Although the bestiary actually covers beasts, birds, reptiles, fish, and even a few insects and precious stones, bird symbolism deserves its own brief comment--especially since the publication of Beryl Rowland's Birds with Human Souls. In it she discusses the general patterns of bird symbolism: "The idea that the bird represented the soul as opposed to the body, the spiritual in contrast to the earthly, seems to have been universal." In addition the bird was associated with new life and procreation. In medieval art the bird is also a frequent inhabitant of paradise or the garden of earthly delights while a few birds may point to negative qualities in man or represent the Seven Deadly Sins. In art there are numerous depictions of the Christ Child clutching a bird in his hand or holding a bird on a string--both suggesting the idea of the soul incarnated in the body.
In the bestiaries we learn of the phoenix who possesses both sexes in itself and who at the end of its life builds a funeral pyre. It then ignites the fire, burns itself up, and on the ninth day rises again from the ashes to live another life. Given these fabulous details, it is small wonder that the Christian allegorists saw the phoenix as a symbol of Christ and his resurrection from the dead. References to particular birds in literature often bring a deeper meaning to the text. For example, Chaucer characterizes his Squire through the nightingale, a traditional symbol for lust and sexual love. Ironically enough, the nightingale's song could also be associated with Christ's death and resurrection and thereby with divine love.
Friedmann, Herbert. The Symbolic Goldfinch. Bollingen Series no. 7. Washington, D.C.: Pantheon Books, 1946.
Focusing on the history and significance of the goldfinch in European devotional art, this source gives in detail the symbolism of the bird and discusses the types of pictures in which it appears. It also includes notes, index, bibliography, and plates.
Ingersoll, Ernest. Birds in Legend, Fable and Folklore. New York: Longmans, Green and Co., 1923.
Organized around broad themes, this source covers material from east, west, ancient, and modern. Although it has no footnotes, it generally tells where material comes from.
Rowland, Beryl. Birds with Human Souls. Knoxville: The University of Tennessee Press, 1978. (I have)
This is clearly the standard source to consult. Based on solid research and well-written, this book covers the major birds, with a thorough explication of each. It includes a full bibliography.