Atitlan Grebe Podilymbus gigas Scientific name definitions

Atitlan Grebe is an extinct species that was formerly endemic to Lago de Atitlan in Guatemala. Curiously, this bird was like a large version of Pied-billed Grebe (Podilymbus podiceps), but had very reduced wings and was flightless. Introduced bass led to a decline in the fish and crabs that served as food for the grebes, and lowered water levels in the lake associated with a large earthquake in 1976 further hurt the species. While never abundant, the species declined from 200 individuals in the 1960s until no more were found after 1989 when the species sadly became extinct.

42–52·5 cm; c. 500–800 g. Large, drab-looking grebe with very robust head and bill. Close view of adult  |Several views, including close-up |Swimming adult  very like that of P. podiceps, mostly dark grey-brown, darker on crown, hindneck and upperparts, blacker on chin and throat; wings reduced (rendering it almost flightless); chest finely streaked silvery, with some whitish visible on flanks, abdomen white spotted grey-brown, undertail-coverts white; iris brown or dark brown, narrow whitish orbital ring of bare skin; bill whitish, often with pale yellow tinge, and usually greyer on distal third, separated by conspicuous blackish vertical band; legs slate-grey or brownish. Non-breeding plumage paler, with less black on head, more greyish mottling on underparts, bill duller and browner. Sexes similar. Distinguished from similar P. podiceps by notably larger size, more robust head and proportionately larger bill, especially thicker base. Juvenile similar to non-breeding adult, with pale stripes on sides of head and neck.

Always confined to a single lake, where population never exceeded c. 400 individuals. Introduction of large predatory fish greatly reduced its population, this was exacerbated by egg-collecting, poaching and reed-harvesting during breeding season, and later by urbanization and further habitat destruction. Hybridization with P. podiceps may have played a part in the final extinction of P. gigas, which occurred at some time between 1983 and 1986 (1 LaBastille, A. (1990). Mama Poc: An Ecologist’s Account of the Extinction of a Species. W.W. Norton & Co., New York. Close ).

L Atitlán, in SW Guatemala.

L Atitlán, at c. 1560 m: near-shore waters with thick emergent vegetation, especially beds of rushes, reeds and cat-tails.

Sedentary; practically flightless.

Mainly fish up to 13 cm long; also insects, especially dragonfly nymphs (Odonata), snails, and the native crab species Potamocarcinus guatemalensis. Powerful bill and strong muscles of head, neck and bill were adaptations for capturing of this crab, which was once abundant in lake and was probably main prey item. Prey caught by diving to considerable depths, for which large size important; average dive duration 34·9 seconds for males and 27·1 for females, with respective maxima of 90 and 52 seconds. Juveniles recorded as foraging at surface, picking corydaline fly larvae (hellgrammites) and aphids (Aphidoidea) off reeds.

Song, usually  in early and late parts of day, also at night, as duet, a fast chatter and loud “kut-kut-kuh-kuh-kuh”, turning into disyllabic “puk-puk”, and ending with 2 or 3 braying “iyaw iyaw” notes. Loud “kuh kuh” as contact; alarm a loud “bok”.

Breeding started in Mar, with peak laying in Apr; nesting possibly throughout year on occasions. Solitary. Nest a large, compact floating platform of aquatic vegetation always well anchored to submerged plants. Clutch 1–5 eggs, average 2·9; no information on incubation period; chicks   had blackish-grey down with white and grey stripes, paler on abdomen; independent at 10–12 weeks of age. Estimated 1·36 young per brood reached independence, implying survival rate of c. 47%.

EXTINCT. CITES I. This species was always confined to a single lake, 130 km² in extent, in highlands of S Guatemala. Maximum estimate of global population c. 400 birds, in 1929. Approximately 100 pairs counted in 1960, but introduction of largemouth bass (Micropterus salmoides) into L Atitlán in 1958–1960 almost certainly responsible for subsequent slump to c. 80 individuals in 1965, the bass competing with this grebe for food and taking its chicks. Several protective measures were then undertaken, including employing of guards to prevent illegal egg theft and poaching of waterbirds (banned since 1959), and prohibition of reed-collecting (for local weaving industry) between May and Aug, reeds being essential for the grebes for nesting and shelter; in addition, a 2-ha reserve was established in 1968 and provided effective protection for two pairs of these grebes (although the lake had been declared a national park in 1959, local people were quite unaware of the fact), and in 1969 conservationists succeeded in halting a proposed hydro-electric scheme which would have irreversibly changed the lake’s condition. These measures, and perhaps also some adaptation by grebes to presence of bass, led to a spectacular recovery, with 232 birds counted in 1975. Unfortunately, intensive urbanization of the lake’s shores had begun in 1960s and 1970s, aggravated by earthquake in 1976 as the water level dropped by c. 5 m, and this resulted ultimately in the destruction of the shore area and its vegetation. In 1980, only 130 grebes counted and suitable breeding habitat reckoned to have decreased by c. 60%; at same time exploitation of reeds and hunting became uncontrolled, exacerbated by murder of government game warden for the national park during political unrest of 1982, and combination of all factors drove the species into irreversible decline. Only 30 individuals were found in 1983, and by 1986, when P. podiceps was observed on the lake, the present species was extinct. Uncertain whether P. podiceps responsible for its disappearance through competition or hybridization; it may simply have replaced it, when extinction imminent. The demise of this distinctive grebe has been well documented (2 LaBastille, A. (1990). Mama Poc: an ecologist's account of the extinction of a species. Norton, New York. Close , 3 LaBastille, A. (1990). And now they are gone. Int. Wildl. 20(4): 19-23. Close , 4 LaBastille, A. (1992). The Giant Grebes of Atitlán. A Chronicle of Extinction. Living Bird Quarterly 11(1): 10-15. Close ).