuals occur in the Bahamas; 4,500 individuals are found on other islands. Overall, the estimate of the global population size is conservative; it may be revised upwards if more recent estimates become available.

West Indian Whistling-duck inhabits mangroves, reeds and swamps; at dusk it forages in freshwater, brackish and saline ponds or tidal flats (Sorenson et al. 2004, L. G. Sorenson in litt. 2007). The species tolerates or even favours man-made habitats like dams or agricultural fields (Carboneras and Kirwan 2019).

Once abundant and widespread, West Indian Whistling-duck has declined throughout most of its range in the past. The species is threatened by the loss and degradation of wetland habitat, predation by introduced mammals, hunting, as well as increasing droughts and sea-level rise associated with climate change (Staus 2005, Neelin et al. 2006, L. G. Sorenson in litt. 2007, 2012). Despite these threats, the population is increasing at a moderate rate, owing to conservation efforts throughout the range (L. G. Sorenson in litt. 2012). Since 1997, environmental education and awareness campaigns are carried out, which proved successful in changing attitudes and so far encouraged the creation of protected areas and reduced illegal hunting of the species (Sorenson et al. 2004, Lawrence 2019).

West Indian Whistling-duck is currently listed as Vulnerable under Criterion B2ab(i,ii,iii,iv) (BirdLife International 2019). However, reviewing our information about the population trend and distribution range of this species, it seems like both category and criterion have been applied too precautionarily, particularly as we do not have reliable data on the Area of Occupancy of the species. West Indian Whistling-duck appears to warrant a change in Red List status. Therefore, we present here our reassessment against all criteria for the species.

Criterion A – The declines seem to be historical, and the population is currently assumed to recover due to intense conservation action. The population is estimated to increase at a rate of 10-19% over three generations (15.9 years). Overall, the species would not warrant listing as threatened under Criterion A. However, the species may have qualified as threatened under this criterion were it not for continued conservation efforts. Therefore, West Indian Whistling-duck may be precautionarily listed as Near Threatened under Criterion A2cde.

Criterion B – The Extent of Occurrence (EOO) has been calculated as 1,260,000 km2, which is far too large to meet the threshold for Vulnerable under Criterion B1 (EOO < 20,000 km2). As such, West Indian Whistling-duck may be listed as Least Concern under Criterion B1. The Area of Occupancy (AOO) has not been estimated. Records suggest that the species is widespread throughout the Caribbean, from Bahamas and Turks and Caicos through the Greater Antilles to the Lesser Antilles (eBird 2019). Therefore, the previous assumption of an AOO of less than 2,000 km2 is no longer tenable; in fact, we do not have a value for the AOO of the species. Thus, it cannot be assessed against Criterion B2.

Criterion C – The population size is estimated at 6,000-15,000 mature individuals. Even though the lower end of the estimate meets the threshold for listing under Criterion C (< 10,000 mature individuals), the population is increasing and therefore does not meet sufficient conditions to warrant listing as threatened. Hence, the species may be considered Least Concern under this criterion.

Criterion D – The population size and range of West Indian Whistling-duck is too large to warrant listing under Criterion D (< 1,000 mature individuals). As such, the species may be considered Least Concern under this criterion.

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 West Indian Whistling-duck (Dendrocygna arborea) be listed as Near Threatened under Criterion A2cde. We welcome any comments on this proposed listing.

Please note that this topic is not designed to be a general discussion about the ecology of the species, rather a discussion of its Red List status. Therefore, please make sure your comments are relevant to the discussion outlined in the topic.

An information booklet on the Red List Categories and Criteria can be downloaded here and the Red List Criteria Summary Sheet can be downloaded here. Detailed guidance on IUCN Red List terms and definitions and the application of the Red List Categories and Criteria can be downloaded here.

References

BirdLife International. 2019. Species factsheet: Dendrocygna arborea. http://www.birdlife.org. (Accessed 15 April 2019).

Carboneras, C.; Kirwan, G. M. 2019. West Indian Whistling-duck (Dendrocygna arborea). 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, Spain. https://www.hbw.com/node/52800 (Accessed 15 April 2019).

eBird. 2019. eBird: An online database of bird distribution and abundance [web application]. eBird, Ithaca, NY, U.S.A. http://www.ebird.org (Accessed 15 April 2019).

Lawrence, N. 2019. Conserving West Indian Whistling-ducks on Antigua and Barbuda’s Offshore Islands. Final Report. Conservation Leadership Programme.

Neelin, J. D.; Münnich, M.; Su, H.; Meyerson, J. E.; Holloway, C. E. 2006. Tropical drying trends in global warming models and observations. Proceedings of the National Academy of Sciences 103(16): 6110-6115.

Sorenson, L. G.; Bradley, P.E.; Sutton, A.H. 2004. The West Indian Whistling-duck and Wetlands Conservation Project: a model for species and wetlands conservation and education. Journal of Caribbean Ornithology 17(Special issue): 72-80.

Staus, N. L. 2005. West Indian Whistling-duck Dendrocygna arborea. In: Kear, J. (ed.). Ducks, Geese and Swans, pp. 197-199. Oxford University Press, Oxford, U.K.


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11 Responses to West Indian Whistling-duck (Dendrocygna arborea): revise global status?

  1. Numbers in Puerto Rico are higher than thought. We estimated around 200 in the southwestern portion (Laguna Cartagena and Boquerón) and at least 100 in the northwest area (Cano Tiburones). Total population is likely between 300-400 individuals. We have documented 7 nests since 2013 producing 36 ducklings.
    Note:

    James T. Anderson, Nickolas S. Goodman, and Jack C. Eitniear. 2018. WEST INDIAN WHISTLING-DUCK FLOCK SIZE IN PUERTO RICO. Journal of Caribbean Ornithlogy www. jco.birdscaribbean.org Vol.31:23-25.
    Abstract
    West Indian Whistling-Ducks (Dendrocygna arborea), endemic to the West Indies, have been declining in recent decades. Although a scientifically accurate census has yet to be taken, it is estimated that there are about 100 individuals inhabiting Puerto Rico. We conducted ten 8-hour night observations at Laguna Cartagena National Wildlife Refuge between 19 January 2016 and 8 April 2016, resulting in an average of 131.9 birds (SE=4.5) with a high count of 153. West Indian Whistling-Ducks used the lagoon at night with the average arriving flock size being 4.65 (SE=0.6). The ducks approached from the West 2–67 minutes after sunset and departed to the West before sunrise. It is likely that the West Indian Whistling-Ducks are spending their days roosting in the mangroves of Refugio de Aves de Boquerón and their nights feeding at Laguna Cartagena National Wildlife Refuge. Our counts indicate that the population of West Indian Whistling-Ducks in Puerto Rico is larger than previously estimated. rnal of Caribbean

  2. In the last proposal to downlist the species, several members of the West Indian Whistling-Duck Working Group (one of BirdsCaribbean’s Working Groups) provided extensive comments on why we believed, based on the evidence, that changing the duck’s status to Near Threatened was not warranted or justified. Could you please provide a link to this past discussion or post the comments here.

    Nothing has changed since the last proposal to downlist the species, and in fact anecdotal evidence suggests that numbers are lower in some islands in recent years, due in part to severe drought but also likely habitat destruction and degradation and possibly other threats like hunting and invasive species.

    In the Caribbean, we continue to battle every day to save vital wetlands from being destroyed for development. The region also faced several devastating hurricanes in 2017, from which wetland habitats and birds are still struggling to recover. We still lack data from sound surveys in most islands (Cuba, Jamaica, etc.) assessing the population size.

    In the absence of valid survey data and continued threats, down listing the species is not advised. As of now, the WIWD’s presence in some countries helps with efforts to save wetlands and mangroves from destruction. Many wetlands in a number of countries would lose their status as IBAs as the presence of the WIWD is what triggered their designation. It would be a shame to lose all these IBAs and also risk increasing threats to the duck (and its mangrove/wetland habitats) because it no longer has Threatened status. We should not change the duck’s status without solid data supporting the decision to do so.

    • Red List Team (BirdLife International) says:

      Thank you very much for your comment. Could you please share the anecdotal evidence showing that the species has declined on some islands? This would greatly help us to ensure an adequate and appropriate assessment of the species’ Red List status.

  3. Rob Martin (BirdLife International) says:

    Here is the link to the previous discussion on the species: https://globally-threatened-bird-forums.birdlife.org/2014/08/west-indian-whistling-duck-dendrocygna-arborea-request-for-information/

    The current criterion still does not appear to be satisfied, as outlined in both that discussion and in the topic above, hence listing the species as Vulnerable requires either the species to meet the thresholds under a different criterion, or for the AOO to be accurately estimated and determined that it continues to meet thresholds for VU.

    Our preliminary assessment of a ‘maximum AOO’ indicates that this would not meet B2 thresholds, and in the absence of an AOO estimate calculated according to IUCN guidelines (IUCN 2012) the species cannot qualify under this criterion.

    However, if a continuing decline is inferred (our information on the population being stable or increasing is incorrect and it is suffering an ongoing population reduction), then the species might qualify under C2a(i), but that requires that the largest subpopulation numbers fewer than 1,000 mature individuals.

    Questions to answer to maintain Vulnerable status:

    Q.1. Is there a continuing decline? If no (as we currently believe), accept proposal as above (NT).
    If yes:
    Q.2. Does the rate of decline exceed 30% in 15.9 years? If yes, VU under A.
    If no:
    Q.3. Are there fewer than 1,000 mature individuals in the largest subpopulation?
    If yes, VU under C2a(i).
    If no, accept proposal above (NT).

    If the species does not meet the thresholds, it cannot be listed higher than Near Threatened, as proposed.

    IUCN (2012) IUCN Red List Categories and Criteria: Version 3.1. Second edition. IUCN Species Survival Commission. IUCN, Gland, Switzerland and Cambridge, U.K. http://www.iucnredlist.org/technical-documents/categories-and-criteria.

  4. Criterion A:
    Population decline: while local populations have increased on some islands, these gains may unfortunately be temporary as has been shown over the last 10 years in Jamaica, where the population appears to declining catastrophically. A comprehensive survey is urgently needed but my observations suggest that numbers at major sites have declined. At Negril the numbers seen have dropped from more than 100 to fewer than 10. In Black River Upper Morass, which previously supported a major part of the population, I rarely see any, and haven’t seen more than one individual for several years. This pattern is repeated across the island.

    Criterion B: The revised estimated extent of occurrence seems very large. Does this reflect the total area of the islands or the size of available and suitable wetlands in its range? This species requires wetland habitat and all remaining wetlands in the Caribbean are severely threatened by climate change and development. As Lisa says, the threat of loss of habitat will be increased if the species is down listed.

    Criterion C: Population size: the upper estimate of the population reflects an interview survey with Cuban hunters rather than a systematic scientific survey. These results need to be verified before they are accepted as the basis for a change in status. The margin of error is potentially huge and the increases in other parts of the range are trivial in comparison. There is compelling anecdotal evidence from Jamaica that some populations are declining.

    In response to Rob Martin’s comments:
    Q1; is the population in decline: There is insufficient data to determine this. With both habitat extent and quality declining, and hunting pressure increasing in Jamaica, it seems difficult to assume that numbers generally are increasing.
    Q2: rate of decline: no data. this rate of decline is probably exceeded in Jamaica.
    Q3: That may depend on how you define sub-population, whether by island or wetland unit. All populations are fragmented and thus more vulnerable than may appear from the overall estimated population.

    I agree with Lisa Sorenson that downlisting of this species at this time is not appropriate.

    • Red List Team (BirdLife International) says:

      Thank you very much for your comment. As we pointed out above, the species cannot continue being listed as VU under the current criterion. Therefore, in order to continue qualifying as VU, it needs to meet the threshold for another criterion.
      Following IUCN Guidelines, the EOO was calculated as the “spatial spread of the areas currently occupied by the taxon” (please have a look at Chapter 4.9 in https://www.iucnredlist.org/resources/redlistguidelines). The EOO is not equivalent to the area of mapped range. Unless new information on the population size becomes available, the population size is NOT the basis for a potential change in Red List status. According to IUCN Guidelines, subpopulations are defined as “geographically or otherwise distinct groups in the population between which there is little demographic or genetic exchange (typically one successful migrant individual or gamete per year or less)”, so not necessarily as island or wetland unit (please have a look at Chapter 4.2 in https://www.iucnredlist.org/resources/redlistguidelines).

  5. Red List Team (BirdLife International) says:

    The following comment was kindly submitted by Stefan Bräger via email:

    Dear Redlistteam,

    I understand that you would like to initiate the downlisting of the West Indian Whistling-duck from Vulnerable to Near Threatened (https://globally-threatened-bird-forums.birdlife.org/2019/05/west-indian-whistling-duck-dendrocygna-arborea-revise-global-status/). On that web page you state: “The global population is estimated at 10,000-19,999 individuals (L. G. Sorenson in litt. 2007, L. Mugica in litt. 2011), which roughly equates to 6,000-15,000 mature individuals. The largest population of up to 14,000 individuals is found in Cuba (Acosta-Cruz and Mugica-Valdés in litt. 2006). A further 1,500 individuals occur in the Bahamas; 4,500 individuals are found on other islands. Overall, the estimate of the global population size is conservative; it may be revised upwards if more recent estimates become available.”

    According to the IUCN web site (https://www.iucnredlist.org/species/22679770/84497213), Dendrocygna arborea was last assessed on 01 October 2016, which begs the question what new information has surfaced in the meantime to motivate such a move. Almost all of the sources quoted on your web page (mentioned above) are considerably older. Therefore, I would suggest that any change in status should be based on recent, comprehensive and scientific evidence, please. An interview survey among hunters (e.g., in Cuba), for example, would probably not qualify as a scientific study, I believe. Therefore, I would like to suggest that IUCN postpones any downlisting of this species until “more recent estimates become available”.

    Secondly, according to your population estimates, approximately 70% of the world population lives on a single island, which equates to putting (almost) all your proverbial eggs into one basket. Perhaps more importantly, it sends a disastrous message to all those islands where the populations have been plummeting in recent years (such as Jamaica, for example). Overhunting in those countries would be understood as acceptable, if IUCN (and Birdlife) downlist the species at the same time.

    Besides this (slightly political) message, such a downlisting would contradict any precautionary approach in view of accelerated climate change and related habitat loss in the Caribbean. In such a hurricane-prone region, it appears to be common sense to keep viable populations on more than one island. And this does not even consider the possible existence of genetically differentiated populations on different islands, some of which would likely be relinquished or lost, if your intended downlisting went ahead.

    Therefore, I would strongly recommend NOT to downlist the status of the West Indian Whistling-duck from Vulnerable.

    Kind regards,

    Stefan Bräger, PhD

    • Red List Team (BirdLife International) says:

      Thank you very much for your comment. As we pointed out above, the species cannot continue being listed under the current criterion. The current criterion was applied incorrectly, hence this needs to be corrected as soon as possible.
      With regards to your points: No major new information has surfaced since, thus we need to base the assessment on the data available. Unfortunately, this is not much in the case of the WIWD, so we have to rely on assumptions and anecdotal evidence. We do not ignore any evidence that we know of, and we always use a precautionary approach. Therefore, our assessment is based on the assumption that the true population size is on the lower end of the estimate, i.e. 6,000 mature individuals. If you have new information regarding the population size, please let us know.
      BirdLife International is carrying out global assessments at the species level and we are obliged to follow the IUCN Categories and Criteria. In many cases, local population trends may differ from the global trend, however, national and regional entities are entitled to carry out regional assessments, which obviously might differ from the global assessment. The IUCN Red List Category is a measure of the global extinction risk of a species; conservation projects and hunting regulations do not need to be based on it.

  6. “It would be a shame to lose all these IBAs and also risk increasing threats to the duck (and its mangrove/wetland habitats) because it no longer has Threatened status.”

    While I agree the species should not be downlisted at this time the above statement is not a valid scientific reason to prevent downlisting. Listing status must purely be based on the species population status not conservation value.

  7. Red List Team (BirdLife International) says:

    We thank all contributors for their comments regarding the Red List assessment of this species. We appreciate the concerns raised in the discussion. Prior to making a final decision, we want to briefly compare the currently available data against the relevant criteria:
    Criterion A: While parts of the population certainly show signs of recovery, the species is dependent on active conservation measures, without which it would potentially qualify as threatened. Moreover, there is concern that future climate change and extreme weather events may negatively impact the species’s habitat availability. Therefore, using a very precautionary approach, we may suspect that the population is in decline and list the species as Near Threatened under Criteria A2cde+3c.
    Criterion C: The assessment is based on the assumption that the true population size is closer to the lower end of the estimate, i.e. 6,000 mature individuals. This meets the threshold for Criterion C. As outlined above, we can furthermore precautionarily suspect a population decline. With a suspected decline however, the species can at most be listed as Near Threatened under Criterion C. We do not have data on the subpopulation structure, but based on the spread of records (e.g. Libro Rojo de los Vertebrados de Cuba, eBird) it is highly unlikely that the subpopulations are small enough to approach the threshold for listing as threatened under Criterion C2. Therefore, based on our available data, the species may be listed as Least Concern under Criterion C.

  8. Red List Team (BirdLife International) says:

    Preliminary proposals
    Based on available information, our preliminary proposal for the 2019 Red List would be to list West Indian Whistling-duck as Near Threatened, approaching the threshold for listing as threatened under Criterion A2cde+3c.
    There is now a period for further comments until the final deadline in mid-July, after which the recommended categorisations will be put forward to IUCN.
    Please note that we will then only post final recommended categorisations on forum discussions where these differ from the initial proposal.
    The final 2019 Red List categories will be published on the BirdLife and IUCN websites in December, following further checking of information relevant to the assessments by both BirdLife and IUCN.

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