Geoscience Reference
In-Depth Information
hunted in the i rst half of the twentieth century
and was on the brink of extinction. Protective
hunting laws in the 1960s and trade restrictions
in the 1970s along with captive and wild sus-
tainable harvesting have led to a dramatic recov-
ery, so that now millions of American alligators
survive in the wild (Britton 2009a). Similar
conservation efforts are underway for other
crocodilian species in many other countries,
but enforcement is difi cult, and poaching and
habitat destruction continue to impact these
animals in many parts of the world.
Figure 7-17.
American crocodile (
Crocodylus acutus
)
displaying the long, narrow snout and interlocking
teeth that distinguish it from the alligator. Adapted
from Everglades NPS
7.3.3 Birds
<
http://www.nps.gov/ever/
parknews/evergladeswildlifeimages.htm
>
.
For many people, birds are the most obvious
and attractive wildlife in wetlands
-
thousands
of birds, millions of birds. The sheer number of
birds and diversity of species demonstrate the
biological richness and productivity of wetlands.
At Tule Lake in California, for example, as many
as four million birds may be present at one time
during migration season on the Pacii c l yway
(Niering 1985). At the Laguna Atascosa National
Wildlife Refuge in southern Texas, more than
400 resident and migrant bird species have been
recorded (Fig. 7-18), the most of any national
wildlife refuge in the United States (U.S. Fish
and Wildlife Service 2009a). Nearly all bird
species may visit wetlands occasionally to take
advantage of food, protection from predators, or
nesting (Fig. 7-19). Among these, some species
are adapted specially for wetlands through their
morphology or behavior.
Waterfowl and shorebirds comprise many
species, genera, and families of birds that inhabit
wetlands for most or part of their seasonal and
life cycles. Ranging from the mouse-sized least
sandpiper (
Calidris minutilla
) to the great blue
heron (Fig. 7-20), these wetland birds have
diverse bodies, behaviors, food and habitat
requirements, life cycles, and migratory pat-
terns. Waterfowl include those birds that typi-
cally swim or dive, such as ducks, geese, swans,
coots, pelicans, grebes, teals, cormorants, and
many other types. Shorebirds, on the other
hand, walk on beaches, mudl ats, sand banks
and wet meadows or wade in shallow water.
Herons, egrets, cranes, ibises, sandpipers, terns,
are native only to India and the Malay peninsula.
Most crocodilian species cannot tolerate tem-
perature below
∼
10 °C (San Diego Museum of
Natural History 2010), although the American
alligator (
Alligator mississippiensis
) may survive
short-term freezing conditions if it is in water
underneath ice (Britton 2009a).
Crocodiles and alligators inhabit primarily
fresh-water lakes, rivers and swamps, as well
as brackish lagoons, estuaries, and mangroves.
Some species, such as the American crocodile
(Fig. 7-17), tolerate marine water and may
venture far offshore. The American crocodile is
found also in hypersaline lakes, such as Lago
Enriquillo (Dominican Republic), in which salin-
ity may reach 100‰: three times normal marine
salinity (Britton 2009b). Crocodilians are, in
general, opportunistic eaters that take any avail-
able prey or carrion appropriate to the animal's
size (juvenile or adult). The American alligator
may scoop out so-called gator holes in soft soil
during drought episodes. These depressions
become miniature marshes in which many other
wetland plant and animal species take refuge
during the dry period (Niering 1985). Alligators
and crocodiles occupy the top of the food chain
in many wetlands; thus, they serve key roles
for controlling animal populations and creating
microhabitats with their nests and gator holes.
The main threats to crocodilians are habitat
destruction and hunting for their valuable skins.
The American alligator, for example, was heavily
