Saguaro Cactus

" Several types of desert birds drill holes into saguaros for nesting. The saguaro responds to the bird's damaging its tissue by secreting a resinous sap that, over time, hardens into a bark-like shell that prevents the cactus from losing fluid and also protects the nest hole by making it waterproof. The bird's nesting hole requires not only the bird's making a hole but also the cactus's lining the hole - it is not ready for use as a nest until a year after its creation."

I continue to be amazed at how plants and animals adapt for survival. The hole/future nest doesn't make a very impressive photo but the Geek in me just had to share. :)