It is generally accepted that Archaeopteryx was the world's first bird, though it was really nothing more than a lizard with feathers. As far as we can tell it was the first creature ever to be covered with feathers and, although primitive in form, these gave two advantages; firstly allowing a better control of body temperature, and secondly offering possibilities of flight. Both these factors made the animal more versatile and adaptable in its environment than its ancestors.
Remains of Archaeopteryx from limestone beds near Solnhofen, Bavaria, dated some 150 million years old, show that claws on the forelimbs were well developed, suggesting that this first bird may have been partly arboreal, using all four limbs for climbing, then spreading the wings to enable it to glide from tree to tree.
These thoughts were very much in my mind while I was seeking out a bird which is about the nearest one can get to a living Archaeopteryx, surviving today in the swamps of the Orinoco basin of South America. It is a bird as strange and bizarre as its name, hoatzin, and has succeeded in foxing zoologists for years as to the origins of its odd characteristics. Unable to decide whether it is truly primitive or just an evolutionary throwback, scientists have shelved the problem and placed the hoatzin, Opisthocomus hoazin, in a family or even an order all by itself.
Many features distinguish the hoatzin from other birds, not least of which is its voice which sounds more like a heavy smoker's wheezing than a bird call. About the size of a rather slender, upright pheasant, the hoatzin has an untidy crest of feathers, blood-red eyes encircled by bright blue skin, a long neck and long tail feathers. But perhaps the most interesting characteristic is the presence of claws on the wings and these, although useless to the heavy adult bird, are employed by the youngster to clamber among the branches near the nest- just as Archaeopteryx must have done so many millions of years ago.
The main function of the wing claws, it seems, is to assist the young hoatzin in times of crisis. The nest is normally built on branches overhanging water and is thus exposed to the eyes of marauding hawks. It is a rudely constructed platform of short twigs of roughly pencil thickness. If danger threatens, the parents usually abandon the nest for the safety of dense bushes nearby. The chick, left to its own devices, either uses the wing claws to help it clamber through the branches to some inaccessible spot, or dives into the water and emerges farther downstream to clamber back to 'the nest once the danger has passed.
Tomas Blohm, a well known conservationist in Venezuela, told me that there were hoatzins on his ranch in the llanos, the flat prairie lands which fringe the Orinoco river, and he kindly suggested that I use the ranch house as a base for filming excursions. Unless it had rained heavily, it was easy work in a four-wheel drive jeep to explore the flat ranchlands and always interesting too, for the animal life is extraordinarily rich in these areas. The hoatzins were to be found on the far side of the ranch in bushes along Canal Caracol, a winding tributary of the Rio ,Guarico which flows southwards to swell the Orinoco.
For the first few days, my approach at dawn was heralded by wheezing sounds and laboured flurries of wings as the hoatzins made off to crash-land in bushes deep in the swampy thicket: hoatzins are weak fliers. I was lucky to find a nest, freshly built, and over a period of only two days, first one, then two, and finally three eggs appeared, each about two inches long and pale in colour, covered in light brown speckles and blotches. Of standard clumsy construction, the nest was situated in an exposed position over the water.
The incubation period lasted 28 days and during this time the parents became quite used to my arrival and presence. A hide was never necessary; on the contrary. I was eventually able to climb into the bush and sit on a forked branch not four feet from the nest while the male and female hoatzins, which were indistinguishable from one another, took turns in sitting. During the day the incubation process was not so much one of keeping the eggs warm but cool and protected from the fierce rays of the sun. The parents had refrigeration problems themselves and 'would continually pant in order to keep cool.
Changing the guard took place twice during a twenty-four hour period and was something of a ritual, preceded by expectant honking grunts from the sitter as the other bird crash- landed on a nearby branch. Place changing was rapid and it was necessary to watch very closely indeed to see that all three eggs were still intact. With the nest in such an exposed position it was important for the parents not to leave it unattended for a moment; hawks and vultures were constantly parading the sky, in their never-ending surveillance of possible prey.
The twenty-eighth day duly arrived and during the heat of the afternoon I noticed from my arboreal perch that the sitting parent was making uneasy shifting movements. and from time to time would raise itself slightly to examine the eggs. A sign I thought that hatching was about to occur -and sure enough, at dusk a tiny black fluffy head poked out from under a wing.
At dawn the following morning there were two hatchlings and. by midday, all three had made it. The first was already being fed by the adult with regurgitated leaves with a colour and consistency of pea soup. After two more days. the chicks were beginning to wander to the edge of the nest using the wing claws as a second pair of feet to grasp their way across the twigs. My intention was to make a photographic record of the young using the wing claws, something that seems never to have been successfully achieved before, and now that prospect seemed guaranteed with the family of tame hoatzins at my feet.
It all seemed too good to be true -and my arrival at dawn on the third morning after hatching confirmed it. Disaster had struck -the chicks were gone, the nest was destroyed and the parents were sitting on a branch close by in a state of bewilderment. It was impossible to speculate on exactly what had taken place; there were, as usual, several birds of prey in the vicinity.
The perfect opportunity to record the family development lost, I started to search for other nests, at last finding two, both with eggs. The original pair made a feeble attempt to rebuild their nest but eventually abandoned it for an altogether better site in a more inaccessible spot under the shelter of a large tree. Some days later I was pleased to witness them mating to begin the whole process over again. There is no fixed season for reproduction; although it seems to reach a peak at the beginning of the rainy season in July and August, pairing and nesting maybe observed at almost any time of year. There also appeared, at least at this site, to be a very high rate of predation making a continual reproductive season necessary, for the other two nests I had discovered with eggs were themselves destroyed even before hatching had taken place.
A search in a completely new location about a mile downstream revealed two nests in session; one with eggs and one with a single large chick. A colleague in Guyana had once told me that chicks remain at the nest for about three weeks; this one must have been at least two weeks old. Anxious to witness the defence behaviour and climbing, I tried to elicit a response by approaching the nest. The parents, at first, did not fly off but took up positions on either side of the chick in an attempt to hide it from me. As I came closer, however, with a shambolic flapping of wings they crossed to the far side of the river. The chick, now alone, clambered away from the nest but it was obvious that it was already too heavy to rely entirely on the wing claws, and it made an ungainly compromise between using the wings as grasping arms and as conventional wings. Although the nest had been built .over the water, the chick made no attempt to dive into it; a wise decision I decided, judging from the number of Cayman in the water.
If this chick was already too old to demonstrate the use of the wing claws then the ability may only be utilised during a period of two weeks or less of the hoatzin chick's lifetime, an insignificant term to earn it such a reputation, but perhaps the survival of this species is directly due to this curious adaptation. For me, the filming of the crucial period of the chick's life will have to wait until another time.