GALLON JUG, Belize -- At the Chan Chich Lodge, a nature resort tucked amid Mayan ruins here in the thick forests of this Central American nation, a handful of affluent Americans bend forward, squinting to detect the movement of birds flitting silently in the moist, all-encompassing green.
After repeatedly playing a tape of one bird's call, standing motionless for minutes and chirping expertly himself in vain, Drew Thate, the party's guide, issues a summons to move on.
"White-breasted wood wren 10, people nothing," he says, drawing a chuckle from the bird watchers, who had each paid thousands of dollars for that frustration, as well as glimpses of exotic birds like the Aracari toucan and masked tityra.
With increasing numbers of affluent foreigners willing to spend freely to partake in the boom of what is often called eco-tourism, Belize, the region's smallest nation, has been rushing to get onto tourist circuit that has long ignored it by marketing its mostly pristine environment.
With 250 varieties of orchid, the hemisphere's longest barrier reef and fauna ranging from the endangered jaguar to a dazzling variety of birds, environmentalists say Belize is as richly endowed by nature as any similarly sized place on earth.
Already, great chunks of this sparsely populated, Massachusetts-sized country consist of parks and protected lands. At 200,000, the number of tourist visits in Belize has doubled in the last four years, slightly outstripping the number of inhabitants.
But even as plans to expand nature tourism proceed, concerns have been raised that the marketing of Belize as one of the world's least spoiled lands may end up undoing the very nature that is being sold to avid outsiders.
At the Chan Chich Lodge, biologists laud the care taken to preserve the surroundings. Hunting and fishing, for example, are prohibited. The number of guests is strictly limited by the availability of only 12 thatched-roofed cabanas. Guides accompany visitors on hikes over miles of jungle trails that wend their way around 1,500-year-old Mayan burial mounds.
But elsewhere in the country's interior, the success of places like Chan Chich has drawn less conscientious imitators.
Along the wilds of the Macal River, another nature lodge that is given high marks for the care it has shown for the surrounding environment has seen more than a dozen copycat lodges sprout up in the last couple of years to offer hikes and canoe rides amid a greenery of Amazonian splendor.
To accommodate urban tourists, some have razed undergrowth down to the riverbanks, leading to rapid soil erosion and damage to the aquatic life.
But for many, the best example of the environmental degradation in Belize is the development of its coast. Well before the advent of eco-tourism, Belize's extraordinary reefs made it a favorite destination for divers, and sprawling developments were built on the most popular keys. Some of the favorite reefs began to die.
Belize has responded to the reef damage by suspending new construction on the keys pending an environmental impact study and is considering measures like raising fees for divers and limiting their numbers.
"One thing we have learned is that the principles for eco-tourism are not firmly established yet," said the minister of tourism, Glen D. Godfrey. "You often don't know when you are going over the limit until after the fact."
Arnold Brown, a director of the Programme for Belize, a group founded to conserve and manage 202,000 acres of wilderness in the northwestern corner of the country, is itself planning nature tourism activities for its lands, as well as small-scale, experimental logging and agricultural projects that it hopes will pay for its conservation and serve as a model elsewhere in the country.
"It has been helpful that Belize is aware that much of the world has its eyes on what is happening here," said Bruce W. Miller, a research fellow with Wildlife Conservation International, a branch the New York Zoological Society.
"If we can't find a sensible way to both use and protect these resources in a sparsely populated place like Belize, where much of the forest is intact, it's unlikely we can do it anywhere."