Combinators

A combinator is a function or operator that only refers to its arguments and operands without modifying them in any way.

Symbol	APL expression	Bird⁽¹⁾	TinyAPL	Diagram
$\mathrm I$	`y`	Identity	`⊣`/`⊢`
$\mathrm K$	`x`	Kestrel	`⊣`
$\kappa$	`y`	Kite	`⊢`
$\mathrm W$	`y F y`	Warbler	`⍨`
$\mathrm C$	`y F x`	Cardinal	`⍨`
$\mathrm B$	`F (G y)`	Bluebird	`∘`/`⍤`/`⍥`
$\mathrm Q$	`G (F y)`	Queer	`⍛`
${\mathrm B}_1$	`F (x G y)`	Blackbird	`⍤`
$\Psi$	`(G x) F (G y)`	Psi	`⍥`
$\mathrm S$	`y F (G y)`	Starling	`⟜`/`⇽`
$\Sigma$	`(F y) G y`	Violet Starling	`⊸`/`⇾`
$\mathrm D$	`x F (G y)`	Dove	`∘`/`⟜`
$\Delta$	`(F x) G y`	Zebra Dove	`⍛`/`⊸`
$\Phi$	`(F y) G (H y)`	Phoenix	`«»`
$\Phi_1$	`(x F y) G (x H y)`	Pheasant	`«»`
${\mathrm D}_2$	`(F x) G (H y)`	Dovekie	`⊸` + `⟜`
$\mathrm P$	`(y G x) F (x G y)`	Parrot⁽²⁾	`⸚`
$\mathrm N$	`x F (x G y)`	Eastern Nicator	`⇽`
$\mathrm \nu$	`(x F y) G y`	Western Nicator	`⇾`

Additionally, some other primitives have combinator-like behavior:

APL expression	TinyAPL	Diagram
`n`	`⍨`
`n`	`⍨`
`F y`	`⁖`
`x G y`	`⁖`

Some combinators have bird names, originating from To Mock a Mockingbird by Raymond Smullyan. Some of the bird names are taken from the Uiua combinator page.
I made this one up.