|Subtropical Rainforest, Iguazú National Park|
Which are the birds which can
be observed in a greater number
and with a greater frequency all
year round in a tour through the
Iguazú Waterfalls Circuits?
Without any doubt: the Swifts,
who at first sight resemble swallows.
They have a small and aerodynamic body, very short
legs and long, narrow and pointed wings.
These indefatigable fliers hunt insects and even small spiders in the air with their big mouth and small beak. While they fly they can mate or take materials for their nests, such as feathers or pieces of moss in suspension. They mate in the hollows of basalt where they make their nests, as is the case of the Great Dusky Swift.
They do not perch on branches or on the ground, but they can be seen on the rocky vertical walls, which they catch on to by their nails and they find support with the callosities of their tarsals and their rigid tail. They build their nests by sticking them with saliva on cavities or projections of rocky walls.
The most common species in Iguazú is the Great Dusky Swift, with greyish-brown plumage. The National Park is one of the few nesting places of this species in Misiones.
It is possible to observe the Great Dusky Swift at rest from the paths of the Lower Circuit. You have to look between the rocks of the Alvar Nuñez Cabeza de Vaca Fall, in the Dos Hermanas Fall or in the walls of the Bossetti Fall.
It has been proved that on rainy days they remain in their resting places, while on sunny days they start their activity very early. In the area of the Devil’s Throat they can form flocks of up to 3,000 individuals.
In the Falls of greater volume of water, it is surprising to see how they appear and disappear behind the curtain of water in their fast flight while passing through clearings or gaps.
They usually build their nests behind the waterfall, safe from their predators. Although not all is a “rose in the garden of Eden”, sometimes “thorns” are felt. In Brazil there are reports of swifts which have been trapped by the waterfalls, suffering injuries or even death.
It has also been suggested that the laying of few eggs and the long incubating period are a consequence of the low temperatures and high humidity their nests are exposed to. An adaptation to this is the protective plumage the fledglings of some swifts acquire.
The Ambay is one of the nearly 50 species of the genus Cecropia found in Central and South America. It belongs to the family Moraceae, as does the Guapoy.
Cecropias are one of the first trees which grow in the gaps which appear in the jungle or in the banks of streams; and -after the action of man-, in deforested areas, or at the sides of roads. They are coloniser species or pioneers.
In the area of the Waterfalls, in the Iguazú National Park, the Ambay is one of the most common trees.
They have a straight trunk with hollow compartments separated by partitions. They branch up high to form a wide treetop and they posses very few plants growing on their trunk (lichens dominate). They do not spend energy nor raw matter to synthesise toxins against herbivores (they have latex, a characteristic of this Family).
Their large and parasol-like leaves need to be exposed in gaps with good light. The fertilised flowers produce an impressive number of seeds (in some species up to 900,000 seeds per plant in each fruit), giving small fruits quite frequently.
Don’t these characteristics show us some type of strategy?
It seems that all the energy of the tree is used to obtain a fast growth and dispersion, typical of the coloniser species.
A sample of Cecropia of a tropical species grew five meters high in only one year. Yes, five meters in only one year!
Another noticeable feature of the Cecropia is that Aztec Ants (genus Azteca) live in its hollow trunk. These aggressive ants defend their territory, in this case the tree, against several herbivores, for example Leaf-cutter Ants. In exchange they obtain refuge and food from the extrafloral nectaries, a type of “gland” which produces nectar, found in the axils.
A great concentration of these ants can represent a disadvantage as it means a tempting banquet for predators such as woodpeckers. It is also possible that ants are not such an efficient means of defence as would be the chemical toxins produced by other plants. This is the reason why in some Cecropia the leaves can be affected by herbivores.
If you stop in front a sample of Ambay you may see it for yourself. The extrafloral nectaries and the small holes through which ants enter the hollow trunk are visible. If the tree has fruits and you can hide somewhere close, with a little patience you might observe different birds, such as Plush-crested Jays, tanagers, euphonias, or even a toucan, in search of food.
Source: Santiago G. de la Vega, 1999. The Laws of the Jungle, Contacto Silvestre ediciones.
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