The phrase "human intruders" refers to people who enter a place or situation where they are not welcome or should not be. They are like unwelcome guests. Full definition
The DAS app sends alerts when a potential problem arises — if an elephant bolts, for example, or if field sensors pick up on human intruders. (scientificamerican.com)
Because the Alaskan Malamute was developed in the Alaskan wilderness, and all members of the human group were part of the dominant pack, and all of their belongings were shared between them and unexpected strangers were welcomed with hospitality - there was no need for the Mals in the community, to guard the humans» belongings against human intruders. (animals-universe.info)