Campbell Teal (Anas nesiotis): revise global status?

BirdLife species factsheet for Campbell Teal

Anas nesiotis is endemic to New Zealand, where it had been confined to Dent Island, an offshore islet of Campbell Island, for many decades. Native to Campbell Island, brown rats Rattus norvegicus caused its disappearance from this island (Williams and Robertson 1996, Williams 2013a). It is likely that no more than 25 breeding pairs were present in 1998 (Gummer and Williams 1999). In 1999-2000, 24 captive-bred birds were released on Whenua Hou/Codfish Island to create an insurance population, and the population there expanded rapidly (Gummer and Williams 1999, Gummer 2006b, Williams 2013b). Following the successful eradication of Brown Rat Rattus norvegicus from Campbell Island, 159 birds were released there between 2004 and 2006 (Potter 2006, P. J. McClelland in litt. 2012).

A 2008 survey at Campbell Island, along with opportunistic observations of breeding and dispersal activity (P. J. McClelland in litt. 2008, 2010, 2011), suggested that the population size in 2012 was between 100 and 200 mature individuals and so the species is currently listed as Endangered under Criterion D.

Based on opportunistic observations, the population size is now suspected to be greater than 500 mature individuals and to possibly number 800-1,000 mature individuals (P. J. McClelland in litt. 2019). Hence, we are undertaking a review of the species’s Red List Category.

Our current information on the species’s conservation status will now be compared to all Red List Criteria.

Criterion A – The species’s generation length is estimated at 5.1 years (Bird et al. 2020)*, meaning that the species has a three-generation length period of 15 years.In 2004, the population size was suspected to be 49 mature individuals (BirdLife International 2004) and in 2006, the population size was suspected to be 48-100 mature individuals (BirdLife International 2006). Based on opportunistic observations, the population size is now suspected to be greater than 500 mature individuals and to possibly number 800-1,000 mature individuals (P. J. McClelland in litt. 2019). Comprehensive surveys have not been undertaken so population estimates are uncertain, but the increasing trend is considered to have a high level of certainty (P. J. McClelland in litt. 2020). There is no evidence to suggest that the population size will undergo a reduction within the next three generations. This does not approach the thresholds for listing the species as threatened under Criterion A. The species is therefore assessed as Least Concern under this criterion.

Criterion B – The species’s Extent of Occurrence (EOO) is to be 7,320 km2, based on a minimum convex polygon around Campbell Island, Dent Island and Whenua Hou. This meets the threshold for Vulnerable under Criterion B1.Based on a 4km2 grid placed over the area of mapped range, the species’s area of occupancy (AOO) must be smaller than 356 km2 and is considered to fall within the range 10-356 km2. This meets the threshold for Endangered under Criterion B2.To list the species as threatened on the Red List under Criterion B, two of conditions a-c must also be met.

Although the species occupies small islands that are separated by a large distance, it is not considered likely that more than half of its total area of occupancy is in habitat patches that are smaller than would be required to support a viable population. Therefore, the species is not considered to be severely fragmented according to the IUCN definition (IUCN Standards and Petitions Committee 2019). The main threat to the species is considered to be future introductions of invasive rat species. The introduction of rats to Campbell Island or Whenua Hou could lead to rapid declines and potentially the extirpation of a subpopulation. The species is therefore considered to have two locations. Condition (a) is therefore met at the level of Endangered. There is no evidence that the species’s population size, range size or habitat quality are undergoing a continuing decline. The species’s population size is increasing (Robertson et al. 2016, P. J. McClelland in litt. 2019). Condition (b) is therefore not met. There is no evidence that the species’s population or range size are undergoing extreme fluctuations. Condition (c) is therefore not met.

Although the species’s EOO falls beneath the threshold for listing the species as Vulnerable under Criterion B1 and the species’s AOO falls beneath the threshold for listing the species as Endangered under Criterion B2, only one of the three conditions is met. Therefore, the species is assessed as Near Threatened, approaching a listing as threatened under Criteria B1a+2a.

Criterion C – The species is secretive and no comprehensive or systematic surveys have been carried out, but based on opportunistic observations, the population size is suspected to be greater than 500 mature individuals and to possibly number 800-1,000 mature individuals (P. J. McClelland in litt. 2019). The species meets the population size threshold for listing as Endangered under Criterion C.

To list the species as threatened under Criterion C there must also be evidence that the species’s population size is undergoing a continuing decline, but there is no evidence to indicate this, as the population is increasing (Robertson et al. 2016, P. J. McClelland in litt. 2019). The species therefore qualifies as Least Concern under Criterion C.

Criterion D – Although the population size in 2012 was suspected to fall between 100 and 200 mature individuals, the population size is now suspected to be greater than 500 mature individuals and to possibly number 800-1,000 mature individuals (P. J. McClelland in litt. 2019). The species therefore qualifies as Vulnerable under Criterion D1.Given that the current population estimate is at least double the threshold for listing the species as Endangered (250 mature individuals), and that the 2016 national assessment of the conservation status of New Zealand’s birds placed the population size at 250–1000 mature individuals, the species is likely to have qualified for Vulnerable under Criterion D1 for at least five years.

As described under Criterion B, the species has a very small number of locations. It could be driven to Critically Endangered in a short period due to a threat such as the introduction of rats, a severe weather event or an oil spill. The species therefore qualifies as Vulnerable under Criterion D2.

Criterion E – To the best of our knowledge no quantitative assessment of the probability of extinction has been conducted for this species, and so it cannot be assessed against this criterion.

Based on the above assessment, it is proposed to list Campbell Teal (Anas nesiotis) as Vulnerable under Criteria D1+2. We welcome any comments to the proposed listing. Information is particularly requested on the species’s population size throughout the period 2015-2020. Please note that species should only be downlisted to a lower category of threat on the IUCN Red List when they have not qualified for the higher category for at least five years. Therefore, if evidence suggests that the species’s population size has fallen beneath 250 mature individuals during the period 2015-2020, the species may be retained as Endangered under Criterion D.

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. By submitting a comment, you confirm that you agree to the Comment Policy.

*Bird generation lengths are estimated using the methodology of Bird et al. (2020), as applied to parameter values updated for use in each IUCN Red List for birds reassessment cycle. Values used for the current assessment are available on request. We encourage people to contact us with additional or improved values for the following parameters; adult survival (true survival accounting for dispersal derived from an apparently stable population); mean age at first breeding; and maximum longevity (i.e. the biological maximum, hence values from captive individuals are acceptable).

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

Bird, J. P., Martin, R., Akçakaya, H. R., Gilroy, J., Burfield, I. J., Garnett, S. G., Symes, A., Taylor, J., Şekercioğlu, Ç. H. and Butchart, S. H. M. 2020. Generation lengths of the world’s birds and their implications for extinction risk. Conservation Biology online first view.

BirdLife International (2004) Species factsheet: Anas nesiotis.

BirdLife International (2006) Species factsheet: Anas nesiotis.

Gummer, H. 2006b. Flightless ducks return home. World Birdwatch 28: 13-16.

Gummer, H.; Williams, M. 1999. Campbell Island Teal: conservation update. Wildfowl 50: 133-138.

IUCN Standards and Petitions Committee. 2019. Guidelines for Using the IUCN Red List Categories and Criteria. Version 14. Prepared by the Standards and Petitions Committee. Downloadable from http://www.iucnredlist.org/documents/RedListGuidelines.pdf  

Potter, J. 2006. Return of teal to Campbell Island. Oryx 40: 137.

Robertson, H.A., Baird, K., Dowding, J.E., Elliott, G.P., Hitchmough, R.A., Miskelly, C.M., McArthur, N., O’Donnell, C.F.J., Sagar, P.M., Scofield, R.P. and Taylor, G.A. 2017. Conservation status of New Zealand birds, 2016. New Zealand Threat Classification Series 19. Department of Conservation, Wellington.

Williams, M. 2013b. Campbell Island Teal: Has re-establishment been achieved? TWSG News 16: 26-27.

Williams, M.J. 2013a. Campbell Island teal. In Miskelly, C.M. (ed.) New Zealand Birds Online. Available at: www.nzbirdsonline.org.nz.

Williams, M.; Robertson, C. J. R. 1996. The Campbell Island Teal Anas aucklandica nesiotis: history and review. Wildfowl 47: 134-165.

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4 Responses to Campbell Teal (Anas nesiotis): revise global status?

  1. Glyn Young says:

    The story of the Campbell teal’s recovery is testament to a remarkable project to save this little known duck. Many different elements to the project should be highlighted including captive breeding and invasive mammal eradication in some pretty hard to reach islands. I support the change of status to Vulnerable and thank all involved in this success. The species is still highly vulnerable to reinvasion by non-native mammals, is never going to disperse much without assistance and should be monitored closely for the foreseeable future.

  2. Pete McClelland says:

    Criterion A –
    While there is no evidence to back this up I would suggest that after 14 years (Campbell) and over 20 years (Whenua Hou) with a significant founder population, a relatively high reproductive rate and in known suitable habitat that the three sub populations are likely to be at or close to capacity ie are not increasing. Providing the islands are kept predator free, and no new pathogens occur, there is no reason to believe that either population will decline. The exception to this would be if the decision was made to remove the population from Whenua Hou (refer below). However even then that would be a one off decline, albeit a very significant one, and not continual.

    Criterion B –
    The EOO given (7320km2) is totally misleading as the bird is primarily terrestrial so only the land area is relevant ie Campbell 11300h and Whenua Hou 1396ha and Dent 26ha, total 12722ha = 128km2 well below the 356km2 required to not met this criteria.
    All of its AOO, with the possible exception of Dent, ie Campbell and Whenua Hou have shown themselves to be more than capable of supporting viable, self-sustaining populations in the long term.
    While there are currently 2 widely separated viable subpopulations, which means that a single catastrophic event would not put the species at risk, there are currently discussions concerning actively removing them from Whenua Hou as this was only ever intended as a short term holding site and their presence there precludes the reintroduction of Brown teal (Anas chlorotis) not only to Whenua Hou but also possibly to Rakiura/ Stewart Island as this is with in known flying range and would risk hybridisation of the two species. Brown teal are currently classified as recovering and there are active discussions about reintroducing them to Rakiura as part of a large scale predator eradication/ island restoration programme. Also the Campbell Island teal on Whenua Hou have been found to be impacting seabirds by killing of chicks in burrows. This raises a concern that they may also pose a risk to kakapo chicks (critically endangered) in similar situations.

    Criterion C –
    While not detailed surveys have been undertaken based largely on opportunistic observations it is very likely that the total population exceeds 500 mature adults over the two main sites but the 800- 1000 is an optimistic extrapolation across habitat types. While there is no evidence to back this up I would suggest that after 14 years (20+ for Whenua Hou), with a significant founder population, a relatively high reproductive rate and on known suitable habitat that the three sub populations are likely to be at or close to capacity ie are not increasing. Providing the islands are kept predator free, and no new pathogens occur, there is no reason to believe that either population will decline. The exception to this would be if the decision was made to remove the population form Whenua Hou as stated above. However even then that would be a one off dedcline, albeit a very significant one, and not continual.

    Criterion D –
    There is little doubt that with the three current subpopulations the total population well exceeds the 250 mature individuals. The concern would be if they were to be removed from Whenua Hou but even then it is believed that the Campbell and Dent populations alone would exceed 250 mature individuals so as stated unless impacted by a catastrophic event such as introduced predators or disease it would still qualify as vulnerable under criteria D2.

    Criterion E –
    Agreed – the major risk of extinction would be from a catastrophic event such as the introduction of invasive predators or disease which can not be predicted.

  3. Red List Team (BirdLife International) says:

    Many thanks to everyone who has contributed to this discussion. We greatly appreciate the time and effort invested by so many people in commenting. The window for consultation is now closed. We will analyse and interpret the new information and post a preliminary decision on this species’s Red List status on this page in early July.

    Thank you once again,
    BirdLife Red List Team

  4. Red List Team (BirdLife International) says:

    Preliminary proposal

    Thank you for the comments on this proposal. We agree that the extensive conservation efforts that have been made to conserve this species are to be applauded.

    We have noted that the population size may now be stabilising. Although it may seem counter-intuitive, it is correct according to IUCN Guidelines to include the area of sea within the extent of occurrence (EOO) estimate. This is because the EOO is intended to represent the spatial spread of the species’s distribution, rather than the area occupied. For example, a species that occurs on two islands that are close together may be more at risk than a species that is on two islands that are far apart, since a threat may be less likely to affect both islands if they are further apart. If the species is removed from Whenua Hou, the assessment should be updated. However, the species still would not qualify as threatened under Criterion B in the absence of a continuing decline in population size, range size or habitat extent/quality.

    Based on available information, our preliminary proposal for the 2020 Red List would be to list Campbell Teal as Vulnerable under Criterion D2 .

    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 those in the initial proposal.

    The final 2020 Red List categories will be published on the BirdLife and IUCN websites in December 2020 or January 2021, following further checking of information relevant to the assessments by both BirdLife and IUCN.

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