Did you know the loudest land animal is the howler monkey? Trish and I have been lucky enough to see and hear howler monkeys in Belize and in Costa Rica. You can literally hear them several miles away as they call to each other.
Howlers often howl at each other in territory disputes. However, the males also use their raucous howls to attract mates. Perhaps you already know that, but I'm going to tell you a part of the story you may not know... the loudest male howler monkeys have the smallest testicles. Yep, that's right. Louder calls = smaller balls.
Studies have revealed that howler monkeys basically have two different types of social structures: 1. Single-male groups in which one male has a harem of a few females. 2. Larger, multi-male groups in which multiple males mate with multiple females.
The males in single-male groups have louder calls, yet they have smaller testicles (which produce fewer sperm cells). The males in larger, multi-male groups have softer calls, yet they have larger testicles (more sperm produced).
Why? Because males with louder voices are better able to convince females to join their harem... but, on a day-to-day basis they are not competing with other males to produce offspring with those females. Therefore they do not need excessively high sperm production.
And males with softer voices are not able to form their own harems, and they must compete with other males to produce offspring with the same group of females, therefore they benefit by having larger testicles that produce more sperm cells.
Aren't you glad you asked?
- Howler Monkey - DepositPhotos
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