Which is the smallest bird?

The bee hummingbird, native to Cuba, is the smallest bird on Earth, measuring just 5 to 6 centimetres long and weighing under 2 grams — lighter than a coin. It is so tiny it is often mistaken for a bee, which gives it its name. Its wings beat around 80 times per second, allowing it to hover and even fly backwards, and its heart can beat over 1,000 times a minute. To fuel this frantic pace, it must feed on nectar almost constantly.