The Cockatiel is the smallest cockatoo endemic to Australia. The Cockatiel's distinctive erectile crest expresses the animal's state of being. The crest is dramatically vertical when the cockatiel is startled or excited, gently oblique in its neutral or relaxed state, and flattened close to the head when the animal is angry or defensive. The crest is also held flat but protrudes outward in the back when the cockatiel is trying to appear alluring or flirtatious. They are prized as a household pet and companion parrot throughout the world and are relatively easy to breed. As a caged bird, cockatiels are second in popularity only to the Parakeet. The Cockatiel's lifespan in captivity is generally given as 15–20 years.