Penguins are dependent on waterproof plumage for survival. The molt in sub-Antarctic penguin species is a seasonal and catastrophic process during which the animals go through periods of fasting and high levels of stress. Their entire plumage is usually replaced in 3 wk. Attempts at consistent hormonal induction of molt in penguins have been unsuccessful. Four Yellow-eyed Penguins ( Megadyptes antipodes ) were referred for treatment at Wildbase, Massey University, Palmerston North, New Zealand, in late April 2014, following loss of waterproofing, feather breakage, increased body weight, pododermatitis, and damage to caudal feathers from hock sitting. Feather plucking of damaged areas to stimulate feather regrowth was attempted with poor results. Waiting 10-12 mo for a natural molt was not tenable. Catastrophic molt was induced by treatment with 10 g/kg of fresh beef thyroid gland orally once a day. The molt was complete in 18-26 d during which the animals regained full plumage and waterproofing after feather regrowth. The forced molt feathers had abnormal pigmentation but were of sufficient quality to allow release of the birds back to the wild.