What is the adaptive advantage of rattles on a rattlesnake?

The sound is startling to most vertebrates with ears. Predators are first startled then presented with a defensive posture. Many other snakes, even harmless ones will rattle the tail in dry leaves to make the same sound. read more

Every time the snake sheds its skin, another one of these loose remnants of hard keratin gets added to the chain that are already stuck on, forming the rattle. When the snake vibrates its tail, these loose, individual pieces knock against each other, producing the rattling or buzzing sound. read more

It turns out that rattlesnakes that rattle are more likely to be killed by humans. As a result, rattlesnakes that lose their ability to rattle are more likely to survive. More of them are reproducing and passing their defect on. read more