What is the meaning of the underlined word courtesy as it is used in the passage ? 

The Sani are an indigenous people living in the northern parts of Norway, Sweden, Finland, and Russia's Kola Peninsula. Originally, the Sami religion was animistic; that is, for them, nature and natural objects had a conscious life, a spirit. Therefore, one was expected to move quietly in the wilderness and avoid making a disturbance out of courtesy to these spirits. Ghengis Khan is said to have declared that the Sami were one people he would never try to fight again. Because the Sami were not warriors and did not believe in war, they simply disappeared in times of conflict. They were known as "peaceful retreaters."