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Which hummingbird is the smallest living bird?

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Illustration of a chestnut-collared swift (Cypseloides rutilus) in flight, showing its dark brown body and wings with a distinctive reddish-brown collar around its neck. — Apodiform Chestnut-collared swift (*Cypseloides rutilus*)

The bee hummingbird (Mellisuga helenae), native to Cuba and the Isle of Pines, is the smallest living bird in the world.1

Measuring slightly more than 5.5 cm (2.2 inches) in length and weighing approximately 2 grams, this species is considered one of the smallest warm-blooded vertebrates. It is a member of the family Trochilidae, which is part of the order Apodiformes.12