Posted on 07/12/2015 by Phillip Island Nature Parks
Little ravens learn to target penguin eggs
Little ravens have been shown to specifically target penguin eggs in a behaviour which appears to be only recently learned, according to a study undertaken by researchers from Deakin University and Phillip Island Nature Parks and published in Austral Ecology and Wildlife Research.
The study investigated whether little ravens, a highly intelligent species of bird, congregate in time and place to exploit eggs and chicks of little penguins, short-tailed shearwaters or silver gulls. It was found that the ravens’ presence coincided with the timing of egg laying for penguins and silver gulls, but not shearwaters. The ravens were also seen in greatest numbers in the areas where penguins breed, but not where shearwaters or silver gulls breed.
The study determined that the presence of penguin eggs in burrows correlated strongly with little raven activity, and this implies that little ravens may have learnt to exploit the plentiful food resource of little penguin eggs hidden within burrows.
Through the use of cameras and direct observation, the researchers were also able to determine that the ravens employed two main forms of attack. ‘Entry attacks’ accounted for about 25% of predation, where ravens would repeatedly thrust their beak in through the burrow entrance, sometimes over a period of several days, until finally the penguin guarding the eggs was unable to defend against the attack.
‘Digging attacks’ accounted for about 75% of predation, with ravens digging in through the roof of the burrow and harassing the penguin until it was unable to defend against the attack. On some occasions, ravens were observed to work in pairs, where one would dig through the burrow roof and one would distract the penguin at the entrance.
This behaviour has become apparent over the last 15 years of a 47 year study of the penguin colony on the Summerland Peninsula.
Dr Duncan Sutherland, Deputy Research Manager at Phillip Island Nature Parks commented: “This penguin colony is one of the largest in Australia and is a major ecotourism attraction, so threats to the population are of both conservation significance and economic importance. Current research seeks to determine how this emerging skill is passed between ravens and how raven predation might effectively be curtailed to maintain the viability of this important penguin colony.”