Why might some mammals pull their testes back into their body in the non-breeding season?

Some mammals retract their testes into their body during the non-breeding season to regulate temperature and protect them from environmental stressors. The testes need to be kept cooler than the body temperature for optimal sperm production; pulling them closer to the body can help maintain warmth during colder months. Additionally, this behavior may serve to protect the testes from injury or predation when they are not needed for reproduction.