I too vote for misplaced hunting. Our four year old fixed male does the same thing, except he confines it to his cloth covered slinky toys shich are his favorites. He brings them and drops them somewhere near us, then goes to sleep. Occasionally he howls until we come to see them, sometimes they just get dropped on the bed near us. Personally, I much prefer stuffed toys to dead mice
, so I'm not discouraging him.