Bird lovers and scientists have always shown a special interest in hummingbirds. The smallest and hardest-working of all birds, members of the family Trochilidae are found only in the Americas.

They were a favorite subject of the 19th century American artist and naturalist, John James Audubon, who painted a group of ruby-throated hummingbirds for his classic reference work, The Birds of North America. Audubon described the tiny bird as "a glittery fragment of the rainbow." And ornithologist Frank M. Chapman, in his Handbook of Birds of North America, wrote that "the Ruby-throat needs no song. Its beauty gives it distinction, and its wings make music."

Despite the hummingbird's popularity, however, its survival in many parts of the Americas is being threatened by human development.

Watching a hummingbird can inspire awe. Its size and beauty are part of its charm. Then there's the way it flies.

"We look at the average bird and we know how it flies. But we look at the hummingbird and it hovers in mid-air," says Ross Hawkins, who heads the Hummingbird Society, a group dedicated to protecting hummingbirds. "It flies right up to us. It flies backward, sideways, and even flies upside down for a period of time. And it makes us think of a combination of a helicopter and a fighter jet!"

Yet the hummingbird's most important role in nature often goes unnoticed that of a pollinator of many flowers. Some flowers are actually shaped in a way that makes their nectar and pollen accessible only to hummingbirds and to only one species of the bird.

"If you go down to South America, the Swordbill Hummingbird pollinates the Datura, which has a 13-centimeter long blossom that hangs downward. Only the Swordbill hummingbird can come underneath the flower and put his seven to eight-centimeter-long bill up inside, and with his tongue go even farther and pollinate that flower," Ross Hawkins explains. "No other insect or bird is known to pollinate that flower, so it would simply die if that bird becomes extinct."

Mr. Hawkins says these plants actually evolved to suit the hummingbird and vice versa.

"There is a Hermit [hummingbird] in South America whose bill is extremely curved," he says. "And there is a Helconia whose flower is shaped exactly to match that curve, and that's another one of the flowers that can only be pollinated by that particular species of hummingbird."

There are 328 species of hummingbirds that live on earth, but only in the Western Hemisphere. About 140 species can be found in the South American nation of Ecuador. The hummingbird is a migratory species. Tens of thousands of birds fly between the United States and Mexico or Central America every year. Ross Hawkins notes that these tiny birds can live in almost any terrain, and Ecuador's environmental diversity is ideal.

"It has a wide diversity of habitat. It has hummingbirds at 14,000 feet (4500 meters) high in the Andes Mountains," he says. "It has hummingbirds in the lowland tropical forests. It has hummingbirds in every altitude in between. It's that range of habitats that makes it and Colombia the two richest countries in the world for hummingbird species."

The United States claims 16 hummingbird species. But only one breeds east of the Mississippi River - the Ruby-throated Hummingbird.

At a lecture and slide show at Washington College in Chestertown, Maryland, Mr. Hawkins addresses a crowd of students and bird watchers. Among them are Pat McDonald and Alexis Stapanon, who find the Ruby-throated Hummingbird a remarkable creature.

"This summer I was watering my lawn, and a hummingbird came in the spray from the hose and just for about 30 seconds took a nice little shower and then flew away," Ms. McDonald said. "I think they're just so precious and interesting."

"I think how small they are and how they move their wings - it's just amazing to watch them," said Ms. Stapanon.

The hummingbird's tiny size invites many predators - such as cats, spiders, bigger birds, praying mantises and even large fish, which mistake them for moths. But the greatest threat is the destruction of its habitat. While the hummingbird is not endangered in the United States, Ross Hawkins worries about developments in Ecuador.

"There are places in the tropics that haven't been disturbed for tens of thousands of years," he says. "And now, in the case of Ecuador, they're putting in an oil pipeline right through the middle of the first declared important bird [sanctuary] area in South America that has many critically endangered species, not just hummingbirds, but other birds there. If you don't have but a hundred birds left of a particular species and you start putting a pipeline through its prime breeding territory, what are the implications of that?"

The pipeline is expected to bring millions of dollars in oil revenues, but protests over its possible environmental impact have delayed its construction. Meanwhile, the United States is now working with Mexico to improve river and land quality for thousands of migrating hummingbirds.