Bird base · verified flat-foldable
The Common Ancestor
This family is not rigid-foldable — the paper has to bend on the way, so there is no continuous 3D motion to show. Step diagrams are the honest way, and the way every origami book does it.
Open the diagram sheet →How to fold it
- Fold the square in half vertically
- Fold the folded shape in half horizontally — the front base is ready
- Bring the horizontal raw edge to the center line and unfold (bottom-left)
- Bring the vertical raw edge to the center line and unfold (bottom-left)
- Lower the top triangle and unfold — petal hinge (bottom-left)
- Bring the horizontal raw edge to the center line and unfold (bottom-right)
- Bring the vertical raw edge to the center line and unfold (bottom-right)
- Lower the top triangle and unfold — petal hinge (bottom-right)
- Bring the horizontal raw edge to the center line and unfold (top-right)
- Bring the vertical raw edge to the center line and unfold (top-right)
- Lower the top triangle and unfold — petal hinge (top-right)
- Bring the horizontal raw edge to the center line and unfold (top-left)
- Bring the vertical raw edge to the center line and unfold (top-left)
- Lower the top triangle and unfold — petal hinge (top-left)
- Make the petal fold: lift the bottom point up, letting the side edges come in on their own, then turn the paper over and repeat on the back — the bird base is complete
Pre-creasing every line before you collapse is the whole trick. Paper remembers.
The story below, read word for word by a synthetic voice over this fold's own music.
Someone taught you this fold, or someone taught the person who taught you. That is nearly always how it goes. A grandmother at a kitchen table, a teacher with a stack of coloured squares, a stranger on a train who folded a napkin into a bird and left it behind when she got off. The hands remember it before the mind does.
The Common Ancestor, catalogued here as FSA-0001, is not our design. It is traditional. No name is attached to it, and none should be invented. What belongs to Foldsong is this page: the measurements, the story, the music, the recording. The fold itself belongs to everyone who has ever made it.
Why there is no animation on this page
The bird base sits at the root of a large family. From it you can reach the crane, the flapping bird, and a long list of variations that share its skeleton. That shared skeleton is why we call it an ancestor rather than a model.
It is also a fold that will not behave for a computer. The bird base is flat-foldable — the paper lies down without tearing, and the classical conditions describe why. Kawasaki's condition governs how the angles around a vertex must alternate. Maekawa's counting rule governs the difference between mountain and valley creases meeting there. Both hold at every interior vertex in this pattern.
Rigid foldability is another matter. This family is not rigidly foldable: to get from flat sheet to finished base, the paper must bend along the way, curving in regions that no ideal panel model allows. Simulate it as stiff plates hinged at the creases and the motion locks. That is not a failure of the fold; it is a fact about it. Because the motion cannot be reduced to hinged panels, we did not measure a rise height or a folding range, and we will not print numbers we did not measure. You get step diagrams in Yoshizawa–Randlett notation instead, which is what the fold has always used.
The pattern, counted
The crease pattern has 13 corners and 32 creases. Of those creases, 11 are mountains, 13 are valleys, and 8 sit on the boundary of the square. Five interior vertices carry the whole structure, and flat-foldability was confirmed at all 5.
The angles are austere: 45°, 67.5°, 90°. Nothing else. The ratio check across the pattern runs from 45.0° to 90.0°, a narrow band with no thin slivers and no near-degenerate wedges. This is part of why the fold is teachable. Thin angles punish imprecise hands; these do not. A beginner folding slightly off-centre still gets a bird base, just a slightly crooked one.
The character of it is patience. The petal folds ask you to commit — you lift, you flatten, and for a moment the paper resists and then gives. Both crease families bend during that moment. The form rises anyway.
Someone will learn it from you, and will not ask who made it.