sorry if this has already been asked before, but i cant find it anywhere. so, if i start exploring with one pet, then switch my active pet and then enter an island with that pet, will my first pet be kicked out of the island? what will happen to it if anything? i'd really like to know, because one of my pets is stuck deep in the tundra and i really dont want to move him... but my other pets need to explore too!

The first pet will stay on the island it was exploring, and you can go back to it whenever you want. I've often left multiple pets on the tundra at once to let them recover their energy without losing the level they're on, and explored with other pets in the meanwhile.  

nice! thank you!