Howler Monkey

Howler monkeys. From their Central and South American rainforest home, they produce some of the loudest animal calls in the world. They're about the size of an [adult:mature] cocker spaniel, but they can sound as large as a tiger.Biologists have long [suspected:regulated] that the monkeys' howls played a role in attracting mates. The sounds are like the [auditory:auditive] version of peacock feathers or deer antlers that say, hey, check me out.And now we know that the [quality:standard] of the howl depends on a bone near their throats called the hyoid. The bigger the hyoid, the deeper the howl. [Males:Man] with deeper calls sound more attractive to females. Which means that males with smaller hyoids had to come up with another strategy."When you're in the field and you look up at the monkeys, you notice that in Alouatta palliata, the mantled howler monkey, that the testes are huge. And they're [white:black] , they're really obvious."University of Utah anthropologist Leslie Knapp. She and her team found that howler monkeys face an anatomical trade-off: a species can either have a really [big:huge] hyoid bone, or it can be very well endowed.