The Extinction of a Species
LaBastille, A., 1990. Mama Poc: An Ecologist's Account of the Extinction of a Species.
An American scientist, Anne LaBastille, came to Guatemala in 1960 to study the giant grebe, a bird that apparently lived only on Lake Atitlan, in the highlands of western Guatemala. She counted 200 birds, a number close to that known from the last count in 1936. The population seemed to be stable, but she was so fascinated by the rarity of the bird that she planned to return for further study. Because of her interest in these birds, the locals called her “Mama Poc” (poc is the Mayan name for the grebe).
Pairs of grebes claim and defend a territory requiring dense, wide reed beds along 300 feet or more of shoreline. This species builds a giant nest in the reeds, 18 inches wide on a base 36 inches deep.
Both parents care for grebe chicks for their first three months. During that time the mortality is about 50 percent. As the grebes mature and go out on their own, their death rate increases. The chicks eat insects, crustaceans, and small fish.
In 1958 a new fish, black bass, was introduced into Lake Atitlan. Making this highly prized fish available was seen as a way to attract tourism and boost the local economy. This was done at the suggestion of Pan American World Airways and with the approval of the local tourism-promotion board. The area around Lake Atitlan, a national park since 1955, was mostly unknown to the world, and Guatemala was eager to become a prime destination for tourists.
By 1960, black bass were caught by the local fishermen, but with difficulty since the local indigenous people (the Maya) couldn't afford scuba gear or the type of sturdy fishing tackle that's best suited for catching black bass. It's unlikely that they would use scuba gear if they had it, since few know how to swim.
Upon her return in 1965, LaBastille searched the reed beds along the shore for months. She found only 80 birds. The local human population had harvested many of the reeds, leaving smaller areas for the grebes to nest in. In addition, the young grebes were unable to eat the black bass because the young black bass are so spiny that they are difficult to swallow. The young grebes had fewer edible food sources because about two-thirds of the native fish species were also now gone from the lake. The introduced black bass were out-competing the native fish for resources.
This loss of native fish impacted the local human population as well. Whereas a local fisherman could once catch 20 to 50 pounds of fish per day, the catch now was a tenth of that amount. The crab catch for the local fishermen has also declined considerably, now at one-third of former levels. Overall, fishing as a livelihood was possible for one third as many families as before. In the meantime, black bass weighing 10 to 20 pounds were being caught by spear fishing tourists.
By the late 1960s, the Guatemalan government had taken three steps to protect the giant grebe, 1) a part-time game warden was hired to enforce laws against killing animals in the national park, 2) new laws were passed that prohibited cutting of reeds at the shore between May and August, and 3) a wildlife refuge (the first in the nation) was established in a secluded five-acre bay. The refuge included a barricade that kept the black bass from entering the grebe nesting areas.
With the black bass excluded by a stone barricade, LaBastille and the game warden released two pairs of giant grebes and 6,000 young native fish in the refuge. The population of the grebe recovered from 80 birds in 1965 to 232 birds in 1975.
In 1976 a massive earthquake struck Guatemala. The lakebed was fractured in such a way that water began to slowly leak from it. The water level dropped four feet in 2 years, 12 feet in 4 years, 29 feet in 18 years. Since the lake occupies a steep-sided crater, the immediate effect was the reduction of the regions of shallow water at the lake margins. As the grebe refuge dried up, the birds were released.
By 1980, the human population around the lake had increased to over twice its 1950 level. Interest in the lake as a place for non-Mayans to visit and live also increased. A three-tower, 16-story condominium was built on the shore. Speedboats and skiers crowded the lake on weekends. By this time there were 350 weekend cottages and villas, compared to 28 in 1960, built on newly cleared land along the shore. Only six and a half miles of reed bed (suitable for nesting grebes) remained, representing a 57% reduction.
Despite the human population pressures, there were no controls on the quality of the environment. Villages, hotels, and homes dumped raw sewage into the lake; pesticides and chemical fertilizers were used at levels previously unknown. The native women began to use detergents instead of the traditional homemade soaps while doing laundry in the lake.
Civil strife in Guatemala accelerated in the 1980s, making it unsafe to monitor the grebe population. In 1982, the only game warden patrolling the lake was murdered. By 1984, only about 20% of the original reed beds remained. The population of grebes declined and never recovered.
The final grebe data that Anne LaBastille collected between 1980 and 1991:
1980 - 130 birds
1982 - 80 birds
1985 - 56 birds
1989 - 4 birds
1991 - None could be found, species declared extinct.
This species extinction demonstrates all five human causes of extinction:
Habitat destruction: reed cutting
Invasive/introduced species: black bass
Population Growth: human
Pollution: raw sewage, pesticides, fertilizers and detergents
Over harvesting: cutting the reeds