Published on August 15th, 2013 | by Jo0
Maths and Penguins: the effect of climatic conditions on Little Penguin survival
The Phillip Island Penguin Parade is the second largest natural tourist attraction in Australia, with 525,000 tourists witnessing the captivating spectacle of up to 3000 penguins returning from the sea at dusk in 2012-13. In order to ensure the longevity of the Little Penguin (Eudyptula minor) colony, it is essential to be able to monitor trends in their survival probability in the wild. One of the major areas of study for penguin researchers in Australia is predicting the potential effect of climatic conditions, and climate change, on Little Penguin survival and ultimately on population size. This is where mathematics comes into play!
Little Penguins on Phillip Island have been marked since 1968, first with individually-numbered metal flipper bands and later with injected electronic transponders. This provides us with the rare opportunity to investigate the relationship between penguin survival and climate over a relatively long period. Using life-history data for Little Penguins, our group carried out a mark-recapture statistical analysis to examine if variation in sea-surface temperature (SST) and sea-temperature gradient (east−west difference between two locations in Bass Strait) affect survival probability in the first year of life. We found that first-year survival is correlated with an east−west sea-temperature gradient in Bass Strait in the winter after fledging (with an increased temperature gradient associated with decreased survival) and the mean SST in the autumn after fledging (with warmer seas associated with increased survival). Projections suggest that SST in south-eastern Australia and sea-temperature gradient in Bass Strait will both increase due to global warming. However, the net effect of an increased sea-temperature gradient in winter (which has a negative influence) and increased SST in autumn (which has a positive influence) on first-year survival is uncertain, given the current lack of knowledge concerning the relationship between the sea-temperature gradient and SST in Bass Strait.
Our group has also examined the seasonal effects of wind strength and direction on the survival of Little Penguins. This study was based on two key hypotheses: westerly winds bring cool nutrient-rich waters into the foraging grounds of the penguins (with a positive flow-on effect on the penguins’ food source), and strong winds cause turbulence and mixing in the water columns of the penguins’ foraging grounds (which can adversely affect the penguins’ foraging success leading to a negative effect on their survival). We found that an increasing number of days with strong westerly winds in autumn appear to have a negative effect on first-year survival. This is not surprising as autumn is a treacherous time for inexperienced newly-fledged birds. Adult survival was negatively associated with mean wind speed in autumn, which follows the annual moult when adults have to recover from fasting ashore for around three weeks.
Future research will consider the relationship between penguin survival and ocean temperature and wind speed in combination with other covariates such as chlorophyll-a which provides a measure of marine productivity. Stay tuned for further work in this area!
This work was conducted in collaboration with Dr Ted Catchpole (retired Statistician), Dr Peter Dann (Research Department, Phillip Island Nature Parks) and Dr Lynda Chambers (Centre for Australian Weather and Climate Research, Bureau of Meteorology). All penguin data were provided by Phillip Island Nature Parks, while climatic data were supplied by the Bureau of Meteorology.
The Applied and Industrial Mathematics (AIM) Research Group in the School of Physical, Environmental and Mathematical Sciences at UNSW Canberra continues to use mathematics and statistics to study complex real-world problems.