Worthless, not to be taken seriously, no good. For example, This conference is for the birds—let's leave now. This term has been said to allude to horse droppings from which birds would extract seeds. This seemingly fanciful theory is borne out by a more vulgar version of this idiom, shit for the birds. [Slang; first half of 1900s]

Worthless: “The last scheme you came up with was really for the birds.”