What ways are there for a black hole to lose its mass?

Question

How can a black hole lose its mass? Is Hawking radiation the only way?

Answer 1

Hawking radiation is not the only way. Mass can also be lost in the form of gravitational waves since it takes energy to create these waves and energy is directly proportional to mass (times $c^2$).

Also note these waves are created in the event of two black holes spiraling and colliding with each other.