Fauna of the Galápagos Islands
The fauna of the Galápagos Islands represents a unique ecosystem characterized by a high degree of endemism due to the islands' isolation from the nearest landmasses. This biodiversity primarily includes reptiles and birds, with around nineteen out of twenty-seven reptile species being endemic, such as geckos, iguanas, and the renowned Galápagos tortoise. The islands' avian population features six endemic seabird species and twenty-two endemic landbird species, including the famous Darwin's finches, which have adapted to various ecological niches. Notably, the Galápagos penguin is the northernmost and one of the smallest penguin species, while the flightless cormorant has adapted to its environment by losing the ability to fly.
Mammals are less diverse, with only eight endemic species, primarily consisting of rice rats and bats, alongside non-native mammals that threaten native populations. The insect population is moderately extensive, mostly consisting of nocturnal species, with endemic scorpions and a variety of spiders. The delicate balance of this ecosystem is increasingly challenged by climate change, particularly through phenomena like El Niño and La Niña, which affect weather patterns and, consequently, species survival. Overall, the Galápagos Islands showcase a fascinating yet vulnerable tapestry of life shaped by their unique geographic and environmental conditions.
Subject Terms
Fauna of the Galápagos Islands
The Galápagos are oceanic islands created by submarine volcanoes that emerged from the ocean devoid of life. Because of the great distance between an oceanic island and the nearest continent, only animals and plants that can disperse easily through the air or water are likely to reach such an island. Even fewer will survive its particular environmental conditions and thrive. For this reason, oceanic islands tend to be disharmonic.
Furthermore, increased frequency of the storm systems El Niño-Southern Oscillation (ENSO) and La Niña, caused by climate change, has increased general weather variability and has posed a threat to the biodiversity of the Galápagos. Changing water temperatures, algae biomass, and the variation of an abundance of rainfall due to ENSO events or a lack of rainfall due to La Niña events has changed the way species inhabit the islands as well as population numbers.
For animals to reach the Galápagos before humans arrived, there were only three options: by sea, whether by swimming, floating, or drifting on natural rafts of logs or other vegetation; by air, either by flying or drifting in wind currents; or by hitching a ride on or in the body of another animal. As a result of such limited, haphazard possibilities, freshwater fishes and amphibians are totally absent from the islands, and endemic mammals are few. Only birds and reptiles represent vertebrates, and only beetles and butterflies represent invertebrates.
Reptiles
Reptiles dominate the Galápagos. Though sources vary on exact numbers, around nineteen out of twenty-seven species are endemic. They include geckos, snakes, lava lizards, iguanas, and giant tortoises. Geckos are small, mostly nocturnal lizards. The one endemic snake is a small constrictor. Lava lizards are so named for their habit of basking on lava rocks and range in size up to twenty-five centimeters (almost ten inches).
The islands have both land and marine species of iguanas. Land iguanas grow up to 1.2 meters (almost four feet) long, have a large dorsal crest, and can live up to seventy years. They prefer fruits, flowers, cactus pads, and other vegetarian fare but also consume insects and carrion. The marine iguana is the only sea-going iguana in the world and can drink seawater, utilizing special salt glands to excrete the excess salt. It spends most of the day basking but dives to depths of twenty meters (over sixty feet) to feed almost exclusively on marine algae. It can reach a length of 1.5 meters (five feet) and live up to thirty years.
The most famous reptile on the islands is the Galápagos tortoise, Geochelone elephantopus. Males can weigh up to 250 kilograms (550 pounds); females are considerably smaller. They drink from pools at any opportunity and browse on plants, but they can survive a year or more without eating or drinking and can live 170 years or more. There are two distinct types of tortoises, with one intermediate type. One type has a dome-shaped carapace and lives in moist, lush areas where vegetation is abundant and easy to reach. The other inhabits more arid regions and has a saddle-shaped carapace, allowing extension of its long neck to reach leaves and cactus pads high overhead. It is this tortoise’s distinctive shell that gave the islands their name—Galápago refers to a light saddle or sidesaddle in Spanish.
Birds
Although seabirds are abundant on the islands, most are non-native migrants. Only six seabird species are endemic—the lava and swallow-tailed gulls, the waved albatross, the flightless cormorant, the Galápagos Petrel, and the Galápagos penguin. The Galápagos penguin is the northernmost penguin species and one of the smallest, standing forty centimeters (sixteen inches) tall. The flightless cormorant has a strong, hooked beak and vestigial wings. Like the penguin, it swims underwater to catch fish, propelled by its webbed feet.
Twenty-two out of twenty-nine landbirds are endemic. There are four species of mockingbird, one dove, one flycatcher, one hawk, one martin, one rail, and thirteen species of Darwin’s finches. Darwin’s finches all originated from a species native to the Caribbean, Melanospiza richardsonii, evolving over time into thirteen species with different bill sizes and shapes and varying habits.
Mammals
Not including the sea lions that gather in colonies on the beaches, only eight species of mammals are endemic to the Galápagos, six species of omnivorous rice rats and two species of bats. Unfortunately, many non-native mammals, feral and domestic, have moved in and decimated many native populations of both flora and fauna. Lush vegetation has been converted to grazing land for goats, cattle, and horses. Donkeys trample tortoise nests while pigs root up and devour the eggs of giant tortoises, sea turtles, and birds. Dogs, cats, and non-native rats prey on any reptile or bird they can catch.
Arthropods
About one thousand insect species inhabit the Galápagos. Because of the arid environment, most are nocturnal. Although there are relatively few species, insects are plentiful, particularly during the rainy season.
Of the arachnids, two endemic species of scorpions are found on the islands. Although there are over fifty spider species, only a few are endemic. The least popular animal on the island is an endemic centipede that can grow as long as thirty centimeters (approximately one foot) and administers a very painful bite.
Principal Terms
Carapace: Hard case covering the back of an animal
Disharmonic: Ecologically unbalanced
Endemic: Belonging to or native to a particular place
Nocturnal: Active at night and dormant or asleep during the day
Vestigial: Less developed or degenerated from an original, useful form
Bibliography
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