There’s an article on getting DNA from vampire bat feces in Science Magazine here.
When I was an undergraduate at Cornell University, I worked on that topic for my undergraduate honors thesis. I extracted and sequenced DNA from the crap of vampire bats that fed on chicken blood. I was pretty excited after it finally worked after about 3 years without success. It was really cool to see another team finally doing what I wanted to do and apply this method to vampire bats living in places like the Amazon where they might be feeding on their original wild prey. See my previous post on this topic.
This team found that the vampires they caught were all still feeding on domestic animals though. It’s a neat study nonetheless.