How would I locate a m3u8 for https://www.allaboutbirds.org/cams/cornell-lab-feederwatch/?
I doubt you will find a direct m3u link. Looks like they stream to youtube and then use youtube to distribute their stream. That is way more efficient (for them) than directly hosting a stream.
Some quick web searching finds an open-source utility called Streamlink 2.0.0 that is designed to convert youtube livestreams into something more friendly for video playback. The thread below suggests a couple other packages as well that look promising. Regardless, you will need to piece together a discrete solution to make this work.