How do I know how old birds live?

I wrote a blog post about Ruffed Grouse in 2018, mentioning that the oldest Ruffed Grouse on record lived to be just 8 years old. Someone commented today, asking how I know that. We get information about each species longevity records from the USGS Bird Banding Laboratory in Patuxent, Maryland. Their website, where you can find this kind of information, is here: https://www.pwrc.usgs.gov/bbl/longevity/Longevity_main.cfm