Passerines, members of the order Passeriformes, are also known as perching birds. They make up the majority of bird species.
There are about six thousand species of passerines.
Passerines can be found on every continent on Earth except Antarctica.
The word passerine comes from Latin, and means "like a sparrow."
Passerines tend to be small.
Their feet are adapted for perching, with three toes in front and one toe in back, a condition known as anisodactyly.
The passerine wraps its toes around its perch - a tree branch, for example.
Passerines often have strong, sharp claws that help them to grip their perches.
If a passerine starts to lose its grip, its leg muscles will automatically contract. This allows it to sleep on its perch.
Ornithologists believe that passerines evolved from a common ancestor that lived on Earth about 60 million years ago. This common ancestor lived on the continent of Gondwana (Gondwanaland), which later became Antarctica, Africa, Australia and South America.
Many passerines are known as songbirds because they produce distinctive songs that human beings often find beautiful.
All birds have a vocal organ known as a syrinx.
It is located at the base of the trachea (windpipe), where the trachea forks into two branches leading to the bird's two lungs.
Because its syrinx is divided into two branches, a bird can produce two sounds at once.
Songbirds have powerful muscles for controlling their syrinxes.