There doesn't appear to be a backoff on this. If you try to login on the bird site it DOS's itself and just keeps sending requests until it dies. 

The error code changed. Now it's 429ing...

you don't say...

@runewake2 now the question is: if the client didn't back off on a 503, whether it would behave any different on a 429.
I don't think I'm going out on much of a limb to say it would surprise me if it did...