TT #132 · Parshas Shemini · Aliyah 6 · Passuk 13
Chabad.org — Vayikra Chapter 11 with Rashi
English: These you shall abominate among the birds; they shall not be eaten—they are an abomination: the eagle, the bearded vulture, the black vulture.
Chullin 61a.
E-Daf.com — Chullin 61a (Tsurras Hadaf)
אֶת הַנֶּשֶׁר. תַּנְיָא, וְאֶת אֵלֶּה תְּשַׁקְּצוּ מִן הָעוֹף אֶת הַנֶּשֶׁר, מַה נֶּשֶׁר מְיֻחָד שֶׁאֵין לוֹ אֶצְבַּע יְתֵרָה וְזֶפֶק וְאֵין קֻרְקְבָנוֹ נִקְלָף וְדוֹרֵס וְאוֹכֵל.
Definition by characteristics — The eagle is identified through its distinctive physical characteristics, which distinguish it from other birds.
The Gemara identifies the characteristic signs associated with the forbidden birds, including the vulture's signs and predatory behavior.