Bestbirdguide
No, You Birds are not mammals as they belong to a different class called Aves, which is related to reptiles rather than mammals.
Mammals have a different class called Mammalia.
Coming to the fact, mammals are the only animals having hair whereas birds are the only living animals having feathers.
Both have a sophisticated and complex respiratory system with lungs
Both have a four-chambered heart which means their hearts consist of a right and left atrium
Birds belong to a whole different class of animals called Aves.
Birds belong to the class Aves, not the class Mammalia to which all the mammals belong.