Isidore of Seville [7th century CE] (Etymologies, Book 12, 6:13): Corvi [sea-ravens] are named from the sound of their breast [a cordis voce], because they croak in their breast and, betrayed by their characteristic sound, they are captured. - [Barney, Lewis, et. al. translation]

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Fish 7.27): The sea-raven is so called for its voice, as Isidore says, for it grunts in its chests and with its voice it is caught. But they signify certain impatient people, who, though outwardly disguising their impatience in their work, yet inwardly murmur in their hearts, and by this means are often caught in the devil's snares. - [Badke translation/paraphrase]