What can you learn from observing and comparing specific physical traits of different birds?

There are so many different types that come to eat and as I watch them I notice that some of the finches look very much alike but are different breeds. You can look at the shape of a bird's body, wingspan, colors especially and markings and determine the type of bird, if it is native to your area or visiting, if it is male or female. I have a bird book I like to use, it's called, wild birds of north America. It has tons of color photos and info. If you want to draw lots of interesting birds, try a thistle feeder instead of mixed wild bird seed. This will draw in the finches and other colorful small birds that you don't see flying around that often.