Atitlan Grebe Podilymbus gigas. Original artwork from A Gap in Nature.
Watercolour and gouache on Arches paper, 305 x 690mm, framed, signed and dated by artist.
Last Record. 1989. Distribution: Lake Atitlan, Guatemala.
There is a convention in biology that one must wait fifty years after a last sighting before a species is proclaimed extinct. Some species, however, have such restricted distributions, or are so well known, that their extinction is evident soon after a last sighting is made. Such was the case with the Atitlan grebe, a giant, nearly flightless water bird that inhabited a single place, the 360-metre-deep Lake Atitlan in the Guatemalan highlands. Known to the local inhabitants as mama poc, the grebe had presumably cruised the lake's waters since the species had evolved before the last ice age.
Until about 1965 it enjoyed a relatively stable population of around 800. Soon thereafter, however, a series of changes occurred which disadvantaged the birds. Both small- and large-mouth bass were introduced into the lake in 1958, and these voracious predators greatly reduced the crab and fish populations upon which the grebe depended. By 1975 the grebe population had fallen to around 210 individuals, and a conservation program was instituted to protect the species by legislation, community education and habitat preservation. The campaign was inadequate, however, for along with the bass other changes were afoot that would destroy the species. The water level was falling, and would drop over six metres in the thirty -five years after 1965. Reed-cutters were destroying valuable habitat and the lake was invaded by the related and widespread common pied-billed grebe.
Researchers surveyed the grebe population by playing a recording of the call of the male at night during the breeding season. Any male hearing the call of another male would respond, giving an accurate estimate of the number of breeding pairs. The trouble was, the calls of the pied-billed and giant grebes were very similar, and the researchers did not realise that a second species had invaded the lake. By the late 1970s they were predicting a resurgence in numbers of the giant grebe, until one day they approached some -and, to their horror, they saw the birds fly away. They then realised that they had been counting not the flightless giant grebe, but its smaller, flighted pied-billed relative.
The pied-billed grebe found the degraded lake much to its liking, and by the mid-1980s was breeding year-round and producing multiple broods. It may have hybridised with the giant grebe, thus reducing its breeding success, or may have simply outcompeted it. By 1989 just two pairs of giant grebe inhabited the lake, and none have been seen since.