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Hatchling Volcano
The tropical sun is shining without mercy over Tortuguero beach and village.
The nesting turtles are slowly becoming fewer, but with the many turtles this
year there is still a substantial number of them crawling up the beach at
night to deposit their eggs. During this time of year, the small hatchlings are
also beginning to appear in multitude.
An average green turtle nest contains approximately 107 eggs. There is much
variation in the nest size and we have encountered nest as small as 70 eggs
and as large as 160 eggs this season. Not all of the turtle nests will hatch and produce hatchlings. Some nests will satisfy the taste of coatimundis, dogs or human poachers. Also, in almost each nest there are some eggs that do not hatch for some reason. So far this year, we have excavated over 35 green turtle nests after the hatchlings have emerged. On average, 85% of the eggs hatched successfully and the rest remained unhatched. Some eggs had been depredated by crabs,
ants or maggots. Others had stopped developing at different stages of
development, some just before the hatchlings were about to hatch. We have
recorded two albino hatchlings, one albino hatchling with a deformed head,
and a set of triplets in the same egg.
When the hatchlings have broken the eggshell with their eggtooth, they start
moving up toward the surface. The movement of one hatchling triggers
the rest of the hatchlings into motion. The hatchlings move their little
flippers to push sand down below them and slowly they ascend together to the top of the nest. If they reach the surface during the day, the high temperature will make them
immobile. They will wait just below the surface until the sand becomes cooler,
which it does after dark. When the temperature is right, the hatchlings
start emerging en masse. They emerge at night to avoid being cooked on the
hot sand during the day and to avoid predators that are active during the day. The
dark coloration of the carapace of a green turtle hatchling provides a good
camouflage against the dark sand background. Also, by the time they reach
the sea there may be fewer predators active in the coastal waters at night.
By the time the sun rises the little hatchlings will be far away from the
coast in deep waters where potential predators may be less common.
A couple of days ago I was walking the entire beach to determine if there
had been any sea turtle poaching the previous night. I had walked for about
nine miles and it was almost eight o'clock in the morning. It was slightly
overcast and the beach was still not too hot for hatchlings. As I
was walking along in the surf zone, I saw a group of black vultures moving
around further up the beach. Vultures are opportunistic feeders that will
take carrion or other food items they find. The black vultures are plentiful during the turtle nesting and hatchling season, no doubt in search of turtle eggs and hatchlings.
I walked up toward the vegetation line to find out what the vultures found so interesting. Most of the vultures immediately took off in flight, some after an initial run of a couple of
feet. They looked like dinosaurs when they ran along the beach, with their
beady eyes trying to discern if the person walking up the beach had
hostility in mind. Only one vulture stayed for longer than the rest but as I
got closer the instinct of flight became stronger than the focus of feeding.
It left behind an injured hatchling laying in the sand.
The vultures had found a nest with hatchlings that had reached the surface
of the sand and become immobile in the morning sun. The top
hatchlings were almost out of the nest, and those were the ones
that the vultures had found. The injured hatchling on the beach was still
alive and started to crawl towards the sea. It looked like its front flippers had be broken and it had to use its rear flippers to
move along the sand surface.
As I was contemplating the destiny of the little chelonid, I turned around
to look at the rest of the hatchlings. The vultures must have been picking
around the nest and triggered the remainder of the hatchlings. They were all
trying to get out of the nest and make it down the beach. They were crawling
on top of each other in a competition to reach the sea. The nest looked like a volcano with lava hatchlings flowing out of the active crater. The eruption lasted for only a couple of minutes before the little turtles were all scrambling toward the cooling waves.
Adult green turtles drag themselves up the beach with simultaneous movements
of their front flippers. Green turtle hatchlings, however, weigh only forty
grams or so and can move rapidly down the beach with alternating movements
of one front flipper and the opposite rear flipper, followed by the other
pair of front flipper-opposite rear flipper. In spite of their minuscule
size, they move rapidly down the beach toward the sea which is their true
habitat.
Minutes after the vultures had flown away, the only evidence remaining of
the amazing act of hatchling emergence was a hundred little tracks extending
from the nest near the vegetation line down to the edge of the sea. The waves
were washing away the last of the black and white hatchlings. Maybe one of
them will be lucky enough to survive the perils of life in the ocean and
return to the black sand beach of Tortuguero in 25-50 years time, ensuring
the continued survival of their ancient kind.
Pura vida,
Sebastian Troëng
Research Coordinator
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