Things That Go Bump

Things That Go Bump

Credit: PLoS ONE

While diving off Wake Atoll in the North Pacific, researchers discovered a bizarre head-butting behavior in the bumphead parrotfish that live there. The violent collisions occurred at spawning grounds. Shown here, a partial spawning aggregation of of the bumphead parrotfish consisting of 246 individuals.

Who's In Charge?

Who's In Charge?

Credit: PLoS ONE

The second head-butt, shown here, between two male bumphead parrotfish. The butting makes such a loud sound that at first the researchers thought it sounded like a spear gun.

You Win

You Win

Credit: PLoS ONE

Here, following the fourth charge, the subordinate male (right) capitulates, rapidly fleeing the area with use of the caudal fin.

Bumpy Head

Bumpy Head

Credit: PLoS ONE

The dominant male, showing scale damage on back and side, is shown here following the head-butting bout. The giant bumphead parrotfish (Bolbometopon muricatum), which can reach 4 feet (1.3 meters) long and 100 pounds (46 kg), is named for its bulbous foreheads (shown here); its eccentric look gets a boost from the pouty lips and yellowish-to-pink face.

Different Foreheads

Different Foreheads

Credit: PLoS ONE

A female Bolbometopon (lower fish) and male (upper), illustrating the differences between the sexes in forehead and size; the female's forehead slopes caudal to the beak, but is nearly parallel with the beak in males. Males are also typically larger than females.

Sexual Selection

Sexual Selection

Credit: PLoS ONE

Here, a closer look at the male parrotfish's ossified bump atop its head. The researchers suspect sexual selection played a role in the development of the bump and the head-butting behavior it allows.

Wake Atoll

Wake Atoll

Credit: PLoS ONE

The researchers conducted surveys on a biennial basis by the NOAA Coral Reef Ecosystem Division. Circles indicate the total number of fish observed at each location around Wake Atoll in the North Pacific Ocean.