â€œâ€¦ 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 strangerâ€™s craft or power.â€
We had just seen a GalÃ¡pagos 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 worldâ€™s largest active calderas, Cerro Negro, on Isla Isabela. We walked carefully along the border of the volcanoâ€™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 GalÃ¡pagos 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 GalÃ¡pagos are a disaster. Darwin recognized this danger almost two centuries ago.
GalÃ¡pagos 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 hawksÂ had no natural enemies but now their eggs, nestlings and fledglings are easy prey for cats.
A census of GalÃ¡pagos 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 GalÃ¡pagos. 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 GalÃ¡pagos; 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 â€œimproveâ€ 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 climateâ€™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 â€œgo to heavenâ€. 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 GalÃ¡pagos. 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 natureâ€™s many wonders.
Â© Richard Grossman MD, 2013