In terms of typical body weight, the heaviest flying bird is the Cory bustard, weighing 11 to 19 kg, followed by the great bustard (6 to 18 kg), the mute swan (6 to 15 kg) and the Andean condor (up to 15 kg ). Due to their huge weight, bustards consume a lot of energy when flying, so they only take off when necessary.
The theoretical limit for maximum body weight for horizontal powered flight is between 10-15 kg. This means that, technically speaking, the largest male bustard is already bigger than it should be!
