|
Smart Cetaceans
Dolphins have been popular with
humans since ancient times due to their astonishing
ability to learn and their extraordinary behaviors.
But while they are admired by young and old alike,
they suffer the impacts of human activities and are
not strangers to the threat of extinction.
There are 70 species
listed in the suborder of cetaceans known as 'Odontoceti'
in the classification of animals. More informally,
these are "whales with teeth", and cover
all sea- and river-dwelling dolphins.
According to information
found on the Internet, there are some 30 ocean dolphin
species and five river dolphin species.
Dolphins are mammals, meaning
mothers nurse their young, and are the result of a
long process of evolution, which experts say began
with creatures that lived on land. An important trait
of this group of species is that, unlike fish, and
like their cousins the whales, dolphins must breath
air.
These excellent swimmers can
reach speeds of 40 km per hour. They also possess
a sophisticated sonar system that allows them to locate
objects in the water around them.
But one of their most astonishing
characteristics is the relatively large size of their
brains, which determines intelligence. Dolphins are
naturally curious and can easily learn behavior taught
by humans.
The survival of dolphins, however,
is at risk. Many fall victims to fishing nets, a problem
that is the focus of several conservation
campaigns worldwide. There is also a great deal of
criticism about keeping these extremely intelligent
animals in captivity
and using them in marine shows or in experiments.
Species
of Dolphins
International
Dolphin Conservation Program
Thinkquest:
Dolphins (educational)
Discovery
Channel: Dolphins
FAQs
about Dolphins
Similarities
between Humans and Dolphins
Greenpeace
Foundation: Dolphin-safe campaign
Delicate Avis
The hummingbird is known by several
names in the Western Hemisphere: colibrí, picaflor,
and beijaflor, but its scientific name is Trochilidae,
and it is a wonder of nature in the Americas.
When the first Europeans arrived
in the New World, these tiny birds amazed them. At
first they confused them with giant insects, because
of their buzzing of wings and their dedication to
flowers, which provide their sustenance.
These tiny wonders captivate
the human imagination, leading people to come up with
ways to attract the birds to artificial nectar feeders
to get a closer look at them. In the United States,
it is illegal to keep hummingbirds
as a pet.
The Trochilidae
family is exclusive to the Americas, and its members
can be found from Alaska to Tierra del Fuego, with
328 different species recorded.
At websites
dedicated to this bird, we find that the largest weighs
20 grams and lives in South America, while the smallest
is just 2.2 grams, and is native to Cuba. One of the
most interesting hummingbird cases is that of the
Chilean island of Juan
Fernández, which has its own unique species
that is not found outside this island 600 km from
the coast.
The flight of the hummingbird
is awe-inspiring. The beating of the wings is so fast
that it is nearly impossible to see the single movement.
They can fly at high speeds, but also carry out such
feats as flying in place and backwards.
These abilities mean that the
hummingbird has an accelerated metabolism and must
consume great quantities of energy. The bird must
drink lots of water and feeds an average of 300 times
a day. The human equivalent would be to eat 130 kilos
of bread and drink 150 liters of water each day.
These "miniscule and sensitive
birds" play an important role in the ecosystem
as well, contributing to the pollination of plants.
The
Hummingbird Web Site
Kolibri
(Hummingbird) Homepage
Hummingbirds.net
Hummingbird
websites
The
Hummingbird Society
Hummingbirds:
featured on postage stamps
The Rivers Flow
Rivers are an unequivocal synonym
of life. Their flows sculpt the land's geography,
determine the traits of ecosystems and guide the settlement
of civilizations. But in spite of their transcendent
role, many rivers are in danger.
Nearly all rivers have characteristics
in common. They originate from a water source, at
a higher elevation, and follow a route that the water
has traced over time, with the volume of water increasing
as tributaries join the flow.
Rivers are a necessary source
for freshwater, which supports life. The area of influence
of a river is known as its basin, the preservation
of which is a top priority for those who seek to protect
ecosystems.
Throughout history, rivers have
been very important for human civilization, which
is why major cities and cultures have flourished along
their banks. However, these water sources have
been affected by our presence on Earth.
We humans produce pollution and
our development projects change the course of river
flows. One of the most conflictive situations involves
the tens of thousands of dams,
which are capable of ending the life of a river.
The Internet
reveals a great deal of information about rivers,
much of it provided by organizations
dedicated to conserving
these flows of fresh, live-giving water.
Portal:
International Rivers Network
Thinkquest:
All along a river
Principal
rivers in the world
BBC:
Rivers in danger
National
Geographic: Rivers 2001
Yahoo!:
websites about rivers
World
Commission on Dams
|
