Swallows are a large family of passerine birds in the family Hirundiniae. They are perhaps most famous for their seasonal mass migrations, which include scores of birds which often travel between continents. Swallows can be found all over the world, and many cultures have specific myths and legends which pertain to swallows. Many communities, for example, view swallows as good luck, and destruction of their nests is viewed as unlucky, especially for farmers with livestock.
The term "passerine" is used to encompass a huge order of birds. Passerines are incredibly diverse, coming in a range of sizes, shapes, and colors. Many people call them "songbirds," although not all passerines sing. They are perhaps better known as "perching birds," because they have special adaptations which allow them to perch, including a unique backward-facing toe which assists them in gripping branches.
A typical swallow has a streamlined, muscular body which is built for flying, with dark plumage which may be marked with iridescent accents. These birds classically have pointed wings and notched or forked tails which create a very distinctive silhouette in the air as they fly. Swallows are also famous for their large mouths, designed to help them quickly and efficiently catch insects while in flight. Baby swallows tend to be dwarfed by their mouths when they open them, creating a very comic appearance.
Many people are familiar with barn or cliff swallows, who like to build their nests in eaves and rafters of human constructions. Swallows may also nest in trees, and in all cases, they build mud nests which are extremely strong and well insulated. The parents typically cooperate to raise their hungry young, and the birds are monogamous, establishing breeding territories which they return to again and again.
There are least 100 known swallow species, making these birds quite diverse. Depending on the species, a swallow can produce a variety of vocalizations, ranging from cheeps and peeps to true birdsong. Male swallows often sing to attract mates in the spring. Many people view swallows as signs of seasonal change, since they return to northern climates to mate and raise their young in the spring and fly south in the fall.