隹 centers on a bird, specifically a short-tailed bird in its historical radical sense. It is not commonly used as a standalone character in modern Japanese, but its meaning is simply 'bird'.
隹 is a pictograph of a short-tailed bird. The modern form retains a stylized bird shape with a head, body, and wing-like strokes.
Meaning mnemonic
The top-left strokes suggest a bird's head and beak, while the lower right strokes form the body and short tail. Picture a compact bird perched on a branch.
Reading mnemonic
For サイ, imagine a bird sighing (サイ) as it perches: sigh -> サイ, and the bird lets out a soft sigh.
