Drawing the contour lines of an object is a technique I learned in life drawing, and I must say it is one of the BEST ways to learn how to draw.  Its only downside is that doing this is very time consuming, because truly studying a thing in depth takes a while.  When a person looks at anything your brain usually only sees the very most general features of the object because it takes very little for your mind to recognize and label the thing for what it is.  In this case, a person's brain would look at this picture and think "eagle", probably almost immediately.  An artist's eye has to be more exacting than that though to draw something and make it look truly realistic.  Artist's must look and see that "oh, the eagle's beak becomes more flat on the sides the further toward the eyes it gets, and the corners of it's mouth pucker out slightly, and it's eye is rather deepset and shaded by its eyebrow..."  None of these details are needed when simply looking at an object, but when you're the one putting line to page, you must be able to recognize all the little details of its form and articulate them properly.  I also did this technique on a horse's head.  Even though it takes a long time, it really is fun, and the end result is very worthwhile.

The particular reason I decided to do an eagle in this instance is that I really felt like I needed practice drawing eagle's heads and beaks.