Download Emergence of intense corvid predation on little penguin nests

ORAL ABSTRACT
Emergence of intense corvid predation on little penguin nests
Duncan R. Sutherland1, Kasun B. Ekanayake2, Peter Dann1, Michael A. Weston2
1
Research Department, Phillip Island Nature Parks, Cowes, Victoria 3922, Australia, 2Centre for Integrative Ecology,
School of Life and Environmental Sciences, Deakin University, 221 Burwood Highway, Burwood, Victoria 3125,
Australia
Nest predation is a major cause of reproductive failure among birds, and can drive prey population
declines. Here, we describe novel predatory behaviour of a corvid (little raven Corvus mellori) that has
recently emerged, leading to widespread and intense predation of eggs of little penguins (Eudyptula minor).
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. Little ravens congregate to coincide with the timing of penguin egg laying in the areas where
penguins breed, but not when and where alternative seabird species nests were available.
Through the use of cameras and direct observation, we identified that 61% of monitored burrows (n = 203)
were depredated by ravens, the only predator detected by camera traps. Analysis of burrow characteristics
revealed two distinct types of burrows, only one of which was associated with egg depredation by ravens.
Clutches destroyed by ravens were in burrows with wider and higher entrances, thinner soil or vegetation
layer above the egg chamber, shorter and curved tunnels and greater areas of bare ground and whitewash
near entrances. In addition, 86% were covered by vegetation through which ravens could excavate. Ravens
used two modes to access the eggs: they attacked through the entrance (25% of burrow attacks, n = 124);
or dug a hole through the burrow roof (75% of attacks, n = 124). 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. Burrows that were subject to attack through the entrance had significantly shorter tunnels than
burrows accessed through the roof.
The high rates of clutch loss recorded here highlight the need for population viability analysis of the
penguin population to assess the effect of egg predation on population growth rates. The foraging niche of
a corvid described here may have implications for burrow-nesting species worldwide where corvid
populations are increasing, as they exhibit great capacity to adopt new foraging strategies to exploit novel
prey.
9th International Penguin Congress, Cape Town, South Africa, 5th – 9th September 2016