Good looks are not a prerequisite to a faithful relationship. In fact, black vulture society makes sure of that. They have been known to attack other vultures that have been caught philandering!
Researchers even looked at genetic evidence from DNA fingerprinting to study the black vulture's monogamy. A study published in the journal Behavioral Ecology found that "mated pairs exhibit long-term pair bonding and year-round association, and share incubation and nestling feeding duties equally." Couples that parent together stay together.