Status of the Endemic Atitlan Grebe of Guatemala: Is It Extinct?

Abstract

Efforts to determine the factors responsible for the long-term population decline of the Atitlan Grebe (Podilymbus gigas), a species restricted to Lake Atitlan in Guatemala, led to the discovery that the only Podilymbus species present on Lake Atitlin in 1986-1987 was the Pied-billed Grebe (P. podiceps). Podilymbus gigas is similar to P. podiceps in color and form but is almost twice the weight, and is reported to be flightless. All Podilymbus grebes at Lake Atitlin in 1986-1987 appeared to be the same size, and the body masses and bill measurements of six captured grebes were within the range of P. podiceps, but not that of P. gigas. Grebe eggs measured at both Lake Atitlin and Laguna del Pino, another Guatemalan lake, were similar to each other and to eggs ofP. podiceps from North America. The territorial calls of male Podilymbus grebes recorded at Lake Atitlan, Laguna del Pino and West Toqua Lake in Minnesota did not differ significantly. It thus appears that P. gigas no longer occurs on Lake Atitlin and has been replaced, perhaps through competition or hybridization, by P. podiceps.