Your work overall look aesthetic, or acceptable, but still there are some drawabox conceps that your ignored, so I'll try to cover them on the go:

Your organic forms overall look solid, but still there are some places where you didn't place the sausages properly; you weren't mindful that there were some matter below which affected the way in which the sausage was placed in your imaginary 3d space, like in this one: (, and which could be done better like this (or well, I would have done it like that): (

Of course you can do it better :), but my point is that you should be mindful of all the things you place, and how they relate to each other.

Also I'd like to encorage you to don't add sausages that wrap in a weird form. With this I mean that you place one on the top of the tower (for example) and make it fall to the floor (like one end is on the top and the toehr on the floor) since this can be hard to convey properly, and it may end up breaking the illusion. Instead try to wrap all the sausages in top of each other. You can use your contour lines as references to wrap the sausages; actually I'd say that that is one of their purposes.

Also there are some sausages whose forms strayed for the ones requested (check this: ( Distorting the sausages can break their solidity, so be careful with that.

Lastly, you could definitely push more the cast shadows. Their presence is minimum in your exercises.

Now, your constructions:

There's something that is extremely encouraged in drawabox: constructing additively. This means to base everything you add on what's already there. Starting simple and adding more things. Being mindful on the forms you add.

The construction is not to keep your proportions in track, nor to achieve a determinated form, is to onvey a 3d subject in its totality, always being congruent with what's already there.

This means that you should avoid cutting through your forms (though you can try, but is easier to add forms on the top) and to always add a 3d mass if you want to modify the a form.

There are demos in which uncomfortable doesn't add additional masses; where he simply add a line to modify the silhoette. Those demos are outdated, so the concept of construction is still there: that you should always add 3d things (

For example, in this page ( you clearly used an ellipse for the head, but you didn't mark the intersection between that head and the torso. Lining the intersections help to reinforce the solidity of the subject, since you are relating two different masses.

And on the other bird you cut its beak, which could mess up the illusion of 3d.

You also added modified their silhoette without a mass.

So, the way in which you could have done it with constrution is moe or less like this: ( With that I meant to base the extension of the silhoette with 3d masses.

That same principle applies for all of your drawings. You should be mindful of it.

The other issue I wanted to touch is about your legs.

In most of your drawings you used stretched balls for your legs. In this lesson however, the use of simple sausages for the legs in still encouraged. Notice how uncomfortable used simple sausages for the legs, and modified the silhoette with additional masses later: ( So try to always stick to sausage legs.

And well, don't use different pens to underline the construction. Limit yourself to add line weight to clarify.

Your texture overall its fine, tho limit yourself to break the silhoette. In the case of feathers, try to add them as cast shadows, and to push them out of the wing, not cut through it, like here: (

When you encounter a weird head, add attach masses to it. Sometimes a boxy form will do the job. SO overall try to draw the cranium and to extrude things out of it.

As for your question about opne jaws, well, I'd recommend to draw two boxy forms for each jaw, depending on how open is it: (

So you need to think on 3d while drawing. As I have already repeated many times: you need to add things based on what is already there.

Hope this is helpful!