using their powerful legs and talons to subdue snakes
and small mammals. Besides their unique ecology,
perhaps the most distinctive aspect of the seriemas is
their ancestry. Anatomical and genetic analyses strongly
indicate that they are direct descendants of the flightless
so- called terror birds (Phorusrhacidae), which were top
carnivores in savanna ecosystems throughout much of
South America during most of the Cenozoic era.
The largest birds of the cerrado are the flightless
rheas, relatives of the ostriches. There are two species,
the widely distributed Greater Rhea (Rhea americana;
plates 14- 13– 14) and the more southerly and less
widely distributed Lesser (once referred to as Darwin’s)
Rhea (Rhea pennata). The Greater Rhea is the larger
and more abundant of the two. Rheas have the unusual
habit of laying eggs in a communal nest. Several females
mate with one male, and each hen deposits two to three
eggs in the same nest. Only the male incubates. Rheas
have adapted well to human agricultural ecosystems in
cerrado areas and are commonly observed as roadside
birds.
Caatinga
Caatinga is a more desertlike ecosystem scattered
throughout parts of Brazil, consisting of highly seasonal
(with prolonged dry season) deciduous forest dominated
by spiny trees and shrubs with thick leaves and thick
bark, their branches covered with an abundance of
lichens and mosses. Various cactus species occur in
caatinga, and many plants are widely spaced on the
dry soil. Caatinga occurs in climate that could support
forest were it not for the nutrient- poor, sandy soil plus
a marked seasonality in precipitation. This ecosystem
is not nearly as diverse as moist forest but nonetheless
is characterized by a unique array of trees, grasses, and
sedges, many of them endemic to the region.
Thornwoods
Thornwoods occur in semidesert areas from Mexico
through Patagonia (plate 14- 15). Dominant trees are
usually Acacia species and other leguminous trees, of
short stature, spaced well apart, and often interspersed
with succulents such as cacti and agave. In many
areas of thornwood, large herds of goats can be seen
wandering about. Thornwood is very common along
the Pan- American Highway throughout Peru, as well
as in central Mexico and many West Indian islands.
Examples of Tropical Wet Savanna
Los Llanos: Seasonal Savannas of Venezuela
and Colombia
The wide floodplain of the Orinoco River extends over
an area of grassy savanna interrupted by riparian forest
and hammocks of woodland (raised areas in otherwise
marshy areas). This habitat is called the Llanos (plate
14- 16). It bears a strong physical resemblance and
ecological similarity to the Florida Everglades, being
essentially wet tall- grass prairie with grasses growing
up to 1 m (3.3 ft) in height. The Llanos extends for
an area of approximately 100,000 km^2 (38,610 mi^2 )
throughout southern Venezuela and into parts of
Colombia. Grasses and sedges, especially those in
the genera Panicum, Leersia, Eleocharis, Luziola, and
Hymenachne, dominate much of the landscape. Trees
and shrubs are widely scattered, often occurring as
“island” woodlots called matas or bancos. These small
and scattered woodlots are also known as hammocks,
especially in the Florida Everglades.
The Llanos is seasonal wet savanna, with pronounced
dry season extending through most of the northern
winter. Approximately 100 cm (39 in) of rain is received
over the seven- month rainy season. But for nearly five
months, rainfall is quite low. It is then when natural
fires are common. During dry season, vast flocks of
wading birds such as ibises, storks, herons, and egrets
are concentrated in the relatively limited remaining
wet areas. These birds, plus the added presence of such
species as the Capybara (Hydrochoeris hydrochaeris;Plate 14- 15. Thornwoods are common in more arid areas in
the Neotropics. Photo by John Kricher.256 chapter 14 don’t miss the savannas and dry forests