For Howler Monkeys, Louder Calls Mean Smaller…

For howler monkeys, it appears the louder the calls, the smaller the — ahem — balls. A research team looking into the monkeys’ incredibly loud and low vocalizations, and the physical structures that support the calls, discovered the correlation. Animals with louder and lower calls had larger hyoids, a bone in the front of the neck that appears to act as an amplifier, but smaller testes. There was significant variation in hyoid size between howler species, but also between male and females within a species. The disparity tipped researchers off that something else was going on.Loudest in the Room Howler monkeys produce one of the loudest vocalizations of any animal on the planet, and males use their voices to shout down competitors, attract mates and rope off their territory. But a closer look at the hyoids reveals an unexpected level of variation in between sizes. “If you thought of the ...