Rattlesnakes are venomous snakes, immediately recognizable by the distinctive structure at the end of their tails. This structure, known as a rattle, serves a primary role in communication. Understanding the rattle’s structure, function, and development is central to comprehending their biology.
The Rattle’s Warning Purpose
The rattle’s main function is an auditory warning signal, deterring threats. Rattlesnakes use this sound to alert large animals, including humans, preventing accidental trampling or confrontation. This behavior is defensive, indicating the snake’s preference to avoid physical engagement before striking. The rattling serves as a clear signal to “stay away,” conserving the snake’s venom for prey capture rather than defense.
This defensive display is a form of acoustic aposematism, where an animal signals its potential danger. While the sound warns larger creatures, rattlesnakes do not rattle when hunting, as that would alert their prey. The ability to rattle allows them to avoid costly encounters, as venom production requires significant energy.
The Mechanics of Sound
The rattling sound originates from hollow, interlocking segments at the tail’s tip. These segments are made of keratin, the same protein found in human fingernails and hair. The segments are loosely connected, allowing them to vibrate against each other without breaking apart.
The snake produces the sound by rapidly vibrating specialized muscles in its tail, known as “shaker” muscles. These muscles are among the fastest known in vertebrates, capable of contracting 50 to 100 times per second. This rapid movement causes the dry, hollow keratin segments to click and clack, generating a distinct buzzing sound. The hollow nature of the segments amplifies the sound, similar to how sound echoes in a cave.
How Rattles Form and Grow
A new rattle segment is added each time a rattlesnake sheds its skin, a process known as ecdysis. When a rattlesnake sheds, the modified scales at the tip of its tail do not detach completely but rather remain loosely attached, forming a new segment at the base of the rattle. Newborn rattlesnakes are born with a single “pre-button” or “button,” and they cannot produce the iconic sound until at least a second segment forms after their first shed.
The frequency of shedding, and therefore rattle growth, depends on factors such as the snake’s age, food availability, and environmental conditions. Younger snakes, which grow more rapidly, may shed several times a year, while older snakes might shed less frequently. Because segments can break off due to injury or daily activities in the wild, the number of rattle segments is not a reliable indicator of a rattlesnake’s age.