The term 'fly-by-nighter' refers to someone who is unreliable or untrustworthy. The crossword solutions BAT, REDEYE, OWL, and HOOTOWL all refer to animals that are associated with this term. A BAT is a nocturnal mammal that is often seen as a symbol of darkness and mystery. A REDEYE is a type of bird that is known for its distinctive red eyes and its ability to fly at night. An OWL is a nocturnal bird of prey that is associated with wisdom and intelligence. A hootowl is a type of OWL that is known for its loud hooting call. All of these animals are associated with the term 'fly-by-nighter' because they are active at night and can be seen as symbols of unpredictability and unreliability.