Low survival rather than breeding success explains little penguin population decline on Granite Island

Over the past decade, populations of little penguins (Eudyptula minor) have been seriously declining across South Australia for reasons still not fully understood. In the present study, I investigated breeding performance and return rates of little penguins on Granite Island for 17 years in relation to patterns of population decline. I focussed on the impacts of human disturbance, breeding site, abandonment and predation on breeding success. The average breeding success was 1.05±0.12 fledglings per pair; and breeding success increased since 1990, despite population decline. Breeding site was the main factor affecting breeding success. I found no effect of predation or abandonment on breeding success, but there was a negative effect of predation on the number of dead chicks found. In addition, I found a negative effect of human disturbance. Despite the observed increase in breeding success, return rates were extremely low for both adults (16.3%) and fledglings (2.3%). Population modelling confirmed the observed population decline on Granite Island, with subadult survival being the most critical variable affecting population growth. The present study thus highlighted the need for further studies into factors affecting survival of adults and subadults.