Balwyn meeting report, 23 February 2016
Speaker: Andre Chiaradia
It is always a delight to hear news of our Little Penguins. Research Scientist Andre Chiaradia works at Phillip Island Nature Parks and his focus is prey-predator relationships using Little Penguins as an ecological model. He has discovered much about Little Penguins’ foraging behaviour and he came to tell us about this and their current challenges.
Being birds, penguins have to come on land to lay their eggs so they have to survive in two ecosystems – land and sea. And as top predators they are vulnerable to changes in those ecosystems. They are very comfortable at sea; agile swimmers, but are awkward on land. We have two close populations, the St Kilda and the Phillip Island groups. The St Kilda group spend all their time within Port Phillip Bay allowing thorough study of their biology. Currently penguins are moulting, a period of about 17 days when they stay on land, fast, lose all their feathers and are generally miserable. Over winter they regain weight and body condition. Males are 10% heavier than females except just before breeding in spring. Females lay two eggs of different quality: egg A has much higher energy nutrients than egg B and the resultant chick is much more likely to survive. Incubation to fledging is about 90 days. Parental care tends to be unequal but a highly successful breeding pair – super achievers – may exhibit more equal chick care in good years. Worldwide penguin populations are in decline but the breeding success at Phillip Island is improving. The current population is 28-32,000 and increasing.
Fish remain at their one preferred temperature so as the ocean warms up in summer they tend to move away from penguins’ foraging zone, and the penguins at Phillip Island have to forage further. Water temperature also varies with depth. Warm layers lie atop cold layers and the narrow interface where the temperature changes rapidly between the two is called a thermocline. Fish love to gather in a thermocline, and the penguins are on their tail. El Nino years cause disruption of the water column. It seems that thermoclines disappear and penguins find it much more difficult to find prey. More frequent El Nino years add more foraging inefficiency.
Marine productivity is highest in spring. Little Penguins’ breeding success depends on biological variables and environmental variables. Their biology was carefully studied to explore what initiates the breeding phase, and nothing revealed the trigger. Andre’s group began to look carefully at the environmental variables in Bass Strait. They studied the ocean currents, temperature, salinity etc. and found that egg laying coincides with the annual rise in sea temperature in spring, which in turn is tied to a spike in chlorophyll A, a marker of marine nutrients. Northern hemisphere puffins behave exactly the same.
Two of Andre’s students studied the feeding behaviour of the St Kilda Little Penguins. The team managed to obtain data from the Spirit of Tasmanian ferry, which daily samples the waters of Port Phillip for salinity, temperature, marine productivity and turbidity. They fitted data loggers with a GPS to penguins’ backs to find where they forage. This showed that they fed in two areas, near St Kilda and out in mid-bay; these zones exhibited lower salinity, higher temperature, higher marine productivity (prey items) and lower turbidity. Little Penguins are visual feeders so of course they choose clearer water away from the Yarra River mouth. Prey items comprise squid, krill, sea horse, sardines, tiny barracuda and large numbers of jellyfish, the last being highly nutritious.
The penguins spend 80% of their life at sea. The Little Penguins at Phillip Island spend 50% of the winter inside Port Phillip Bay. There are activities within the bay which may disturb their life cycle, such as fishing, transport and dredging. We humans must manage this area so that Little Penguins can thrive, and with the help of data loggers, GPSs and scat DNA studies, Andre’s group has a good handle on what the penguins eat, where and when. As a result, activities within important feeding areas can be restricted. Looking at the bay in total, Little Penguins are a very small player in a large ecosystem. However as part of Victoria’s economy they punch well above their weight.
Andre acknowledged a big team of colleagues, both here and internationally, who are studying the biology and ecology of our local Little Penguins; and we appreciate their successes.
All photographs courtesy of Phillip Island Nature Parks
Contributor: Daphne Hards