Bats as birds
These are the birds you are to detest and not eat because they are detestable: the eagle, the vulture, the black vulture, the red kite, any kind of black kite, any kind of raven, the horned owl, the screech owl, the gull, any kind of hawk, the little owl, the cormorant, the great owl, the white owl, the desert owl, the osprey, the stork, any kind of heron, the hoopoe and the bat.
Hold up. The bat? Doesn't God know that bats aren't birds? Ha ha. This Judeo-Christian God is pretty ignorant of his own creations.
But I find the passage quite acceptable, on two related grounds. The first is purely translational. If the Hebrew word we translate as "bird" meant "all flying things bigger than an insect," bats would quite properly be included. (In a similar vein, the Greek word we translate as "hand" [χείρ] included the wrist. So most depictions of Christ's crucifixion show the nails through his palms, even though the Romans normally put the nails between the radius and the ulna, which could support more weight. Whether the wrist is actually part of the hand is a linguistic issue, not a biological one.)
I don't know Hebrew, and I don't know what the original text of Leviticus says. But regardless, I see nothing inherently wrong with having viewed bats as birds (or whales as fish*). In our post-Linnaean world, such categories seem decidedly strange. But historically people have categorized things in many ways for linguistic purposes. The resulting words are likely to serve their purposes as long as everyone agrees on their meanings.
By today's definitions, and for today's purposes, a bat is not a bird. A whale is not a fish. A wrist is not a hand. And a man is in truth an ape. But I won't criticize those who once had other definitions for other purposes. Questions of definition, like whether Pluto is a planet, are not questions of natural fact.
*Every translation I've seen of Jonah 1:17 says Jonah was swallowed by a big fish, not a whale. The story is often told with him being swallowed by a whale, however, and I can't see that it loses much from that.