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Quirks and Quarks

Howler Monkeys: Big Calls Mean Small Balls

The deep , carrying call of the male howler monkey is used to attract mates, though the loudest monkeys turn out to have traded volume of call for volume of sperm production.

The loudest monkeys have the least to howl about.

CBC News ·
A chorus of howler monkeys of the species Alouatta caraya. (Mariana Raño)
Quirks and Quarks10:28Howler Monkeys: Big Calls Mean Small Balls - 2015/10/24 - Pt. 1
Howler monkeys are found in the forests of South and Central America.  They are so-named because they make one of the loudest calls of any land animal. Their deep howl - particularly that of the male - will intimidate rivals while attracting the attention of a female.

But a new study by Dr. Leslie Knapp, a Professor and Chair of the Department of Anthropology at the University of Utah, has found that in the howler monkey, there is an evolutionary trade-off between vocal characteristics and sperm production.

Male howler monkeys with large hyoids - the bone adapted to resonate sound - have smaller testes than males with small hyoid bones.Those with large hyoids tended to be the only male in their group, which suggests high levels of vocal competition. Those with larger testes tended to live in a group with several males, which indicates strong sperm competition. The connection between the roar of the howler money and reproduction was first suggested by Charles Darwin, but not tested until recently.  

Related Links

- Paper in Current Biology
- University of Utah release
- University of Cambridge release
- Live Science story
- Science magazine news story

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