Category: conservation biology

Galápagos Hawk

 

“… the introduction of any new beast of prey must cause [extinction] in a country, before the instincts of the indigenous inhabitants have become adopted to the stranger’s craft or power.”

Charles Darwin

 

We had just seen a Galápagos hawk soaring overhead when we heard an incongruous sound; here were cats mewing beside the path. I caught a glimpse of a tabby kitten with the bluest eyes.

“I like cats” the guide said “but I’ll have to report these to the rangers. They will come here with dogs.”

We were returning from hiking on the tortured volcanic surface of one of the world’s largest active calderas, Cerro Negro, on Isla Isabela. We walked carefully along the border of the volcano’s crater; the path was narrow and muddy with a fatal drop-off. Fortunately there was a slender border of green between the sheer wall and us. This is where these feline invaders lived.

Cats are an exotic species in the Galápagos Islands, maybe introduced to catch the rats that were also introduced accidentally by man. Sometimes biocontrol (using one species to control another) works out well, but other times it is a disaster. Cats in the Galápagos are a disaster. Darwin recognized this danger almost two centuries ago.

Galápagos hawks only live on that isolated group of islands; they are endemic, meaning they are found nowhere else in the world. They nest in low trees and in the hollows of walls of the volcanic rock of which the islands are made. Formerly the hawks had no natural enemies but now their eggs, nestlings and fledglings are easy prey for cats.

A census of Galápagos hawks taken late in the 20th century estimated fewer than 1000 individuals. These magnificent birds have been eradicated from much of their former habitat so now this species is found on only four of the islands. The Red List of Threatened Species states that these hawks are vulnerable to extinction because of introduced predators and their small population.

Of the six ways that mankind sends other species to extinction, perhaps introduction of exotic plants and animals is the second most common.

Exotics may not seem so bad since our homes and gardens are filled with beautiful plants from other lands. Unfortunately they can cause problems in at least three ways. Exotics may outcompete natives. They often don’t have local pests to help control them, as is the case with cats in the Galápagos. Pollinators often find exotic plants unattractive so pollinators become scarce, but they are essential to native species.

Ecuadorians are doing a fine job of dealing with exotic species. We paid $100 for a permit to visit the Galápagos; that money helps fund the rangers and other efforts to protect the unique environment. Our small group of “adventure tourists” also was given an orientation urging us to respect this amazing place with its many endemic plants and animals.

Destruction of habitat and climate change are two other ways that humans are causing the mass extinction of species. As the numbers of humans has grown, and as we “improve” the landscape with more agriculture and construction, there is simply less space for other species. Not only do we use more and more of the land, but also we break up what there is so it is of less value to critters.

Climate change is also wreaking havoc with many plants and animals. Species that need cold, or whose pests are controlled by cold, are susceptible to our climate’s warming. A local example is the little pikas that live high in the mountains. They are happiest with cold winters and lots of snow. They can move up in altitude as the world warms, but our mountains only go so high. If the world gets too hot they will all “go to heaven”. Another example is the spruce bark beetle, which has killed so many of our spruce trees. Sub-zero temperatures and adequate moisture have controlled this pest in the past, but the beetles are thriving with climate change and drought.

There is hope for endangered species, at least in the Galápagos. Efforts to protect their endemic hawk have apparently been successful because I have heard that there are now almost 2000 members. There are even plans to reintroduce them to islands where they had been driven to extinction. I feel good that our small contributions paid for by the permits to enter the islands have been effective in helping to preserve one of nature’s many wonders.

© Richard Grossman MD, 2013

“Whatever happens to this single animal, let him always remind us that the fate of all living things on Earth is in human hands.”

Wording on information panel beside Lonesome George’s pen

            The last member of a species died this year. “Lonesome George” was the only Pinta tortoise left in the world.

Pinta is one of the Galapagos Islands. These islands are remote from the mainland of South America, and far enough from one another so animals cannot interbreed. Separation over eons of time caused the development of distinct species on each of the islands. Perhaps the best known are finches.

HMS Beagle, on which Charles Darwin was the naturalist, made a stop on the Galapagos in 1835. A careful observer, Darwin found that there were a variety of finches on the Galapagos archipelago. Each species had its own shaped beak, and the beaks were gradated from small to large. Beak size and shape varied by diet, which in turn was determined by the niche that the bird occupied. This range in size was a clue that lead Darwin to understand evolution.

The volcanic Galapagos are about 600 miles from the mainland of Ecuador and separated by up to 50 miles of open ocean from each other. If the islands were closer together, the birds could have easily flown from one to the other and interbred, and they probably would not have developed different niches and beaks. It is only a rare storm that carries the birds from one island to the next.

The Galapagos tortoises offer another example of speciation. They are huge, the largest weighing over 800 pounds and having shells 6 feet long. They eat plants, including cacti—up to 80 pounds a day!—and can live over 100 years. They have an interesting mutualism with some finches. The birds hop on the ground facing the tortoise, at which point the giant extends its neck and rises up on its legs. The birds will then groom the reptile.

These giant tortoises are not very good swimmers, which has contributed to developing at least ten different varieties with significant differences. Whether the variations are great enough to be considered different species or just subspecies (races) is not clear.

Galapagos males assert dominance over one another by seeing who can reach his head highest. A peaked shell differentiated the Pinta Island tortoise, allowing their necks to reach higher than other varieties.

`           The meat of these animals is reportedly tasty. Sailors collected them by the thousands in the 19^th Century, then turned them upside down and kept them as living larders on board ship. The tortoises could last for more than a year without food or water. This careless harvesting probably killed off some varieties and has caused confusion for biologists who are trying to figure out what species lived where.

Goats were introduced to Pinta Island in 1958. They created havoc by eating much of the food that tortoises like, further jeopardizing the reptiles. It took years to eradicate these hungry mammals.

The last known Pinta Island tortoise was found in 1971 and taken to the Charles Darwin Research Station on the Islands, where he attracted tens of thousands of visitors. Nicknamed “Lonesome George”, he was already mature so there is no way of telling how old he was.

Several expeditions combed Pinta for other members of the species. They found several skeletons but no live animal, and no sign of an animal that might have been recently alive. Lonesome George was unique.

In an effort to preserve at least part of his genetic pedigree, females of other tortoise subspecies were introduced. Unfortunately, Lonesome George never took much of a liking to them and there were no offspring. There had been thoughts of trying to preserve his lineage in other ways such as in vitro fertilization, but that wasn’t practical.

Lonesome George was found dead on June 24^th. His was the 802^nd known species (or subspecies) to be driven extinct in the past 500 years; almost all these extinctions have had a human cause. The government of Ecuador had made every effort to protect George’s life and preserve the Pinta species. This effort was appropriate for the first country in the world to recognize the rights of nature.

George was lucky in that he belonged to a species that was recognized as being at risk of extinction. Biologists suspect that thousands of species go extinct every year without ever being described, named or their loss even noticed.

© Richard Grossman MD, 2012