Mass loss, timing and duration of catastrophic moult in little penguins

Feather regeneration is vital for birds' thermoregulation, courtship, breeding, camouflage, and locomotion, with strategies reflecting life history. Little penguins (Eudyptula minor) use a 'catastrophic moult' strategy, replacing all feathers within a short timeframe while on land and not foraging. This study examined the 2015 and 2016 moult seasons on Phillip Island to explore factors influencing moult timing, duration, and mass loss. The median start date for moult was earlier in 2016 (~Feb 15th) than in 2015 (~Feb 24th), with year being the only significant predictor of moult start date. The median moult duration was similar in both years (18.0 days in 2015, 17.5 days in 2016), and start date was the only significant predictor of duration. Males experienced significantly greater mass loss than females, though no difference was observed between years. The duration of moult and start-of-moult mass were key predictors of mass loss, with longer moult and higher initial mass leading to greater daily mass loss. The timing and duration of little penguins' moult, along with the need for significant pre-moult mass gain, are likely influenced by external factors like local prey availability. Moult plasticity likely benefits little penguin survival.