Beyond a shadow of a doubt, quail will set in prickly pear and allow dogs and hunters to move within a few feet without flushing. Many times a dog will never smell them. I believe there is some sort of masking of scent that takes place in prickly pear.
Numerous times we have had quail scattered in an area covered with prickly pear. Dogs and hunters would have moved through, often more than one time, and I would happen to look down into prickly pear and see a bird setting. It would take throwing several rocks in that prickly pear to get that bird to budge. Here’s another example that has happened more than once in prickly pear: a dog will be on point, staring straight at a bird in the prickly pear patch. We’ve thrown rocks into the patch – no flushing it out this time. I’ve had to find a stick long enough to reach into the prickly pear patch and poke the bird in the tail to finally flush it. It didn’t take many times of seeing this behavior to know beyond a shadow of a doubt that many quail have just set tight in a prickly pear watching us pass by.