Hi this is my instructables on a penguin
Choose a pose. Draw the outline of the main ways the body. I prefer to start with the head and spine, then attach the fusiform body. At this point, you should already have a selection of photos as reference for your illustration
Add limbs and tail. You must have clear the perspective in your drawing, in this case the difficulty is that you're drawing paired structures, but the perspective and poise makes them asymmetric, it is important to know the correct position that must have the extremities in relation to the body position.
Define the silhouette. Give some touches of realism, such as small feathers below the peak and in the lower boby. Establish general characteristics of the face. Which it is simple, because the birds do not have facial muscles to give them expression.
Anatomy. This is what I am interested that you understand. If you want to learn to draw a realistic animal, you should study anatomy! The correct position of the bones determined the basis for body volume, the correct location of the limbs, etc. You should understand what you are drawing! So, if you want to draw a realistic penguin , please do not stay just with this basic tutorial and go to find pictures on the internet or in books and STUDY them! Now if you go to a zoo to see live animals .. even better!
Here you can see the relation of the skeleton with the body volume and position.
Features. Add color patterns that define the specie.
In this case, the animal is a Humboldt penguin. You can see that in his neck has one black collar, unlike the Magellanic penguin (with which could be mistaken) that has two black lines. Cape penguin has facial features that can differentiate from the Humboldt penguin.
I hope that this tutorial has been helpful ;)