In Scripture, there is mention of tanin (with a nun at the end) and tanim (with a mem at the end). The former is a generic term for serpentine/ monstrous creatures such as snakes, crocodiles, and whales (singular tanin, plural taninim). But what are the tanim (which, incidentally, is a plural form; the singular is tan)? The tanim are mentioned in several places in Scripture as creatures that live in ruins and desolate areas, along with birds called bnos ya'anah (ostriches or some kind of owl), and they are described as making a wailing sound. Thus far, they could be either jackals or a different type of owl.
There is one crucial verse which is thought to conclusively resolve this:
Even the tanin have bared their breast, nursing their cubs; yet the daughter of my people has become cruel, like ya’enim in the wilderness. (Eichah 4:3)In this verse, there is a kri/kesiv mesorah that the word written as tanin is to be read as tanim. There is reason to believe that this is the correct reading - no serpentine creature nurses its young. Thus, tanim are mammals. Hence, the tanim described elsewhere as wailing creatures of the wilderness must be jackals, not owls. That is why in modern Hebrew, jackals are called tanim.
This all seems straightforward. But there is an assumption being made here, which is not necessarily correct! The assumption being made is that the Scriptural writer knew which animals nurse their young and which don't. However, as Rambam and others make clear, the prophets (and even the Torah) speaks within the scientific worldview of antiquity. Thus, there is no reason to assume that the zoological description is necessarily accurate.
What does this mean with regard to tanim? One scholar, Othniel Margalith, argues that the verse in Eichah should be read as tanin - which matches the Septuagint's translation of draco (serpent). Margalith claims that this verse reflects a belief in antiquity that snakes nurse their young on milk. As evidence, he points to clay cobras from Beth Shean which are seemingly formed with breasts. Thus, the verse in Eichah is referring to snakes, and is not talking about the wailing tanim of the ruins that are mentioned elsewhere in Scripture. These can therefore be identified as some kind of owl.
While Margalith's view should certainly be taken into consideration, I don't know if it is necessarily correct. The interpretation of such clay figurines is debated; even if they do depict breasts, some argue that it may reflect artistic or idolatrous concepts rather than zoological beliefs.
(See too R. Yaakov of Lisa, Palgei Mayim (link: p. 171, second column, line 8), who, in a different approach, says that Chazal believed that snakes would take milk from women. I haven't been able to find any reference to such a thing in Chazal, and I would be indebted if anyone can point me to such a source.)
But Margalith's approach led me to consider another possibility. Even if the verse in Eichah should be read as tanim (and is referring to the wailing tanim of the ruins), does it rule out owls? As R. Josh Waxman pointed out in another context, there was an ancient belief in a strange type of owl called a strix, which was thought to nurse its young on milk.
There are advantages to positing that tanim are strix owls rather than jackals. Tanim are always translated by Targum Yonasan as yarudin, and the Talmud Yerushalmi (Kilayim 8:4) identifies these as birds. Thus, the most ancient traditions for the identity of tanim favors owls rather than jackals (whereas the earliest source for positively identifying them as jackals is Tanhum Yerushalmi, in the thirteenth century).
A further piece of evidence is that Gemara in Sanhedrin 59b mentions a “yarod nala”; according to Sokoloff's Dictionary Of Jewish Babylonian Aramaic, s.v. נלא, this refers to a demon or vampire. The strix was believed to be a demonic bird which sucked people’s blood, and thus this phrase in the Gemara is further indication that the yarod (which is the tan) is the strix.
Of course, it's still not absolutely straightforward. The verse in Eichah refers to the young of the tanim as gurim. This word is elsewhere used only to describe lion cubs, which would perhaps favor identifying tanim as jackals, which have cubs, rather than strix owls. Still, it seems that Chazal, at least, understood the term to refer to lactating vampirous strix owls. And one thing is clear: the identity of the tanim of Scripture is certainly not as straightforward as is often assumed.