From Phrases, Cliches, Expressions on www.joe-ks.com:
For the birds
Meaning: Something that is worthless.
Origin: Before the advent of cars, one could
see and smell the emissions of horse-drawn wagons in New York. Since
there was no way of controlling these emissions, they - or the
undigested oats in them - served to nourish a large population of
English sparrows. If you said that something was for the birds, you're
politely saying that it's horse crap.
apology, after his deliberate and harmful actions, was for the birds
in everyone else's eyes.
...and then there are the following two quotes from the Bible which if interpreted the same way, would put the usage way before the 20th century:
Isaiah 18:4 For this is what the Lord has told me: “I will wait and watch from my place, like scorching heat produced by the sunlight, like a cloud of mist in the heat of harvest.” 18:5 For before the harvest, when the bud has sprouted, and the ripening fruit appears, he will cut off the unproductive shoots with pruning knives; he will prune the tendrils. 18:6 They will all be left for the birds of the hills and the wild animals; the birds will eat them during the summer, and all the wild animals will eat them during the winter.
Jeremiah 16:4 They will die of deadly diseases. No one will mourn for them. And they will not be buried. Their dead bodies will lie like manure spread on the ground. They will be killed in war or die of starvation. And their corpses will be food for the birds and the wild animals.
(from the website: 10000birds.com as an answer to the question, "Why is 'for-the-birds' a bad thing?")