The title of this study says “grebes” [plural], but the story involves a single grebe [singular]. That single grebe does, as the title implies, have a single [one] leg:
“Ecological Constraints and Phenotypic Accommodation in One-legged Eared Grebes,” Joseph R. Jehl Jr., The Wilson Journal of Ornithology, 125(4), 2013, pp. 829-832. (Thanks to investigator Adrian Smith for bringing this to our attention.) The author, at the Division of Birds, U.S. National Museum of Natural History, Smithsonian Institution, Washington, DC, reports:
“An Eared Grebe (Podiceps nigricollis) that lost a leg in an accident increased muscle mass in its intact leg by 28%. This allowed it to forage, run along the surface to take flight, and survive for about a year before dying in a weather-induced downing. Its ultimate survival probably depended on the species’ predilection for hypersaline habitats, where passive invertebrates are abundant and can be captured easily on the surface without the need to dive. Similar phenotypic accommodation may have been realized in other similarly impaired Eared Grebes. However, it seems unlikely to be achieved in other grebe species, particularly fish-eating pursuit divers, which require two intact legs and feet for propulsion and underwater maneuverability.”