They were play fighting with each other and yipping and barking.

他们互相打斗，又叫又叫。

I go skiing and I play snowball fights and I build snowmen.

我去滑雪，打雪仗，堆雪人。

With no food or females to compete over, these play fights are harmless, but the contests mean each bear can gage the strength of its opponents.

由于没有食物或配偶可争，这种游戏般的打斗毫无伤害，但这样的比赛却可以使每头公熊估量出对手的实力。

And it is also acting in the brain to motivate later behaviors, like play fighting, that are particularly beneficial to many male mammals.

而且它还能在大脑中发挥作用， 激发诸如打闹之类的后续行为，这对许多雄性哺乳动物特别有益。