Leviticus 11:13,19 reads:
And these you shall detest among the birds . . . the eagle, the bearded vulture, the black vulture . . . and the bat. (ESV translation)
Does the bible describe bats as being a bird?
Modern science indicates that taxonomically speaking, bats aren't birds, but mammals.
The Hebrew word was used for winged creatures that weren't insects. Applying 'modern science' to an ancient culture's classifications of the world is anachronistic.
The Tyndale Bible Dictionary reads:
Modern scientists classify organisms on the basis of internal and external structure, but the biblical writers generally classified organisms according to habitat.1
1 Editors: Walter A. Elwell, Philip Wesley Comfort, Tyndale Bible Dictionary, p.215.
All citations are from the orignal Hebrew and Aramaic, not translations
In modern Hebrew, עטלף, the word to which I believe you are referring, indeed means bat. But Targum Yonason translates that word as טרפידא in Aramaic, which, based on the roots, (to capture prey by chasing it down and ripping it apart) leans more towards a sort of owl or other bird of prey that pounces on its prey with its talons, whereas bats, especially those found in the Old World, do not acquire their food in such manner:
Bats are the second largest order of mammals (after the rodents), representing about 20% of all classified mammal species worldwide, with about 1,240 bat species divided into two suborders: the less specialized and largely fruit-eating megabats, or flying foxes, and the highly specialized and echolocating microbats.[5] About 70% of bat species are insectivores. Most of the rest are frugivores, or fruit eaters. A few species, such as the fish-eating bat, feed from animals other than insects, with the vampire bats being hematophagous, or feeding on blood.
Abraham ibn Ezra explains on עטלף : "A small עוף (flying creature) that flies at night" - perhaps a bat, but could just as well mean a type of owl or other nocturnal bird of prey. RAMBAN (Nahmanides) on those verses explains that the underlying reason for the prohibition is that the species mentioned are birds of prey. (Clearly the other species mentioned in that verse are feathered birds.) Again, consistent with Targum Yonason, that would eliminate the bat, which is not a predator. except for the few species mentioned above, not found in the RAMBAN's proximity.
If the translation is indeed bat, then @MarkEdward's answer is obviously the correct one: Biblical Hebrew is not the language of modern taxonomy. However, that translation is arguably incorrect, (nor is modern, spoken Hebrew a reliable reference for interpreting biblical verses) and if we translate differently - owl - such as suggested, your question falls aside.
(That is not to say the bat is a kosher animal. As a rodent, it lacks the required characteristics - cloven hooves, chews its cud.)
