Their travel companions also include Donnie, a feral boy whom the Thornberrys adopted, and Darwin, a skittish chimpanzee.
Eliza, the younger of the two sisters, has a magical ability to communicate with animals, the origin of which is explained in the season 2 episode "Gift of Gab".
Unlike typical Nickelodeon series of the time, each episode is a full half-hour in length (22 minutes if not counting commercials).
The Thornberrys get word that the only way to save the funding for their show is to film a segment about the black rhino, Eliza, Darwin, and Donnie find it.
When the Commvee is put out of commission they take a small steamer boat named Prudence up the river in search of the otter.
Debbie, Eliza, Tyler and Darwin head to the market while Nigel, Marianne and Donnie go off to film in an ancient crater.
The kids take off in pursuit of the merchant who is now driving their comvee to try and reach an understanding with him, but not before running the gauntlet of the local monkeys.
The Thornberrys are in Tanzania, Africa to film the grand opening of Dr. Jane Goodall's chimpanzee sanctuary.
When they arrive, Debbie is put to work caring for baby chimps in the nursery while Eliza and Dr. Goodall have an awkward first meeting.