Canon PowerShot SX60 HS.
Digiscoped with Panasonic DMC-LX5 | Nikon FieldScope 3 | 30X WA | hand-held (no adapter)
This close relative of the Mallard is endemic to Hawaii where it remains endangered. By 1962 they numbered fewer than 500 birds. Their decline has been attributed to a combination of wetland habitat loss, hunting, Mongoose predation and hybridization with feral Mallards which escaped from commercial farms on Oahu. The current total population is estimated at about 2000 birds. The healthiest population is on Kauai where it is fairly widespread although much reduced from historical numbers. We only saw a few. This species is smaller and darker than female or eclipse male Mallards from which they also differ in having a mostly dark bill with olive tones. Males lack the Mallard's curled outer tail-feathers. Hawaiian Duck undertail coverts are mottled and their flanks are usually more boldly patterned. When visible the speculum is greenish-blue rather than deep blue. Hybrids can be difficult to identify but are reported to be rare on Kauai.
References:
BirdLife International 2017. Anas wyvilliana (amended version of 2016 assessment). The IUCN Red List of Threatened Species 2017: e.T22680199A112386802. https://dx.doi.org/10.2305/IUCN.UK.2017-1.RLTS.T22680199A112386802.en. Downloaded on 01 February 2020.
Engilis Jr., A., K. J. Uyehara, and J. G. Giffin (2002). Hawaiian Duck (Anas wyvilliana), version 2.0. In The Birds of North America (A. F. Poole and F. B. Gill, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bna.694
del Hoyo, J., Collar, N. & Kirwan, G.M. (2020). Hawaiian Duck (Anas wyvilliana). 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 https://www.hbw.com/node/467121 on 1 February 2020).
Pratt, H.D., Bruner, P., and Berrett, D.G. (1987) A Field Guide to the Birds of Hawaii and the Tropical Pacific. Princeton University Press.
Pyle, R.L., and P. Pyle. 2017. The Birds of the Hawaiian Islands: Occurrence, History, Distribution, and Status. B.P. Bishop Museum, Honolulu, HI, U.S.A. Version 2 (1 January 2017) http://hbs.bishopmuseum.org/birds/rlp-monograph/