This post is also available in: Dutch.
We have given ample attention to the miserable situation the inhabitants of Curaçao found themselves in ever so often in historical times, due to the lack of fresh water, and the ingenious solutions necessary to survive. When the circumstances got too extreme, humans, at least the white part of the population, had the choice to leave the Island, to leave on a ship and return to the motherland. Such a choice the slaves did not have, however. Nor the animals on the island. It is not an option for a parakeet to fly to Venezuela in the dry season, the period of little food. If they would attempt such a passage anyway, probably half of their number would perish at sea because of pure fatigue. The lack of migration capability of our parakeet and many other bird species on the Island, is the result of an evolutionary process that took thousands of years. Some types of birds in the world chose to search for better places to travel to in order to seasonally avoid difficult times. They evolved into migratory species. Other birds chose to adapt to the circumstances and to make do with less food and harsher climatological conditions. A very different strategy, which often resulted in the animals turning into opportunists.
Opportunism is a valuable property on an island where normally only a few months of the year are hospitable enough to live generously. The rainy season! In several species on the island you’ll clearly observe typically opportunistic behavior. The trupial, generally known as a fruit eater, will then snack all too well on insects as well as unripe cactus fruits. When it gets the chance it will even devour an egg or a small bird for the necessary proteins.
Opportunistic behavior is not only clearly visible in the menu of the animals and the hunting behavior to find food. Within reproduction is it even more clearly visible, to an extent that might even be repugnant to humans.
Green energy slurpers
An example is the popular and beloved Blue-tailed Emerald Hummingbird (Chlorostilbon mellisugus). This green flashing emerald, that we lovingly admire when it visits our flowers, only builds nests in the rainy season, when it is guaranteed that there are enough flowers to collect nectar from to feed the hatchlings. To the expense of lots of energy, a small nest is constructed from bits of bark, grass and leaves which are glued together with cobwebs. The inside of the nest, which is shaped like half an eggshell the size of a marble is covered with lint, consisting of fine bits of grass, cobwebs, bits of our mop left outside, and feathers. Within this soft masterpiece two eggs are laid, each in size about one third of the total length and weight of the mother. The father plays no role in raising his offspring, and only takes care of the defense of his territory in which the female’s nest is located. The hatchlings are fed with flower nectar and small insects. During the lush rainy seasons we experienced in recent years, the female will be able to find sufficient food for both youngsters to grow into young adult hummingbirds.
But it also happens that the rainy season ends as abruptly as it started and that the once-lush flowering plants stop the production of nectar early in the season. During such a period, youngsters will receive less and less food from their mother. If such a period turns into a real dry period, then the young that first crawled out of the egg, which is in general stronger than the second, will throw its weaker brother or sister from the nest. It seems an act of senseless violence, but it is a necessity in nature. If this is not done then both young will get too little food, hence both will die prematurely. This would be quite a tragedy for the mother, since neither of its offspring will then continue the genetic line. If only one remains, the strongest, then at least one young has the chance to continue the bloodline.
The Curaçao deer is also opportunistic in reproduction. The climate on the island and the resulting fluctuations in food supply create a biological regulation that is still little understood. In years that survival is problematic, even in the rainy season because of a lack of rain (the last time in 2009), the deer will usually not reproduce, or will at most get one young. During such years almost no ‘bambi’s’ are spotted after the period of gestation. In a normal rain year, the production of a single bambi per female is common. In a year with extreme rainfall, as in 2006 and 2010, a significant number of females will give birth to twins. It’s almost kind of a built in on/off switch that very effectively adapts the number of offspring each year to the presence and levels of food, in order to optimize the chances of survival.