Nifty, we had a great horned owl down on our property. We took it to a conservation agency where it later died of West Nile. We were put in touch with Penn State University lab folks and they came out to our property and tested for West Nile, which came back negative. No other questions or investigations thereafter, however they did tell me to feel free to contact them with any concerns/questions.
I would get it tested for your own peace of mind..you want to know your area is safe and if its not, then they treat the area to rid the mosquitos. I highly doubt they will confiscate your chickens for that, as they are used as sentinals. They may ask to use them in their program, if anything....but you have to give permission for that.
And I agree, I would not panic thinking AI. Birds die for all kinds of stuff. It could have been a young fledgling that didn't get off the ground fast enough and your chickens caught it. Many other things could have been cause of death. I personally think the tests are worthwhile.
Jody