Miner's canary
Canaries were once regularly used in coal mining as an early warning system. Toxic gases such as carbon monoxide and methane in the mine would kill the bird before affecting the miners. Because canaries tend to sing much of the time, they provided both a visual and audible cue in this respect. The use of so called miner's canaries in British mines was phased out as recently as 1987.
Hence, the phrase "canary in a coal mine" is frequently used to refer to a person or thing which serves as an early warning of a coming crisis. By analogy, the term climate canary is used to refer to a species that is affected by an environmental danger prior to other species, thus serving as an early warning system for the other species with regard to the danger.
Use in research
Canaries have been extensively used in research to study neurogenesis, or the birth of new neurons in the adult brain, and also for basic research in order to understand how songbirds encode and produce song. Thus, canaries have served as model species for discovering how the vertebrate brain learns, consolidates memories, and recalls produces coordinated motor movements. Fernando Nottebohm, a professor at The Rockefeller University detailed the brain structures and pathways that are involved in the production of bird song.
Trivia
Canaries have been depicted in cartoons from the middle 20th century as being harassed by domestic cats; the most famous cartoon canary is Warner Brothers' "Tweety Bird".
Norwich City, an English football team is nicknamed 'The Canaries' due to the city once being a famous centre for breeding and export of the birds. The club adopted the colours of yellow and green in homage.