Isla San Esteban & Isla Rasa, Baja California, Mexico
Endemism is that result of evolution that stems, at least in part, from gene mutation and genetic isolation. Like the Galápagos Islands and other special places on Earth, the islands of Mexico’s Gulf of California harbor endemic species of plants and animals…species that are found nowhere else. We had a chance to look for some of those species today, and to think about the factors that govern isolation. Isla San Esteban is but one example of a desert island that supports unique forms.
We walked slowly this morning, eyes high and eyes low, searching for two fascinating reptiles. The pinto chuckwalla, an herbivorous lizard, is the largest of all chuckwallas and is endemic to this island. Hunted heavily by the early people of the gulf, it has persisted, and may even be more abundant now than at anytime in the past few decades. Most of our walking groups were able to smile at this sad-faced, pudgy animal as it rested quietly on a shaded branch or gathered heat from the morning sun. That heat is essential. Movement among poikilothermic animals - those whose body temperature is the same as the air temperature around them – depends on the sun’s energy. If they can warm up, they can move, and the warmer they are the faster they move. Our attempts to pick up a chuckwalla proved the point; it was warm very early today, and the chuckwallas were not about to be caught.
An endemic subspecies here is the spiny-tailed iguana. We looked up to find these characters, high on the tall cardon cacti, licking their red lips – lips that were coloured by the ripe fruit of the cordons. And among the many plants here was an endemic cactus of the genus Mammalaria – a “nipple” cactus.
After a presentation on seabird ecology and a light lunch, we visited another island, one that supports two near-endemic birds. Isla Rasa, a small, flat islet, is a spectacular seabird nesting site. As many as 500,000 birds may be here at the peak of hatching. We were able to get ashore for first-hand looks at about 95% of the world’s Heermann’s gulls and 98% of the world’s elegant terns. What a sight! Although these two species cannot be considered endemic to Rasa, only handfuls nest elsewhere. Now protected, Isla Rasa is a prime example of the colonial nesting habits of most seabirds. Researchers on the island came aboard the Sea Voyager to describe their work, and in particular their attempts to document the fish species, and even the ages of the fish, that are being fed to the chicks. Is commercial fishing endangering the stocks? Is global warming affecting the foraging habits and survival of the terns and gulls? Can we expect this important island to continue to produce these birds if atmospheric conditions change as is predicted by many scientists? An extensive and continuous data base is necessary if we are to answer such questions, and this data base is still being added to after 30 years of study here. We can look forward to hearing some firm answers.
Endemism is that result of evolution that stems, at least in part, from gene mutation and genetic isolation. Like the Galápagos Islands and other special places on Earth, the islands of Mexico’s Gulf of California harbor endemic species of plants and animals…species that are found nowhere else. We had a chance to look for some of those species today, and to think about the factors that govern isolation. Isla San Esteban is but one example of a desert island that supports unique forms.
We walked slowly this morning, eyes high and eyes low, searching for two fascinating reptiles. The pinto chuckwalla, an herbivorous lizard, is the largest of all chuckwallas and is endemic to this island. Hunted heavily by the early people of the gulf, it has persisted, and may even be more abundant now than at anytime in the past few decades. Most of our walking groups were able to smile at this sad-faced, pudgy animal as it rested quietly on a shaded branch or gathered heat from the morning sun. That heat is essential. Movement among poikilothermic animals - those whose body temperature is the same as the air temperature around them – depends on the sun’s energy. If they can warm up, they can move, and the warmer they are the faster they move. Our attempts to pick up a chuckwalla proved the point; it was warm very early today, and the chuckwallas were not about to be caught.
An endemic subspecies here is the spiny-tailed iguana. We looked up to find these characters, high on the tall cardon cacti, licking their red lips – lips that were coloured by the ripe fruit of the cordons. And among the many plants here was an endemic cactus of the genus Mammalaria – a “nipple” cactus.
After a presentation on seabird ecology and a light lunch, we visited another island, one that supports two near-endemic birds. Isla Rasa, a small, flat islet, is a spectacular seabird nesting site. As many as 500,000 birds may be here at the peak of hatching. We were able to get ashore for first-hand looks at about 95% of the world’s Heermann’s gulls and 98% of the world’s elegant terns. What a sight! Although these two species cannot be considered endemic to Rasa, only handfuls nest elsewhere. Now protected, Isla Rasa is a prime example of the colonial nesting habits of most seabirds. Researchers on the island came aboard the Sea Voyager to describe their work, and in particular their attempts to document the fish species, and even the ages of the fish, that are being fed to the chicks. Is commercial fishing endangering the stocks? Is global warming affecting the foraging habits and survival of the terns and gulls? Can we expect this important island to continue to produce these birds if atmospheric conditions change as is predicted by many scientists? An extensive and continuous data base is necessary if we are to answer such questions, and this data base is still being added to after 30 years of study here. We can look forward to hearing some firm answers.
