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Sometimes recognised as a separate species, A. carolinensis2; taxonomy still in much of debate as genetically, this subspecies seems to be more closely related to Andean Teal and Yellow-billed Teal than to nominate A. c. crecca.
Carboneras, C., Christie, D.A. & Kirwan, G.M. (2019). Common Teal (Anas crecca). 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/52868 on 24 April 2019).
Johnson, K. (1995). Green-winged Teal (Anas crecca), 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.193