Louis is a young Trumpeter Swan born without a voice. Unable to make the standard vocal sounds of his species, he faces severe communication barriers within his family and the wider natural community. He is highly intelligent and determined, deciding to attend a human school to learn reading and writing to compensate for his speech defect. He carries a slate and chalk around his neck to interact with humans while searching for a way to communicate with his own kind.

Sam is an 11-year-old boy who feels completely at home in the natural world. He respects wildlife deeply and prefers quiet observation over disturbing the animals he watches. He keeps a private journal where he writes daily summaries, usually ending with unanswerable questions about life and his future. He steps in to protect the swans from a predator, forging an unusual bond with the avian family.

The Cob is a large male Trumpeter Swan and father to a brood of cygnets. He speaks in poetical monologues and views his children as an extension of his own pride. When he discovers his son cannot speak, he vows to help him communicate, willing to risk his own safety and honor to acquire a human instrument for his voiceless child.

The Swan is the practical counterweight to her husband's theatrical behavior. She approaches parenting with straightforward common sense, focusing on necessary tasks rather than grand declarations. She relies on keen observation and is the first to correctly diagnose her son's inability to speak.

Serena is a young female Trumpeter Swan. Following her natural instincts, she ignores courtship attempts that lack the traditional swan call. She travels along standard migration routes but eventually finds herself in an unfamiliar human environment during a severe storm.

Mrs. Hammerbotham is a teacher at the local school in Montana. She initially rejects the idea of allowing a bird into her classroom, arguing that literacy is reserved exclusively for humans. She enforces strict classroom rules but shows a willingness to adjust her views when presented with undeniable evidence of intelligence.

Mr. Brickle is the director of Camp Kookooskoos, a summer camp for boys. He oversees daily activities and hires a bugler to play standard camp calls. He is fair-minded and expects his campers to show basic respect to all staff members, regardless of their species.

The Boatman operates the Swan Boat ride in Boston. Recognizing a lucrative business opportunity, he hires a live musician to swim ahead of his boat and entertain passengers. He advocates fiercely for his employee, even arguing with hotel staff to secure proper lodging for the performer.

Abe "Lucky" Lucas is a slick nightclub promoter operating in Philadelphia. Dressed in purple suits, he acts as a booking agent who secures lucrative but loud club residencies for his clients, always ensuring he takes his ten percent agent's fee.

The Head Man in Charge of Birds manages the avian population at the Philadelphia Zoo. He believes strongly in keeping wild birds safe in captivity by surgically pinioning their wings so they cannot fly away. He enforces strict, rule-bound policies but occasionally recalls the idealism of his own youth when pressed.

Mr. Beaver is a genial father who regularly takes his son on camping trips to the wilderness. He trusts his child's capabilities, allowing the boy to hike alone with only a compass for guidance. He provides a foundation of safety without prying into his son's private discoveries.

Mrs. Beaver manages the household at the Bar Nothing Ranch in Montana. She demonstrates practical boundaries when her son brings an unusual guest home, firmly insisting that wild animals sleep in the barn rather than the house.

Applegate Skinner is a camper at Camp Kookooskoos who loudly proclaims his dislike for birds. He struggles to fit in and is occasionally mocked by other campers for his name, leading him to take reckless actions on the lake in an attempt to prove himself.