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Eland Bull

Elands Use Non-Aggressive Signals to Establish Dominance

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Eland Bull

An eland (Tragelaphus oryx) bull.

Photo © Jakob Bro-Jørgensen / Cambridge University.

Eland antelopes (Tragelaphus oryx) are the largest antelopes in the world but their considerable size doesn't mean they're eager to throw their weight around. It turns out, eland antelopes have developed elaborate means to avoid fights and in doing so, they avoid costly injury associated with physical conflict.

When settling disputes, male elands send out a set of signals that accurately reflect their size, age, and aggressiveness to other males—these signals serve to advertise the fighting ability of each male. If it is clear one individual would likely overpower an opponent, the weaker individual simply acquiesces, sparing both individuals any injury.

This complex communication process between rivals—referred to as agonistic signaling—is the focus of research reported earlier this month in the journal BMC Biology. The study's authors include Jakob Bro-Jørgensen from the Zoological Society of London and Torben Dabelsteen from the University of Copenhagen.

Bro-Jørgensen and Dabelsteen recorded data for eland antelopes in Kenya's Masai Mara National Reserve and the Olare Orok Convservancy. The study area stretched over 400 square kilometers of acacia savannas and open grasslands.

Based on their observations, Bro-Jørgensen and Dabelsteen identified three agonistic signals that rival male elands use to communicate dominance to each other:

  • delap size
  • knee clicks
  • hair darkness

Each signal conveys a different type of information. Dewlap size provides a measure of the animal's age—older males have larger dewlaps than younger individuals. Since older elands are likely to have more fighting experience, a larger dewlap gives some indication of which individual is more likely to prevail in a fight.

Knee clicks provide a measure of the animal's size. Knee clicks are thought to be produced by a tendon slipping over the knee joint (much like sound made when plucking a taught string). Knee clicks are loud enough to be heard several hundred meters away. In larger antelopes, the sound produced is lower frequency than in smaller antelopes, so the deeper the sound, the larger the animal.

Finally, hair darkness provides a measure of relative aggressiveness. Darker hair, which results from higher levels of androgens, indicates a more aggressive individual.

Find out more: Bro-Jørgensen J. and T. Dabelsteen. 2008. Knee-clicks and Visual Traits Indicate Fighting Ability in Eland Antelopes. BMC Biology. November 5, 2008.

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