Enormous grounded icebergs and an unprecedented amount of sea ice in Antarctica's Ross Sea have nearly isolated one of the continent's most populous Adelie penguin colonies, making it difficult for the birds to return from their feeding grounds in the open sea, according to researchers funded by the National Science Foundation (NSF).
The numbers of Adelie penguins at Cape Crozier, about 130,000 breeding pairs in most years, "are at the low side" of the normal range, said David Ainley of H.T. Harvey & Associates of San Jose, California. A smaller colony of Adelies at Cape Royds will "fail totally" this year, he added.
Meanwhile, a small colony of about 1,200 Emperor penguins at Cape Crozier failed to raise chicks, according to Gerald Kooyman of the Scripps Institution of Oceanography. He said the birds probably abandoned efforts to breed when the icebergs, pushing southward, destroyed and closed off their usual breeding area. Those that did breed, and attempted to hatch the egg or raise the chick in the area, failed during incubation or soon after hatching.
The icebergs are designated B-15A and C-16. Iceberg B-15A is 37 kilometers (20 nautical miles) wide and 87 kilometers (47 nautical miles) long. Berg C-16 is roughly 18.5 kilometers (10 nautical miles) wide by 55 kilometers (30 nautical miles) long. The icebergs broke away from the Ross Ice Shelf in March 2000 and gradually migrated west to a point northeast of McMurdo Sound, creating a barrier that altered wind and current patterns.
Early this season, the sea ice extended roughly 128 kilometers (80 miles) north of McMurdo Station, the main U.S. research station in Antarctica, located on Ross Island. At this time of year, the ice edge typically extends between 24 and 32 kilometers (15 and 20 miles) north of the station. Recent storms have reduced the extent of the ice greatly; it now extends 61 kilometers (33 nautical miles) from McMurdo.
The extensive sea ice has increased the distance between the breeding colonies and food sources in the open sea. The birds must now walk rather than swim to their colonies. Their average walking speed is roughly 1 to 2 kilometers (.6 to 1.2 miles) per hour. They can swim at an average of 7 to 8 kilometers (4.3 to 4.9 miles) per hour.
The Adelie colony at Cape Crozier is the sixth largest in the world. The Emperor Penguin colony is one of the smallest for that species, at about 1200 pairs, but was the first discovered. Members of explorer Robert Falcon Scott's expedition first visited the colony at the beginning of the 20th century.
A classic story of Antarctic science and adventure, "The Worst Journey in the World," by Apsley Cherry-Garrard includes a description of an attempt by three men of Scott's party to collect the first Emperor penguin eggs from Cape Crozier. Early in the 20th century, the eggs were scientific curiosities because Emperor penguins were incorrectly thought to be a "missing link" between dinosaurs and birds. The researchers survived horrendous blizzards, confined for several days to a shelter they had erected in haste, in order to bring back the eggs.
The Adelie colony at Cape Royds is the longest-studied in Antarctica. Next to it is a hut erected by Ernest Shackleton during his first Antarctic expedition early in the 20th century. The colony has been monitored annually since 1959 by scientists from Landcare Research NZ and, most recently, by Ainley's group.
The colony had been increasing in recent years because sea ice had been dissipating. It is the southernmost Adelie penguin colony in the world, and its existence is now in jeopardy.
Researchers supported by the U.S. Antarctic Program have banded Adelie penguins at Cape Crozier and elsewhere on Ross Island with individual numbers, allowing them to be identified at a later date. The penguins' response to the icebergs likely will provide major new insights into the biology, resolve and resilience of this species.
NSF manages the U.S. Antarctic Program, which coordinates most U.S. scientific research in Antarctica.
Materials provided by National Science Foundation. Note: Content may be edited for style and length.
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