Their distinctive bright red bills are used like a knife to shuck bivalves, but oystercatchers are also reported to swallow whole limpets and regurgitate the shells in the form of pellets.
BNA and Howard & Moore recognize five subspecies. Those found in western South America are assigned to H. p. pitanay in which the white wing stripe is reduced and confined to the secondaries. However Clements and IOC recognizes only two subspecies, the widespread nominate race and a distinctive form confined to the Galapagos. Those authors consider the rest of the geographic variation to be clinal or a consequence of hybridization with other species.
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References:
Hockey, P., Kirwan, G.M. & Boesman, P. (2018). American Oystercatcher (Haematopus palliatus). 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/53751 on 13 January 2018).
Working Group, American Oystercatcher, Erica Nol and Robert C. Humphrey. 2012. American Oystercatcher (Haematopus palliatus), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA. https://doi.org/10.2173/bna.82