We found a pair of these endangered flightless teal swimming in a kelp bed (Durvillea antarctica). One of the world's rarest ducks, the male showing a hint of green on its head. This species was thought to be extinct until a tiny population was discovered on nearby Dent Island in 1973. 105 captive bred teal, all descended from a single female, were reintroduced to Campbell Island after rats were eradicated in 2003. The current wild population of about 70-90 birds is a mix of released captives and a few natural colonizers from Dent Island. This duck remains critically endangered.
Its closest relative is the vulnerable flightless Auckland Islands Teal (A. aucklandica). The Campbell Islands Teal is smaller but has a more prominent eyering and the male usually has more extensive green on its head. Both are related to the similar Brown Teal (A. chlorotis) of the main islands which is capable of flight.
All three were formerly treated as a single species. However, they are genetically distinct and are now usually treated as separate species for conservation purposes, or following a phylogenetic species concept. (Daugherty et al. 1999, Kennedy and Spencer 2000). However H&M4 lump all three under the name "New Zealand Teal" presumably to preserve their former status under the biological species concept and a conviction that conservation concerns should not drive taxonomy. Canon PowerShot SX50 HS.
References:
Daugherty, C.H., M. Williams, and J.M. Hay. 1999. Genetic differentiation, taxonomy and conservation of Australasian teals Anas spp. Bird Conservation International 9:29-42.
https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0959270900003324
del Hoyo, J., Collar, N. & Kirwan, G.M. (2017). Campbell Teal (Anas nesiotis). 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/467125 on 6 March 2017).
Kennedy, M. & H.G. Spencer 2000. Phylogeny, biogeography and taxonomy of Australasian teals. Auk 117(1):154-163.
https://sora.unm.edu/sites/default/files/journals/auk/v117n01/p00154-p00163.pdf
Marchant, S. & Higgins, P.J. (coordinating editors) 1990. Handbook of Australian, New Zealand & Antarctic Birds. Volume 1, Ratites to ducks. Melbourne, Oxford University Press.
Shirihai, H. (2002) A Complete Guide to Antarctic Wildlife. The Birds and Marine Mammals of the Antarctic Continent and the Southern Ocean. Princeton University Press: Princeton & Oxford.
Williams, M.J. 2013. Campbell Island teal. In Miskelly, C.M. (ed.) New Zealand Birds Online. www.nzbirdsonline.org.nz