The crimefighting partner of Nightingale.
Sunbird has the ability of flight as well as projecting light, possibly from her costume or equipment instead of being innate.
Besides their partnership as crime-fighters, casual observations suggest that there is more to the relationship between Sunbird and Nightingale. Perhaps romantic in nature, or that they are sisters, or even daughter and mother. Sunbird does appear smaller and younger than Nightingale.
Based on a partially blocked headline reading "Darklings Crushed by Sunhawk and Nightingale," it very likely means that Sunbird has changed her codename at some point over the years.