The Galapagos Islands, smack-dab on the Equator, 600 miles out into the Pacific from South America, are the tips of huge undersea volcanoes, some extinct, some still active. Covered with black lava and other volcanic deposits, they present a bleak and foreboding aspect to visitors stepping ashore, including their most famous visitor – Charles Darwin, who spent 35 days there in 1835. The unusual animals and plants of these islands played an important role in Darwin’s thinking and the development of his theory of evolution by natural selection.

The Darwin connection and the unique life of the Galapagos make the islands a dream destination for biologists like Ron and Lee Davis of Orono. After decades of dreaming, this year they finally spent time there, visiting the islands from Jan. 27 to Feb. 3. Ron Davis will describe their experiences with an illustrated talk at 7:30 p.m. Wednesday, Sept. 27, at Fields Pond Audubon Center in Holden. Through his photographs, Bangor-area residents will see remarkable creatures that exist only in the Galapagos.

Most famous is the giant Galapagos tortoise, which weighs up to 550 pounds and lives more than 100 years. In addition, large golden-colored iguanas roam the woodlands, munching on their favorite food, spiny cactus pads. Red-footed and blue-footed boobies with equally colorful beaks and a clownlike appearance establish breeding colonies on the islands. Of interest to Mainers is a version of the cormorant that is flightless, although it still stands on shore with its tiny wings extended, Davis said.

Because there are few predators on the islands, the animals are famously tame, which can make photographing them a joy, and Davis said he spent most of his time behind the lens of his camera. More than 90 percent of the area of these Ecuadorian islands is a national park, affording strict protection for the many animals and plants that are especially vulnerable to human impacts.

When the volcanoes that make up the Galapagos emerged from the ocean – some of them a few million years ago and others only thousands of years ago – they were barren of life. Now, low coastal areas of the islands are covered by desertlike vegetation, including tree-size cacti, while the slopes of the Katahdin-high volcanoes, which receive more rain and are often enveloped by clouds, support luxuriant forests.

How organisms colonized these remote oceanic islands has intrigued biologists. Winds blow microorganisms, fungal spores, spiders and insects hundreds of miles, and seeds are carried by birds. Natural rafts of debris are brought to the sea by rivers and then moved great distances by ocean currents. Such rafts from South America are probably the major source of animals and plants of the Galapagos, Davis said. Most animals and plants of these islands bear an affinity to animals and plants of South America, but with differences. As Darwin noticed, they changed from their closest South American relatives, and even from island to island, as an adaptation to their new environments.

The marine iguana of the Galapagos, the only marine lizard in the world, has evolved the ability to excrete (through its nostrils) the salt from the marine algae it eats, Davis said. Many of the Galapagos bird species are dark gray, blending into the volcanic background. As a laboratory of natural selection, the Galapagos have become a Mecca for naturalists and for tourists who delight in close views of unusual animals and plants.

The Davises chose a trip with well-trained natural history guides. They were in nearby Peru before the Galapagos trip, doing volunteer research sponsored by Earthwatch Institute on macaws of the Peruvian Amazon. They flew from Lima, Peru, to Quito, Ecuador, to the Galapagos, where they traveled from island to island on an Ecuadorian ship. At night, while they slept, the ship took them from one island to another. Zodiacs ferried them ashore to a different island or two each day. Various nationalities were represented in the 75 or so ecotourists on the ship, and the guides were multilingual.

The temperature was in the 80s during the daytime, moderated by the surrounding ocean. The days were sunny, and the sea was calm. Storms are rare in the Galapagos, according to Davis. He was struck by the magnificent golden beaches and the bright red crabs that glared from the black lava shores.

The Davises were able to get close enough to sea lions to see babies nursing, although they kept a safe distance from large males. They saw prickly pear cactus that had evolved into 30-foot-tall trees (only to be found on the Galapagos). They were delighted by the black and white Galapagos penguin, a diminutive 14 inches tall. And everywhere there were reptiles, from small lava lizards 4 to 10 inches long, to lumbering iguanas and giant tortoises.

They found on the Galapagos a kind of paradise, but a paradise marked by the constant struggle for survival.

“It was the trip of a lifetime,” Lee Davis said. “It met all our expectations.”

For information on the Galapagos Islands presentation Sept. 27, call 989-2591.