This thesis analyses yearly mark-recapture-recovery information collected over a 36- year period, from 1968 to 2003, for 23 686 flipper-banded Little Penguins Eudyptula minor of Phillip Island, in south-eastern Australia. Such a long-term data set is extremely rare for any species. Few studies of any animal have been able to model age dependence for the survival, recapture and recovery probabilities simultaneously. I successfully apply such a modelling scheme and obtain biologically realistic age structures for the parameters. I also provide illustrations of erroneous results that may arise when analyses fail to consider simultaneous age dependence, or fail to detect annual variations that may mask age dependence. I obtain a low survival estimate of 17% in the first year of life, increasing to 71% in the second year, and around 80% thereafter, and declining gradually after age nine years. First-year survival increases with number of chicks fledged per pair, increases with annual average fledging weight and decreases with mean laying date. An increase in first-year survival is associated with warmer sea surface temperatures in the summer and autumn of the previous year, which agrees with biological considerations. Irrespective of this inter-year variation, birds born early in the breeding season, relative to the rest of their cohort, have greatly enhanced first-year survival, when compared to birds born late in that season. Fledglings survive better in years in which the mean fledgling weight is higher, and fledglings of above average weight have a better chance of survival than their underweight counterparts. I next analyse seven years of recapture data from a separate experiment studying the effect of banding on adult Little Penguins. In the year following marking, the survival probability of banded birds is 6% lower than that of unbanded birds, while in subsequent years the survival is 4% lower for banded birds. Band loss is negligible. Finally, I compare the survival estimates for Phillip Island with those obtained for a six-year study in New Zealand. While first-year survival is significantly higher for New Zealand, there is a marked decline over time, coinciding with an increase in population size.