It's a really fascinating thesis, which is that humans are the only conspecific, the only species that can kill other members of the species from range.
Ruth actually carries around this little Bluetooth speaker and she plays what's called a conspecific Sparrow call, sort of like the standard call that we know will activate the other birds.
Was to see faces of other, what biologists call conspecifics, you know, and other same non-conspecific people, like people that could be romantic partners or family members or people we were going to work with.