The webpage adds some unnecessary confusion by

1) using colored shapes instead of variable names.

2) (initially) presenting combinators as having 3 arguments, where they only need 1 or 2. So instead of the usual M x = x x, you see M x y z = x x y z.

One (improper) bird I find very interesting is the Starling's cousin S* x y z = x z (y (K z)), from which all other birds can be reconstructed.