I'm always intrigued by cholla cactus and every time I see one, I bend over to see if there is a birds nest in it. Yup. this one, even though it was ony 3 feet high, had a bird's nest! The spines of the cholla prevent predators from invading the nest. And, LOOK at those spines! OUCH! Cactus Monday for January 10, 2011.