A possible resolution and denouement would be that once Mitch leaves his hometown with his family and Marion, the birds' attacks heighten in violence and they end up exterminating one another. This could be backed up by the "lemmings over-the-cliff" idea that they "autodestruct" due to overpopulation. It would be nature's way of regaining balance and control.
Another option would be that once Mitch evacuates the village with his family, Marion, and the turtle doves, the aggressive birds mysteriously disappear, as if the very presence of these caged birds had incited the whole thing. I think this ending is more enigmatic and "sticks" better to the rest of the story. If you want to get really creepy, you could have a couple of bird "escapees" showing up again on a tree outside wherever Mitch, his family and the turtle doves are relocated. To make the nightmare continue in a truly "Hitchcockian" way....
As for symbolism, these attacks which seem against nature could symbolise another "act against nature," Mitch's overattachment and perhaps even Oedipal attraction to his mother. At least in the early film version, at first one is not sure whether she is Mitch's wife or mother. But the good relationship between the two women seems to refute this hypothesis, and it seems that Hitchcock was taking a certain poetic licence in presenting the film in such a way.
All of the characters are in need of love, belonging, or fear abandonment. You'll notice that each bird attack helps the characters bond and brings them closer and closer together. The wild birds represent nature's decomposers/life cycle, - natural forces indifferent to human life. These forces can be unpredictable and threatening to all. Melanie brings the caged love birds to the island. Love (the love birds) is a purpose of life that people give to one another, against the wild threat of nature and the abyss of eternity. It starts in the pet shop with Melanie and Mitch discussing the caged love birds, as nature's wild birds circle/swarm outside. Melanie finds her love in Mitch and vice versa. Nature (wild birds) strips away Melanie's exterior so that Lydia doesn't see her as a threat, and looks at her maternally with accepting care. Melanie is receiving a mother's love. The love birds initiate a bond between Melanie and Cathy as they were a wanted and appreciated gift. In the end as they leave as a bonded, caring unit against nature's threatening indifference to their existence, they take the love birds (both alive and unharmed). The love birds represent their love/caring for each other that each character has found. The love/bond each has found is the only thing left/worth taking with them as they move on. Emphasizing that in the end that's all there really is.
Most of Hitchcock's films concern themselves with the psychology of women in a state of existential fear. (Marny, Vertigo, Psycho (the dead mother)). In the Birds, Hitchcock shows this angst in the form of nature going awry: the attacking birds. This phenomenon begins at the point that Mitch's mother, who is desperately jealous of any femaie who might take her son's attention away from her, meets the attractive city girl bringing Mitch a pair of love birds. As this young woman takes the boat back to Bodega Bay, the first bird strikes her (this bird being an extension of the mother's violent fear of this threatening female). As the film develops and Mitch becomes more entangled with the young woman, the birds become more violent. They kill another contender for Mitch's heart, the school teacher. Only in the end, when the mother realizes that Mitch truly cares for this woman, and she herself feels pity for the attack the woman suffered from the birds, does the mother let go of her son, and the birds quieten down.
No references.....just what I got from watching it again after many many years!
Birds are the most blessed beautiful creatures in the world. Bird watching is one of my favorite pass time. I use to watch the bird from my windows, it is beautiful scene when it is viewed through binoculars. Bird watching binoculars are available for the exclusive viewing of the birds.