{"id":286808,"date":"2026-01-16T02:28:15","date_gmt":"2026-01-16T02:28:15","guid":{"rendered":"https:\/\/www.europesays.com\/ie\/286808\/"},"modified":"2026-01-16T02:28:15","modified_gmt":"2026-01-16T02:28:15","slug":"monkeys-with-smaller-testicles-scream-louder-to-compensate","status":"publish","type":"post","link":"https:\/\/www.europesays.com\/ie\/286808\/","title":{"rendered":"Monkeys With Smaller Testicles Scream Louder to Compensate"},"content":{"rendered":"

\"\" <\/a>Howler monkey in Santa Maria de Jetiba, Brazil. Photo by Paulo Chaves.<\/p>\n

It\u2019s a long-held belief that loudmouths overcompensate for something, but in the case of howler monkeys, science has confirmed it\u2019s a biological fact. A landmark study by Dr. Jacob Dunn at Cambridge University, along with 2026 follow-up research<\/a>, has established that monkeys who scream the loudest effectively \u201cpay\u201d for that volume with significantly smaller testes and lower sperm counts.<\/p>\n

Howler monkeys are one of the few nest-building monkeys, and one of the loudest creatures in the animal kingdom. They generally live in groups of 6-12 individuals, with only a few males and many more females, in a harem style of arrangement.\u00a0Biological anthropologist Jacob Dunn and his team from Cambridge University wanted to see how the size of the monkey testicles plays into social arrangements, and how they correlate with their screams.<\/p>\n

Specifically, the team calculated how loud monkeys scream depending on the size of their testicles.<\/p>\n

\n

\u201cThe results of our acoustic analyses show that howler monkeys produce roars at a similar frequency as tigers, which is far lower than we would have predicted from their body size, yet exactly what would be predicted from measuring their giant vocal folds\u2019 which are three times bigger than in a human.\u201d<\/p>\n<\/blockquote>\n

Dunn\u2019s team analyzed the biological \u201cbudget\u201d of these primates and found a direct negative correlation: males with large hyoid bones (the hollow throat bone that acts as an echo chamber) produce deeper, louder roars but have smaller testes. Males with smaller hyoids have quieter calls but significantly larger testes.<\/p>\n

This trade-off dictates their social lives. Males with \u201cloud mouths and small testes\u201d are typically the ones who live in harems (one or few males, many females). They use their terrifying roar to keep rival males away, meaning they don\u2019t need to compete via sperm count. Conversely, males in large, mixed groups rely on \u201csperm competition\u201d mate with the same females as other males so they invest their energy in testicular size rather than vocal volume.<\/p>\n

Howling Like a Tiger<\/p>\n

\"Vocalizing <\/a>Credit: Pexels.<\/p>\n

Why is the roar so expensive to produce? It turns out the monkeys are engaging in \u201cacoustic deception.\u201d A recent study revealed<\/a> that the enlarged hyoid bone lowers the sound\u2019s frequency, allowing an 8kg (17 lb) monkey to sound like a tiger. This phenomenon, known as \u201chonest exaggeration,\u201d tricks rivals into thinking the caller is physically massive, preventing dangerous physical fights.<\/p>\n

\n

They do this through a unique adaptation of a vocal membrane<\/a>. This is a tiny ribbon of tissue above the vocal cords; we humans have lost this membrane.<\/p>\n

This membrane creates chaotic, non-linear sounds (similar to a death metal scream or an erratic yodel), which are biologically designed to be impossible to ignore.<\/p>\n

\u201cIt may be that investment in developing a large vocal organ and roaring is so costly that there is simply not enough energy left to invest in testes,\u201d Dunn explains<\/a>. \u201cAlternatively, using a large vocal organ for roaring may be so effective at deterring rival males that there is no need to invest in large testes.\u201d<\/p>\n

To a lesser extent, this may be a broader adaptation among primates. As one 2019 study noted<\/a>, \u201cacross this primate genus, those species that invest most in the development of the hyoid and larynx [..] have the smallest testes [20].<\/p>\n<\/blockquote>\n

In the end, at least for the howler monkeys, it works: the loudest males may have the smallest \u201cequipment,\u201d but they successfully gather the largest harems.<\/p>\n

Journal Reference<\/a>:\u00a0Evolutionary Trade-Off between Vocal Tract and Testes Dimensions in Howler Monkeys.<\/p>\n

\u00d7<\/p>\n

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This article was originally published in 2016 and has been updated with additional information.<\/p>\n","protected":false},"excerpt":{"rendered":"Howler monkey in Santa Maria de Jetiba, Brazil. Photo by Paulo Chaves. It\u2019s a long-held belief that loudmouths…\n","protected":false},"author":2,"featured_media":286809,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[273],"tags":[18,143698,19,17,133,143699,461],"class_list":{"0":"post-286808","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-wildlife","8":"tag-eire","9":"tag-howler-monkey","10":"tag-ie","11":"tag-ireland","12":"tag-science","13":"tag-testicle","14":"tag-wildlife"},"share_on_mastodon":{"url":"https:\/\/pubeurope.com\/@ie\/115902421531308563","error":""},"_links":{"self":[{"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/posts\/286808","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/comments?post=286808"}],"version-history":[{"count":0,"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/posts\/286808\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/media\/286809"}],"wp:attachment":[{"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/media?parent=286808"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/categories?post=286808"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/tags?post=286808"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}