Penguins and environmental change

Forest and Bird, Issue 280, 1 May 1996, Page 11

Penguins and environmental change

Ange Davidson

ANALYSING parenting skills seems to be a’90s phenomena and, last summer, Adelie penguins were up for assessment. Rather than positive affirmations and anger management, the penguins were being judged on their foraging efforts amongst Antarctica’s pack ice. Growing interest in the commercial harvesting of krill in the Ross Sea prompted New Zealand scientists to begin studies of penguin colonies in 1981. Krill is the staple of the Southern Ocean’s food chain and the results are proving to be even more valuable than first thought. Adelies are an ideal species for the study. They spend the breeding season on land and are dependent on one key food

source — krill. Over half of the world’s Adelie penguins breed in the Ross Sea and Landcare scientist Kerry Barton says the birds provide a good indicator of environmental changes such as global warming and krill population dynamics. While warmer temperatures during the 1980s caused the total Adelie population to increase, the three colonies on Ross Island responded in different ways. At the small Cape Royds and medium-sized Cape Bird colonies, easy access to open water within the sea ice pack caused populations to increase dramatically. However, the large Cape Crozier colony, with 150,000 breeding pairs, experienced only a very small rise in numbers, and Barton believes the penguin population here is limited by the available krill. Sea ice is the critical factor for the smaller colonies and when it is slow to break up, open water may be 40 kilometres away. Parents take it in turn to lurch across the well tracked sea ice to forage and then return to feed their chicks. Walking costs penguins far more energy than swimming and much of the food collected at sea is expended in the journey. A bar-coded tag is injected under the penguin’s skin to identify individuals. The information tells Barton how long the bird spends feeding, while a weighbridge lets her know how much food it is bringing back. Another method for measuring foraging effort is a quick

stomach pump for parents returning from feeding. A blow for the hardworking parent and waiting chick, but the contents confirm the penguins’ dietary reliance on the smaller of the two krill species. North of Ross Island, on the Antarctic Peninsula, Adelies favour the larger of the krill species. Decline here in Adelie and increases in chinstrap penguin colonies in recent years seem to match other indicators of regional warming. Adelies prefer to forage in the pack ice, while chinstraps compete best in open water. Warmer temperatures have moved the ice edge further south and increased the distance between the peninsula colonies and the open areas within the pack ice favoured by Adelies. The melting pack ice has also pushed the larger of the two krill species further offshore. This information will help to develop a global model of Adelie penguin colonies, as indicators of the health of the Southern Ocean.