The Prothonotary warbler is sometimes called the swamp canary. These small birds are a brilliant yellow with bluish-grey green wings and a black eye that’s very striking on the yellow head. Males are a more intense yellow than females. The name is somewhat strangely pronounced as it comes from the word proto notary, a clerical rank in the Catholic Church whose members wear bright yellow robes. The swamp canary nickname is appropriate as these birds are indicative of a healthy environment, as the canaries in the coal mines were used to monitor for air quality. Although small, they are aggressive about their nesting sites, males fight to establish a territory, and after the nest is built, both parents engage in bill snapping to fend off intruders. They ‘re easy to spot -- they fly relatively low and their bright color catches your eye.
How to Spot a Swamp Canary

SC Public Radio