In a low hesitating voice Pippin began again, and slowly his words grew clearer and stronger. 'I saw a dark sky, and tall battlements, ' he said. 'And tiny stars. It seemed very far away and long ago, yet hard and clear. Then the stars went in and out - they were cut off by things with wings. Very big, I think, really; but in the glass they looked like bats wheeling round the tower.
Pippin, confessing to Gandalf after taking the Palantír...
The Lord of the Rings, The Two Towers, Book Three, Chapter XI The Palantír
There's one mention of bats in LotR.