Vespertilio

The Vespertilio, also known as Chauve-souris is a bird that gives birth to living young.

General Attributes:

The Vespertilio is not a noble bird. It is unlike other birds in that it gives birth to live young instead of laying eggs, and it has teeth. The Vespertilio gather together and hang from high places like a bunch of grapes; if one falls, all the rest also fall.

Sources (chronological order):

Pliny the Elder [1st century CE] (Natural History, Book 10, 81): The Vespertilio is the only flying creature that bears live young and feeds them with its milk; it also carries its children in its arms as it flies.

Isidore of Seville [7th century CE] (Etymologies, Book 12, 7:36): The Vespertilio, unlike other birds, is a flying quadruped, resembling a mouse. It has its name (vespertilio) from the time when it flies, after twilight. It flies about driven by precipitate motion, hangs from fragile branches, and makes a sound like a squeak.