Eudyptula minor as a species is very fragile. Even in studies where populations lived without predation or human impact, the death rate of clutches remained at a high 42% with 69% of fledgling not being able to reach maturity (Reilly 115 and Muller-Schwarze 168). Most deaths occur because of the birds' diet and the availability of food. For instanced in years when Australia and New Zealand experienced weather changes associated with ENSO (El Nino), which affects the availability of fish for the penguins, the populations suffered not only in the mortality of adults but in an increase of the mortality rate of all stages of maturity. External parasites such as ticks contribute largely to the deaths of immature penguins. Natural predation by sharks, gulls, and seals also act as natural controls on the penguin's population (Reilly 116).
Additionally, on Phillip Island, cool water temperatures brought on by the Melbourne West Wind bring added nutrients that aid the production of food and success of clutches. In years when the West Wind is weak, spikes in mortality similar to El Nino years can be seen (Reilly 115).
Food availability and storms are the main cause of death and crashes in the penguin's population; however, these are natural controls and are completely non-human. |
