Jamieson, Fausset and Brown on Jeremiah 12:9

9. speckled bird--Many translate, "a ravenous beast, the hyena"; the corresponding Arabic word means hyena; so the Septuagint. But the Hebrew always elsewhere means "a bird of prey." The Hebrew for "speckled" is from a root "to color"; answering to the Jewish blending together with paganism the altogether diverse Mosaic ritual. The neighboring nations, birds of prey like herself (for she had sinfully assimilated herself to them), were ready to pounce upon her.

assemble ... beasts of ... field--The Chaldeans are told to gather the surrounding heathen peoples as allies against Judah (Is 56:9; Eze 34:5).