The bird table has evolved because of the need to know - quickly - where the binoculars and the bird reference books are.
Just this morning, for instance, there was a small group of wading birds fossicking ahead of a turning tide, that looked a bit like oystercatchers but they seemed to be mostly black instead of the black and white 'pied' oystercatcher that we know and love. And if the truth be known, they were just a little portlier than your average oystercatcher, and they were certainly way too chunky to be the rarely seen black stilt.
Thanks to the field guides, we were able to satisfy ourselves that these were probably the "variable oystercatcher" in its "black phase".
These delightful creatures have several different outfits, just to keep the newby bird watchers on our toes!