Origami Turkey Vulture

Turkey vulture is a type of vulture whose head and color just happened to look like wild turkey. I frequently see them in San Jose and its surrounding wilderness, slowly soaring and gliding on low altitude. Their V-shaped pose with occasional wobble is rather unique, so it is easy to identify them.

I wanted to design a simple local fauna, which can be taught in the future local convention (e.g EBOC). This turkey vulture is designed based on how they are usually seen: flying pose. I have to give it correct color change on the wings and tail feather. Its head is supposed to be red, but it's a shame that paper has only 2 sides and therefore, 2 colors. Just think of this as juvenile turkey vulture whose head is still brown.

Design

Let's begin with the features of turkey vulture in flight:

1. Broad wings with primary feathers on the tips. Those feathers will be represented simply with pleats, no need to use individual flaps like what I used for condor.
2. The underside of the wings is white in color, except the meaty top edge which I will refer as "colored arm".
3. The underside of the tail feather is white.
4. The bird's head, torso, legs, and the entire surface seen from top are dark brown.

The design started with great difficulty as I struggled to figure out how to put the colored body and arm under the white wings' side. I tried using fish, bird, or frog bases which had been very useful to bootstrap bird model, but none succeeded. Some wacky structures like asymmetric bases were even considered. Can't we just reuse the condor structure? Unfortunately not because the condor ignores color change and it can't be retrofitted to match this subject's color change.

In the end I resorted to imagine how the finished model would slowly got unfolded back to square, and come up with this basic half pig-base structure. The flaps on top will be used for the bird body, arm, and legs. The unused paper in the bottom can be opened with Elias stretch to change the pleat direction, and color changed. One side will be white, and the other side colored.

To move forward, the non-wings part requires more paper. The bottom part also requires paper to make tail. This is a straightforward scenario for blintzing.

Region inside highlighted line shows the original square

The structure looks slightly altered, but it is just a natural expansion with blintzing. I made them on actual paper, starting from blintzed base, then fold the half pig base, and open the bottom with Elias stretch. The excess part made from blintzing on top is filled with half bird base, which produces small flap for head and long flap for torso. Meanwhile the excess on the bottom is filled with rabbit ear. Somehow, someway, the small flap in the corner can be made to tail feather. We can figure it out later.

It was easy to improvise on how to form the primary feather pleats. We can do sink in and out on the edges to form parallel pleats. This structure have a lot of potential, and the design process gained a lot of momentum.

The next day, I feel like the wings are too short. We can elongate them by changing the square in the middle of blintz into rectangle. Let's use silver rectangle ratio that we all loved! Now the ratio of the inner squares changed from \(1 : 1\) to \(1 : \sqrt{2}\). This made the entire model be based on \(2 : 1 + \sqrt{2}\) ratio.

Regions highlighted with yellow rectangle have height to width ratio of  \(1 : \sqrt{2}\).
There is a slight modification on the wing pleats to retain more fully rectangular shape.

Why so complicated? Why can't we just fit everything in grid and use rectangle with ratio like 2 : 3? That's because using grid based reference for 22.5 model will end up with strange misalignment, and counter-intuitively more difficult reference finding. I'll move on with the silver rectangle ratio for now, and come back to this question.

Using silver rectangle would alter the top part which was used for the bird's body. With straightforward implementation, we would end up with stretched version of the structure from yesterday (see previous image). It has some unpleasant properties:

1. The small flap used for head is no longer pointy, but wide. Really w i d e. There is no straightforward way to make it pointy and resemble head anymore.
2. The edge flaps from the original half pig-base which were planned for legs are now splayed far apart. Again, no simple way to bring them together. 

Well, I suppose it's time to break away from what my friend Ivan called "bottom up" design, and instead use "top down". Which simply means, instead of staring at crease pattern and think hard to fill in the structure with the predefined common molecules, just try to design on actual paper with intuition. With that in mind, the top part is transformed into this half frog base thing. Any resemblance to the half pig-base is gone.

This structure eliminates the unpleasant properties, but there is still problem that it can't produce legs. Sure, there are many flaps to use, but none of them reached far down enough to qualify as legs. Should I add more paper with border or strip graft? Well... I don't really want to because when the whole bird body's part is unfolded, we can see that there are plenty of paper to utilize. There must be a way to fold legs out of it.

Plenty of paper is available in the front part

From the unfolded state, I refolded the body part while focusing on how to shift the paper down as far as possible, in a hope to create legs. It was purely free folded constrained with 22.5 degree. In the end, I found this working solution.

Step 1: converge the paper into center

Step 2: form head from the excess paper on middle-top, and squash all the way through the symmetry line.

Step 3: make the legs pointy with successive swivel folds.

The structure looks decent, I thought. So it's time to move to the tail. Like wings, the underside must be entirely white, and the top side is entirely colored. I experimented with squash and all those 22.5 maneuvers and ended up with 2 candidates. One is longer but uniformly narrow, while the other is shorter but wide. Actual turkey vulture will unfurl its tail feather to provide extra lift at the cost of increased drag, and fold it back for the other way around. So both variants can be used. I made both as test folds, and I prefer the shorter but wide one.

Possible tail structures. based on my condor's head (left) and halibut tail (right).

I made bunch of test folds to figure out proper way to spread the pleats on primary feather. While doing so, I found a way to make the bird body more interesting. First, sink the tiny bird base flap, then slowly pull apart the bird body at the sunk region. Finally, make wedged crimp in the bottom to represent thighs. This makes the bird's body 3D and nicer transition to its legs.

The whole model is still simple, but unfortunately requires difficult maneuver, especially on the wing pleats formation. When taught, this can easily take 2 hours. So I am not sure if this is teachable in local convention.

Let's get back on the topic of using grid based reference. This is how the final crease pattern would look like if rectangle with 3 : 2 ratio is used instead of silver ratio. It works, yes. However there are parts that don't fully form flaps, as circled on the picture. The folded form also has some edges that don't meet at common points.

Circled region shows misalignment

Fold

For simple model like this, I prefer to use common origami paper (kami). However I don't have suitable color. The final fold ended up using brown tissue + white machine made speckled unryu. This particular unryu I bought from Blick looks fancy, but its quality isn't too good. There aren't many "squiggly coarse fiber" that defines unryu and it wasn't as durable as handmade unryu.

Obligatory initial square paper

Speckles on the unryu, and strangely no squiggly coarse fiber is visible

The pig base starting point

Elias stretched to produce main color change for the wings

Wing pleats added

Drying inside this tubular container to hold the wings position in V-like pose

I made 2 final folds so the picture can simultaneously show both top and under side.

Why Wobbly Flight?

Having seen them in flight, I wonder why would they wobble side to side during flight? Other birds seemed to fly stably. Are they suck at flying? Apparently it's quite the opposite.

Turkey vultures rely on smell to find dead body. This means they need to fly in lower altitude to pick up the smell. Lower altitude soaring is challenging because there are not much updraft or wind, so they have to make use of every little air disturbance to subsidize their flight, including tiny updraft or wind turbulence produced by wind colliding with trees. With their V-shaped pose, wobbling would control which wing gets to catch those tiny air differences and in turn, produces lift. In short, their wobbling is a fine tuned positioning to use every resource in the air to minimize energy expenditure.

Anyway I am by no means an expert in this field, let alone proper English writer. If you would like to learn more, check this publication https://academic.oup.com/auk/article/133/1/79/5149077.