Mother nature and her bag of tricks

by Jack Ewing

For as long as I can remember nature lovers have used the term "natural balance," the meaning of which has always seemed so clear that there was never any thought of analyzing the concept. I have used the term countless times in these articles and never felt the slightest need to elaborate on the meaning. But a few months ago a tiny inkling of an idea germinated in my mind, took root and grew, bringing with it a number of questions: How can we determine when nature is in or out of balance? What causes nature to get out of balance? When nature gets out of balance, what happens? How do humans affect natural balance and how does it affect us? Let's have a closer look.

Thirty-five years ago, a large part the land that is now Hacienda Barú National Wildlife Refuge was treeless pastures and farm land. About 150 hectares of rainforest and 20 hectares of mangrove were the only areas that could be considered untouched. Throughout the central pacific region dry season burning of recently felled forest, chopped pasture and rice stubble were common practices. Sometimes the clouds of smoke lowered visibility to the point that small planes were warned to stay away. Looking at old aerial photographs of this area makes me wonder how the land could have survived such devastation and still retain the resilience to rebound into the tropical paradise that we find today.

Yet, at that time, it never occurred to those of us who lived here that nature was out of balance, and we may have been right. Thinking back on it I remember that squirrels, coyotes and white-tailed deer were a common sight. Bird watchers could easily observe black-shouldered kites, large flocks of gray-headed chachalacas, smooth-billed anis, northern jacanas and variable seed eaters. Herpetologists could appreciate the presence of the mussurana snake and an abundance of both green and black iguanas. But after 25 years of regrowing the rainforest, five of these once common species have disappeared from Hacienda Barú National Wildlife Refuge, and the rest have become quite scarce.

You might think that by restoring rainforest to denuded lands we should gain species not lose them. After all, rainforest contains much more biodiversity than pasture or fields. However, we started with about half rainforest and the other half evenly divided between pasture and fields, and ended up with 95% rainforest. So it is only logical that we would lose the species that thrived in open spaces but not in forested habitat. In most cases the species that declined weren't lost, they simply migrated to areas where their preferred habitat exists, or remained here in smaller numbers.

At Hacienda Barú the natural restoration process began in 1979 on a steep hillside pasture of about 30 hectares (74 acres.) In the low lands, living fences were used by arboreal wildlife as corridors between patches of forest. Eventually we began converting lowland pasture and rice fields to secondary forest. As Mother Nature reclaimed the land, natural vegetation took hold and eventually secondary tropical wet forest returned. At the same time, we observed changes in the prevalence and types fauna. However, the situation was atypical. Normally when human populations increase, forest cover decreases, but ecotourism became a driving force that reversed that trend. Visitors to the region preferred seeing monkeys and toucans rather than pasture and rice fields. With new roads, bridges, electricity, telephones, etc. came people, and while the jungle returned, the total amount of wildlife increased. By this I mean that populations of many of the rainforest species increased; there were more monkeys, more toucans, more coatis, more pacas and more peccaries, for example. But in the final count there were less species. Some animals and birds lost their preferred habitat, some gained. Those that gained often adversely affected those that lost. And to further complicate things, there were people.

The green iguana is an example of a species that diminished markedly. This was partly because of habitat loss, but more importantly because of predation by species that thrive in a forest habitat. Early in the cycle of forest regeneration, populations of the white-nosed coati experienced a rapid increase at Hacienda Barú. Coatis are omnivorous and, in addition to fruit, they feed on grubs, insects and small invertebrates which they catch, dig up from the soil and tear out of rotting logs. Female iguanas share the work of excavating in soft soil to create a communal burrow about one meter deep, in which they lay their eggs. Digging out the nutritious iguana eggs is hard work, but still a feasible task for a large group of coatis. And their numbers reeked a terrible toll on the iguana population.

But the large green lizards had more to worry about than just coatis. Rapidly growing secondary forests, replete with fruit bearing trees, are like a candy store for white-faced capuchin monkeys which, like the coatis, increased in population. But fruit isn't the monkey's only food, and juicy, protein-rich iguana meat is a welcome change of fare for these omnivorous primates. White-faced capuchin monkeys aren't, however, partial to iguanas and will eat any meat they can catch and kill. Coatis build nests for rearing their young in trees where they are safe from many predators, but not from capuchin monkeys that kill and eat all the coati babies they can find. Growing monkey populations put pressure on the coatis, whose numbers gradually diminished to a level where they were no longer a serious threat to iguanas.

A decrease in predatory birds further favored the iguanas. The reproductive cycle of many hawks, kites and falcons is synchronized so that the young are fledged about the same time as baby iguanas hatch and emerge from their underground nest. The young birds, awkward hunters at best, would likely starve without this convenient source of equally awkward prey. But most raptors need open space to hunt, so their numbers diminished as the forest returned, and this was good news for the iguanas. Overall, green iguana numbers have diminished by about 90% since the rainforest restoration cycle began. The present population remains stable, but they mostly inhabit forest edges and islands of trees in open areas where monkeys are less likely to find them.

Let's have a look at a formerly abundant raptor, the black-shouldered kite, which was truly mesmerizing to watch. These slim, streamlined, black and white hunters were often seen hovering in the wind, body in a vertical position and wings fluttering. I have seen them remain in that position for a minute or more finally plunging all the way to the ground and returning to the air with a rat or lizard grasped between powerful talons. However, I haven't seen a black-shouldered kite in more than ten years, and I attribute their demise more to an unfortunate behavioral attribute than to habitat change. In 1986 when electrical service became available in this region, black-shouldered kites discovered that the cables were a perfect place to perch. Unfortunately for the birds, improved roads accompanied the electricity, and roads bring people. Many delivery trucks with products for small general stores began making regular weekly visits. A number of the drivers fancied themselves as hunters and carried rifles in their trucks. They killed everything they saw, and shooting black-shouldered kites perched on electrical cables was like catching fish in a barrel. In less than a year these beautiful birds disappeared from this region. Those species of hawks, kites and falcons that thrive in a forest habitat have increased, and the prairie hunters have diminished to a fraction of their former numbers. Only the black-shouldered kite has completely disappeared.

The mussurana snake, famous because its diet consists almost entirely of venomous pit vipers, has all but disappeared from this region. The mussurana thrives anywhere that pit vipers lurk, and these are found both in open space and forest. The mussurana's downfall is that it crawls very slowly, a fatal defect when roads improve, bringing more and faster moving vehicles. When this region had only jeep trails and few vehicles, mussuranas were common. A large mussurana lived near our house and kept the poisonous snakes in check, but I haven't seen one in more than ten years.

Now that Hacienda Barú National Wildlife Refuge is almost entirely forest we are seeing many animals like collared peccaries, great curasows, white-necked puffbirds, two species of sloths and others in parts of the refuge where they hadn't been sighted until recently -- those places that have been newly restored. The Central American spider monkey, migrated along biological corridors formed by newly restored secondary forest on neighboring properties and arrived at the refuge in 1997. A small troop now resides and reproduces here. Hopefully, other species will come with time.

With all this in mind let's go back to our original doubts about natural balance. In spite of extensive deforestation and burning it appears that there were more species -- at least the larger and more visible ones -- here in the 1970s than now. Does that imply a better natural balance at that time? Is nature out of balance now? Was nature out of balance while forest was regenerating? I think the answer is that nature was always in balance. I believe that the cases we have examined are simply examples of a few of the natural mechanisms that bring creatures closer to a state of equilibrium. Nature is dynamic, and as conditions change, relationships amongst species also change, but natural balance isn't lost. Only something catastrophic -- a collision with a large meteor or an enormous volcanic explosion -- could cause that, and even then Mother Nature would eventually reclaim what has always been hers.

When the coatis were reeking havoc on iguana populations, you may have noted that it was the monkeys that brought them back into line. Now it is the monkeys that are having a negative effect not only on coatis, but also on iguanas, squirrels and some bird species. I can't help but wonder what trick Mother Nature will pull out of her hat in order to bring the monkeys back into line, and how far she will let them go before deciding to yank the rug out from under them. As harmful as the monkeys have been to other wildlife, their prey species were never completely annihilated and are still found here, albeit with much lower populations and in a smaller niche.

In the case of the black-shouldered kite and the mussurana, humans completely eliminated them from this region as we did earlier to tapirs, jaguars, white-lipped peccary, scarlet macaws and harpy eagles, and as we are doing on a planetary scale with tigers, orangutans, snow leopards and pandas. Worldwide, human populations have more than doubled in less than half a century at the same time that exponential advances in human technology have allowed us to do more damage to the natural systems of the planet than any other species in the history of life. I wonder what Mother Nature will pull out of her bag of tricks to bring us back into line? Climate change? Disease? Our own toxic waste? Maybe we should consider using our intelligence to create technology that will lower our impact on the rest of life. There is probably still enough time.

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Focussed in Birdwatching Costa Rica and Ecotourism