As you mention, Latin hippopotamus, -i comes from Greek ἱπποπόταμος, which is a compound of ἵππος (hippos = horse) and ποταμός (potamos = river).
In Latin, Lewis and Short cites instances in Pomponius Mela (AD 45), Pliny (AD 79), and Ammianus Marcellinus (AD 400). In Greek, the LSJ includes references from Dioscorides (AD 90), Galen (AD c. 200), and ...
If you want to say "night bird" with the words "night" (nox) and "bird" (avis), you should say "bird of the night", avis noctis.
When you decline this expression, noctis (of the night) remains in the genitive case whereas avis takes the required case.
A more Latin way would be to use an adjective.
I would go with nocturnus (nightly, nocturnal or nighttime).
Unfortunately, the verbs have survived much better in writing than the actual onomatopoeia. A few of these are fairly clearly based on the sound: baubor "bark", hinnio "whinny", ululo "howl" (and ulula "owl"), mugio "moo", crocio "croak". See Suetonius, De Naturis Animantium for a long list of these.
As far as directly transcribing animal sounds, only a few ...
The word dragon is far older than the Medieval dragon or the West's knowledge of the Chinese dragon. In fact, it's no coincidence, either, was dragon is derived from draco. It's the meaning of the former which has changed, so as an archaicism, dragon is still a fine translation.
As to what the Greeks and Romans thought of draco (and δράκων), these would be ...
Animal is certainly applicable to men, both in classical literary usage and in prevalent philosophical discourse.
Classical Literary Usage
Referring to man
First, a few examples of animal being used to refer to men, all taken from the Lewis & Short entry for animal:
animal hoc prouidum, sagax, multiplex, acutum, memor, plenum rationis et consilii, ...
The Online Etymological Dictionary states
His [Castor's] name was given to secretions of the animal (Latin castoreum), used medicinally in ancient times. (Through this association his name replaced the native Latin word for "beaver," which was fiber.)
Castoreum has been used medicinally since Classical times, prominently as an ingredient in material ...
Indeed, I cannot find any hits for "purr" in the LSJ, nor any verbs containing the words "cat" or "cats" in their entries! Quite a shame.
But there are several onomatopoeic verbs for making a low growling sound, such as ἀρῥάζω (arrházō), "to go arrha". Arrha, with a long, extended trill, sounds fairly close to a purr.
For a usage example, here's Aelian:
While checking something in the queror entry in OLD, I just happened to glance down and see querquēdula, 'a kind of water-fowl, prob. the teal.' It's not exactly a barnyard animal, though. Or maybe it would hang out with the ducks – or I should say other ducks, since the teal is a type of duck.
Otherwise, aside from quadriiugus and quadrupes, there's also ...
Maybe dedecus familiae, the shame of or to the family (e.g. Cicero pro Cluentio).
C. D. Yonge translates Cicero's original dedecus familiae as "disgrace of his family", which is what a black sheep means.
It seems that interbreeding between wolves and dogs was deemed possible in Roman culture at least at the time of Pliny the Elder (I cent. CE.) But so was the idea of interbreeding between dogs and tigers.
I was curious and went to Pliny's Naturalis Historia.
It happens to have separate chapters for wolves and dogs. The latter happens to mention wolves and.....
I always liked Horace's simile comparing Chloe to a fawn in Odes 1.23:
Vitas hinnuleo me similis, Chloe,
quaerenti pavidam montibus aviis
matrem non sine vano
aurarum et siluae metu.
nam seu mobilibus veris inhorruit
adventus foliis seu virides rubum
et corde et genibus tremit.
atqui non ego te tigris ut ...
It's normal, it happens but even if there's an anomaly, it's in Greek, not in Latin.
The story behind this is that actually quite often cognates (word of common origin) designate related yet different concepts in related languages, and zoology terminology is no exception.
The Latin word is reconstructed from from Proto-Indo-European, here's an excerpt ...
In Petronius, Satyricon 64, Trimalchio's favorite, Croesus, has an 'indecently fat black puppy' (catellam nigram atque indecenter pinguem) named Margarita, which means 'pearl', and Trimalchio himself has a dog, the 'bulwark of the house and household' (praesidium domus familiaeque) named Scylax, which is Greek for 'young dog' or 'puppy'.
In the meantime, ...
Martial wrote a poem about Publius' dog called Issa. It begins:
Issa est passere nequior Catulli,
Issa est purior osculo columbae,
Issa est blandior omnibus puellis,
Issa est carior Indicis lapillis,
Issa est deliciae catella Publi.
Issa is naughtier than Catullus’ sparrow,
Issa is purer than a
Issa is more winning than ...
Three examples I have just now come across (edit make that four examples - see "owl" below):
Lucius, having been turned into a donkey tries to draw attention to his plight, by calling upon the name of Caesar:
Et “O” quidem tantum disertum ac validum clamitavi, reliquum autem
Caesaris nomen enuntiare non potui.
And indeed I shouted “O” by ...
I second the recommendation of avis nocturna. (It would also be possible to say nocturna avis.)
If you wanted something more poetic, you could also go with something like avis tenebrosa, which would translate to something like "gloomy bird" or "bird of gloom" or "dark bird."
As Aristotle is generally considered as the father of biology — Darwin wrote: “Linnaeus and Cuvier have been my two gods… but they were mere school-boys to old Aristotle.” (in a letter to W. Ogle, 1882) —, it is logical to search for such a definition in his works.
According to Pierre Pellegrin (in particular in Une zoologie sans espèce, 1984), the ...
Horatius describes a "combined animal" with human's head, horse's neck, bird's feathers and fish's rear end.
This creature ends in a fish: instead of legs it presumably has a fishtail.
No details of the fish are given; just that the creature contains a fish-like part.
The translation available at Perseus (the Latin version is there, too) puts it like this:
DuCange reports qualea (quail) with qualia (!) and quaquilia as alternate spellings. The work cited by DuCange, by Johannes de Janua, better known as Johannes Balbus (d. c. 1298), explains that the bird got its name from the sound it makes, "quaquera". Possibly this was a medieval development, as in classical Latin, this bird would be called a cōturnīx—...
No, the form is accidental. Instead it's onomatopoeic, which can be deduced by it's cognates in:
Greek ololyzein [ὀλολύζειν], Sanskrit ululih "a howling," Lithuanian uluti "howl," Gaelic uileliugh "wail of lamentation," Old English ule "owl".
Greek diminutives aren't formed by a lambda. That Latin's diminutives do is coincidence.
[so far, up to entry group 8 of around 70 in L&S, currently in 'im-' in alphabetical order. Most of letter i- is made of in-, which is dominated by in- and inter- prefixed words less likely to be animals]
Arguably common animals starting with i-:
ibex, -icis, m. a kind of goat, the chamois.
ictis, -idis, f. a kind of weasel. From Greek.
I believe volare is used indeed with various insects, such as bees, flies, and cicadas. From the HP corpus:
Publius Ovidius Naso, Ars Amatoria 1.95, 1.96:
Granifero solitum cum vehit ore cibum,
Aut ut apes saltusque suos et olentia nactae
Pascua per flores et thyma summa volant,
Sic ruit ad celebres cultissima femina ludos:
L. Iunius ...
superbis iuvenibus the 'proud young men' (dative pl) are described as
siccis herbis 'withered crops.' (1310 - 20 de Lisle Psalter:)
However, this is closer to "He's such a disappointment," than "The black sheep of the family." Alternatively,
impius, (3) undutiful (Ainsworth & Mead)
Filius impius in patrem (Tacitus)
After a quick review of letter Q in L&S, I only found what cnread found: querquedula, which is apparently a kind of duck.
Other near misses (besides the already mentioned quadrupes, quadriiugus and quadriga):
Quelea, scientific name Quelea quelea, an african bird, first described in the XVIII century by Linneus as a species, later become a whole genus, ...