Isla Rasa, Baja California Sur
Yelp! Yelp! Yelp!
Colonial-nesting seabirds. What a sight! What a sound! What a marvelous adaptation to ensure survival of the species!
Isla Rasa, a small, flat island in the midriff section of the Gulf of California, is a classic example of a seabird colony. Almost half a million birds strong, it is dominated by 95% of the world’s population of Heermann’s gulls and perhaps 98% of the world’s elegant terns. And elegant they are. Their shiny white bodies are highlighted by a long, pumpkin-orange bill and a coal-black, shaggy crest. Thousands were around us today. They had just arrived at this, their natal island, and were courting, displaying, arguing over mates and flying over us like darts. Their raucous kreeik calls rang across the guano-covered rocks.
Many more will come, joining the early arrivals and quickly hyper-compacting into a tight mass, with densities as high as 19 nests per square meter. Protection! That is what they seek. Facing such a dense crowd, an invading predator such as the yellow-footed gull (itself an endemic nester in this bountiful gulf) will have to avoid an angry “cactus” of stabbing bills in order to steal an egg or downy chick.
As with all colonial-nesting birds, some losses can be tolerated. The peregrine falcons and common ravens here will take a tiny percentage of the population. With such huge numbers and incredible densities, an annual cohort of young will hatch, fledge and fly off, eventually to return, sexually charged and ready to carry on the reproductive prerogative.
The Heermann’s gulls were here as well. Most had already established their pairs, had laid their first egg or two, but were still copulating repeatedly. They present another barrier to yellow-footed gull predation, intercepting the interlopers and standing their ground. The terns take advantage of the surrounding wall that they put up.
We were guided to and on this tiny island by Enriqueta Vilarde, now in her 28th year of directing research and conservation projects on Rasa. It is hard to imagine any scientist having had a longer continuous devotion to such a small, but important part of the natural environment. As a result, Isla Rasa will continue to produce beautiful seabirds.
But how many such islets have already been lost throughout the world? Man’s developments, over-exploitations, and introduction of devastating terrestrial predators have left many nesting areas devoid of birds. Only persistent protection can prevent future losses. Enriqueta and her assistants deserve our thanks. We want others to hear the pleading Yelp of the Heermann’s gull.
Yelp! Yelp! Yelp!
Colonial-nesting seabirds. What a sight! What a sound! What a marvelous adaptation to ensure survival of the species!
Isla Rasa, a small, flat island in the midriff section of the Gulf of California, is a classic example of a seabird colony. Almost half a million birds strong, it is dominated by 95% of the world’s population of Heermann’s gulls and perhaps 98% of the world’s elegant terns. And elegant they are. Their shiny white bodies are highlighted by a long, pumpkin-orange bill and a coal-black, shaggy crest. Thousands were around us today. They had just arrived at this, their natal island, and were courting, displaying, arguing over mates and flying over us like darts. Their raucous kreeik calls rang across the guano-covered rocks.
Many more will come, joining the early arrivals and quickly hyper-compacting into a tight mass, with densities as high as 19 nests per square meter. Protection! That is what they seek. Facing such a dense crowd, an invading predator such as the yellow-footed gull (itself an endemic nester in this bountiful gulf) will have to avoid an angry “cactus” of stabbing bills in order to steal an egg or downy chick.
As with all colonial-nesting birds, some losses can be tolerated. The peregrine falcons and common ravens here will take a tiny percentage of the population. With such huge numbers and incredible densities, an annual cohort of young will hatch, fledge and fly off, eventually to return, sexually charged and ready to carry on the reproductive prerogative.
The Heermann’s gulls were here as well. Most had already established their pairs, had laid their first egg or two, but were still copulating repeatedly. They present another barrier to yellow-footed gull predation, intercepting the interlopers and standing their ground. The terns take advantage of the surrounding wall that they put up.
We were guided to and on this tiny island by Enriqueta Vilarde, now in her 28th year of directing research and conservation projects on Rasa. It is hard to imagine any scientist having had a longer continuous devotion to such a small, but important part of the natural environment. As a result, Isla Rasa will continue to produce beautiful seabirds.
But how many such islets have already been lost throughout the world? Man’s developments, over-exploitations, and introduction of devastating terrestrial predators have left many nesting areas devoid of birds. Only persistent protection can prevent future losses. Enriqueta and her assistants deserve our thanks. We want others to hear the pleading Yelp of the Heermann’s gull.
