No, birds are not mammals. Rather, they are avians. Mammals are characterized by their milk glands, hair, vertebrae and their birthing of live young (being viviparous), according to Britannica.

Principles of taxonomy -- Formal classification of mammalia -- Review of mammalian classification -- Bibliography -- Index to technical names -- Index to vernacular ...

A REMARK made by Prof. Allen Thomson on this subject in a late number of NATURE induces me again to draw attention to some objections I offered to the placental classification in a review of Prof.

National Geographic estimates there are between 50 billion and 430 billion birds populating the planet, outnumbering humans by up to approximately 50 times. Spread across 9,700 species, according to ...