Editor's Note: Dr. Sara Bennett is a biologist who leads a small NGO, Maikuchiga, in Colombia’s Amacayacu National Park that operates a rescue center for orphaned animals. The Park, in the nation’s Amazonas state, is traversed by the Amazon River. This post is one in a series from Dr. Bennett. Post originally developed May 5, 2010.
After the epic battle with the bees, the toucans seem not to be nesting this year.
It’s always trickier perceptually to notice an absence than a presence, something NOT happening that’s part of one’s peripheral normalness. I finally twigged on this, and after registering my own observation and confirming it with the guys, then noticing that I’m disappointed, began to wonder in background mode, How come?
On the front porch, holding Rosie, the long-tailed, adolescent spider monkey (who is really a little too big for this but didn’t have enough hugs earlier in her life so we’re doing some catch-up), a nice soft, wiggly solidness centering the universe for a moment in my arms, I was aware as well of all the colors of the early morning forest around us.
It’s usually hard to see the trees because of the forest here, but lots of species have new leaves right now and for a few days each one is distinct in hue and overall effect (it’s lovely, thank you world, nicely done). Then I suddenly get what’s going on with the toucans. This year it’s about new leaves, not fruit.
I seem to be mostly cheerfully oblivious of a lot of stuff until I experience something entirely different and start noticing what I’d taken for granted and asking, so what’s going on? The seasons, for instance. You don’t have to pay much attention to notice the seasons changing in New England (just go to the drugstore). Even outside, the changes are pretty obvious even for someone like me. Oh, it’s cold. Oh, it’s hot. Oh, it’s snowing. Oh, there are all these nice leaves to shuffle through. Oh, the robins are back.
In equatorial regions, we get seasons, too. But it’s not about temperature, at least not to the same degree. It’s about rainfall. We’re not in the rainiest part of the Amazon, but even here people joke, “In summer, it rains every day; in winter, it rains all day”. And the river goes up and down – a lot: the difference between high-water and low-water averages 13 meters, and we’re hundreds of kilometers from the Atlantic.
It’s pretty easy to notice the difference when you live in the floodplain. Last year, for instance, the water came right up to the floor (the house is built on three-meter stilts); when a pequepeque (the people’s long-tailed motorboat) went by in the creek, the wake came sloshing up through the cracks in the floor. Each time this happened, the dog stood on guard and barked to make it go away.
The difference makes a huge difference to all players in the game - plants, animals, and people. As little as a centimeter higher or lower in water level in the river translates horizontally to who knows how many (LOTS OF) square kilometers of forest that is—or isn’t—flooded. And that translates to all those fishes who do – or do not – have access to all those fruits that fall and therefore will—or will not—make lots of baby fish to make their way up the food chain. And, for the plants, if it’s a good thing or not for your fruits to be eaten (and the seeds digested or dispersed) by fishes or not. Normally there is a huge peak of fruit as the water rises and the flooded forest is the place to be. Sometimes where a monkey troop is going at it in a fruit crop, there’ll be all sorts of other critters attracted to the activity— frugivorous birds taking advantage of all those keen monkey eyes watching out for and warning about predators; insectivorous birds ditto for the vigilant eyes plus all the big insects fleeing monkeys; fish taking advantage of all the fruits, insects, and other canopy flotsam and jetsam (monkeys tend to be messy eaters); herons, kingfishers, piscivorous fish, dolphins, and human fishermen piling on to the general feeding frenzy.
My interpretation of all the new leaves right now is that the trees didn’t get the appropriate cue from the physical world (more likely a set of cues) to flower this time around, and the pulse of nutrients in the water, when it finally came, has been invested in growth and maintenance instead (new leaves, that is). Likewise, the toucans, which are frugivores and reproduce when there is an abundance of fruit crops. I wouldn’t be surprised if the toucans are growing new feathers right now in a Plan B of their own.
There is hardly any long-term empirical information about phenological (seasonal) patterns in tropical rainforests. My own operative hypothesis is that there are complex combinations of temperature and moisture cues that trigger different enzyme pathways in the bud meristems for leaf abscission, leaf growth, or flower development. Each species’ unique and fine-tuned response to these physical variables results in the temporal synchronization of the population. The overall ecosystem phenology is a higher-order consequence of individual species physiologies. Moreover, my impression is that the physical world is running the show, in which the plants respond to the weather cues and the animals respond to plant cues. (As in, I’m speculating that the toucans aren’t nesting this year because there’s less than critical mass of fruit available.)
The Amazon is often referred to (mostly by the regional tourist industry) as the “pulmón del mundo” (the world’s lungs). I prefer “the world’s heart” as a metaphor, because the Amazon forest acts as a heat pump that transfers heat from the equator to higher latitudes as part of the overall powering mechanism of global air and water currents. And, as the saying goes, “What goes ‘round, comes ‘round.” The Amazon’s climate is, in turn, determined primarily by these global air and water currents. Secondarily there is an internal feedback mechanism from the forest itself – rainfall within the Amazon basin depends on intact forest; it rains less where there has been massive deforestation. Heard about tipping points? There’s a big field experiment going on to find out which massive new soybean/sugar cane/oil palm biofuel crop in Brazil will be the one that turns off the Gulf Stream. Not to mention the toucans.
Dr. Sara Bennett
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