Gift ideas -- choicest new books for the holidays; Dogs, cats, birds in Venice; A Venetian Bestiary, by Jan Morris. New York: Thames and Hudson. 128 pp. $14.95.

Although Jan Morris concedes in the introduction that she has ''written rather too much'' about Venice in the 35 years since the city ''first bewitched'' her, this fanciful newcomer is unlike any of its predecessors. While other nations often have identified with one animal, Venetians have adopted entire flocks and herds with a tender, childlike innocency that Morris captures here in art and real life. She shows us beasties romping on the columns of the Doge's Palace, sea birds swooping through the mosaics of the Basilica, barge dogs standing proudly in their prows, pigeons cooing in the Piazza San Marco, and cats snoozing in upturned gondolas.