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.
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.