This would be a good opportunity to do a soil sample and see if there is a correlation to what you're observing. I believe animals can tell the difference in plots that are more nutritious. Science tells us that plots with the proper pH are better able to utilize the nutrients in the soil and should be more nutritious.

If soil tests on these plots don't reveal a correlation then your answer lies elsewhere. Maybe the plots being used heavily are closer to prime bedding areas. Either way, you've got some pieces to an interesting puzzle. If you piece it together, it could pay off in the future.