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Flanged vs. Unflanged Male Orangutans: A Rare Phenomenon in Nature

In orangutans, sexual dimorphism—the physical difference between males and females—is particularly striking. But even more intriguing is the two distinct forms of adult males: flanged and unflanged. Both forms are sexually mature and capable of fathering offspring, but they differ dramatically in appearance, behavior, and social strategy.

A multi genre photographer from India.
Pub: @BBC, @CNN, @NatGeo, @Greenpeace.
https://linktr.ee/AnilTPrabhakar


Unflanged Males

Appearance: These males look more like large adolescents—no cheek pads, smaller body size, and no throat sac.

Behavior: Unlike the dominant, vocal flanged males, unflanged males are more stealthy and avoid direct competition. They may not advertise their presence but can still be reproductively active.

Reproductive Strategy: Sometimes referred to as the “sneaky” strategy, unflanged males may attempt forced copulations, although in some cases, they may form temporary associations with females who tolerate them.

- Anil T Prabhakar

Flanged Males

Appearance: These males develop large cheek pads, or “flanges,” made of fatty tissue and supported by muscle, along with a prominent throat sac.

Behaviour: Flanged males are dominant and emit long, booming calls that can travel several kilometers. These calls serve to attract receptive females and to ward off rival males.

Social Role: They typically control large territories and are often the preferred mates of females, who seem to actively seek out flanged males for copulation.