Dogs poop in alignment with Earth’s magnetic field, study finds (2014)
I have four dogs, and I watch them poop every day.  For some reason they have to slowly turn lots of circles before they're satisfied they have the best pooping position, and if the sun is out, they almost always settle on a position where they're not facing directly into the sun.Makes sense from a practical viewpoint.  You're more vulnerable to attack when you're pooping out in the open, and even moreso if the sun is right in your eyes.To the extent that more pooping is done near the middle of the day, north-south pooping orientation would naturally dominate.  No need for a sixth "compass" sense.