It turns out that it seems that "the person whose voice is smaller is motivated"

Generally, it is thought that it is easier to leave descendants by appealing themselves strongly strongly in which living things,American BisonAs a result of studying the behavior of herds of herds, it seems that it was found that the female is weak against fight as much as the big barking male and is not mottained to the female.

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Shh! Quiet Bison Get More Sex | LiveScience

The study was conducted by Megan Wyman, a graduate student at the University of California Davis. Megan first tracked the herd for 2 months from July to August which is the estrus period of American bison, and collected the male chirp with a hand-held microphone, how many males the male mated, how many children I wrote about how the victory or defeat of female competition was born, and examined the correlation between the size of barks and the number of matings.

As a result, the male barking which had the largest number of matings was only two-thirds of the size of the smallest male, and he did not have any relation with the weight, age and the size of the bark. Perhaps the male seems to be conveying his strength not by the size of the voice but by the frequency and length of the squealing time, so it is unnecessary to make a big voice and a small voice is enough. Also, it seems that a small voice makes it less advantageous for other males to get in the way of mating, which is advantageous.

Conversely, I do not know well why a weak male imitates a strong male and does not make her voice smaller. For a weak male, it seems to be speculated that if the voice is small, it will come near to other male, so it may be because it is dangerous.