The USGS in Alaska has been doing a long-range study of bill deformities, with no specific culprit named yet. The Cornell Lab requests reports of deformed beaks from anywhere in the US. Here are two good articles:
On Nov 29, 2012, at 9:43 AM, Josh Phillips wrote:
> This week we've had a large group of cardinals around the feeder and fruit trees in our yard in South Burlington. Among them is a female with a fairly severely damaged bill. Everything I can find online suggests avian pox as the culprit. Does anyone have experience with this? She seems otherwise healthy and must be eating somehow.
> More details and photos here:
> I'm planning to give the feeder station a good scrubbing this weekend.