Where does the word "thlypis"/θλυπις come from?

Question

A number of New World warblers seem to have genus names that end in the element -thlypis. It's been hard for me to find information about the etymology of this element; I found a few sources on the web that say that it comes from a Greek word θλυπις that referred to some kind of bird, but I can't find any detailed description of this word, only brief mentions of it. The Wikipedia article on the "Common yellowthroat" says

The genus name Geothlypis is from Ancient Greek geo, "ground", and thlupis, an unidentified small bird; thlypis is often used in the scientific names of New World warblers.

The Helm Dictionary of Scientific Bird Names, by James A. Jobling, seems to corroborate this statement:

Euthlypis Gr eu fine, good; thlupis unknown small bird, perhaps some sort of finch or warbler. In ornithology thlypis signifies either a parulid warbler or a thin-billed tanager.

I'd like to know where exactly θλυπις occurs in Greek texts, and whether we know anything more about the word than its spelling and the vague idea of its meaning that is described in these quotations. For example, do we know how it is declined, or the length of either of the vowels? I couldn't find this word in any online dictionaries of Greek.

Answer 1

According to LSJ, θλυπίς is a variation of θραυπίς, which occurred in Aristotle's Historia Animalium, Book viii, ch. 3:

Ταῦτα μὲν οὖν καὶ τὰ τοιαῦτα τὰ μὲν ὅλως, τὰ δ´ ὡς ἐπὶ τὸ πολὺ σκωληκοφάγα, τὰ δὲ τοιάδε ἀκανθοφάγα, ἀκανθίς, θραυπίς, ἔτι ἡ καλουμένη χρυσομῆτρις. Ταῦτα γὰρ πάντα ἐπὶ τῶν ἀκανθῶν νέμεται, σκωλήκα δ´ οὐδὲν οὐδ´ ἔμψυχον οὐδέν· ἐν ταὐτῷ δὲ καθεύδει καὶ νέμεται ταῦτα.

Translation:

The above-enumerated birds and the like of them feed either wholly or for the most part on grubs, but the following and the like feed on thistles; to wit, the linnet, the thraupis, and the goldfinch. All these birds feed on thistles, but never on grubs or any living thing whatever; they live and roost also on the plants from which they derive their food.

Other than that, θλυπίς and θραυπίς appear in a number of reference works, such as Griechisch-Deutsches Wörterbuch:

θραυπὶς, ἡ, ein Vogel wie der Distelfink, carduelis; auch θλυπὶς, θλιπὶς, γράπις, geschrieben

Martini Rulandi Medici Synonyma:

Carduelis - Θραπὶς. θραυπὶς. ποικιλῖς. Ἀκανθὶς

A New and Complete Greek Gradus:

Ακανθις, ίδος. ἡ. carduelis. goldfinch, or linnet, αειδον κορυδοι και ακανθίδες, εστενε τρυγών. Theoc. 7. 141. SYN. Θραυπις, ποικιλις.

Nichtlateinische Schriftzeichen:

Κάρδερίνα, π. - Ποικιλὶς, θραυπὶς (ἴδε Φλυτζοῦνι εἰς τὸ Παράρτ.), ἀκανθῖς καὶ ἀκανθυλλὶς (ἠ ποιλίκη), ἀστραγαλῖνος, χρυσομῖτρης. chardonneret.

Answer 2

Just to expand on Expedito Bipes's answer (and Alex B.'s and fdb's comments) and clarify a bit:

The word θλυπίς (thlypis) is a hapax legomenon ("thing said only once"), that is, a word found only once in the whole canon of Ancient Greek literature. In particular, it's found in a particular manuscript of Aristotle's Historia Animalium (VIII.3).

Most manuscripts have the passage the way Expedito quotes it: namely with the word θραυπίς (thraupis). It's unclear whether θλυπίς is a typo, or whether it's another word for the same type of bird (so a synonym). Judging from Expedito's sources, many lexicographers take the second option, and that's how it ended up in scientific names for birds.