In Vayikra 11:19, the atalef is listed as an unclean bird. Is it not a bat which is a mammal/rodent? Is this a translation issue?
It is certainly not a translation issue, as it might be considered a bird by the Torah (by virtue of the fact that it flies), which does not need to follow any modern-day taxonomy, as stated in the comments...
(If we want to get really crazy we can apply the famous rule of Dibra Torah Kelashon Benei Adam, the Torah speaks in man's language, to say that the Torah would call any flying creature a bird even though Hashem knows it is not a bird, so the people living at that time would understand it. The usage of this term in contexts like this is a subject of much debate, and IIRC it was discussed in the first issues of Dialogue magazine.)
Additionally, here are a few recent blog posts that deal with the identification of the Atalef according to Chazal, some of which suggest that it may not be a bat, and what it might be instead: