Having exhausted the fruit and berry crops of their Nordic homelands, waxwings are heading southwards, writes Richard Collins.
The threat of starvation drives these bohemian migrants to our shores. In previous ‘waxwing winters’, the visitors found sanctuary in Irish hedgerows and gardens. There is food for them again this time around, but such ‘eruptions’ aren’t always rewarded.
For some creatures in our rapidly changing world, traditional journeys in search of food can end in disaster, as a research project described in the journal Current Biology shows.
Penguins breed around the southern tip of Africa and on its west coast north to Angola. The Cape Peninsula’s Boulder Beach, named for the 500 million-year-old granite rocks framing it, has a famous colony.
From the boardwalks, tourists view nesting ‘jackass’ penguins up close and personal. The black-and-white birds, 65cm tall and attired like the nuns of old, are aptly named; they hee-haw like donkeys.
Wishing they were dolphins rather than birds, penguins have disowned their avian heritage. With wings converted to fins, they abandoned flying. These pursuit-divers out-swim their fish prey. Though around since the time of the time of the dinosaurs, they are now falling on lean times; four of the world’s 17 species are classified as endangered.
The jackass penguin is the most recent addition to the casualty list. Millions of its eggs were harvested each year in South Africa, until commercial exploitation was outlawed in 1968. Removing guano, used as fertiliser, deprived the birds of essential nesting cover.
Then, in 1983, the first of several disasters struck; the Spanish tanker Castillo de Bellver exploded off the Cape’s west coast. Over 55,000 tonnes of burning oil blanketed the sea. Nine years later, the Chinese-owned MV Apollo Sea, sank near Cape Town with the loss of all 36 crew-members.
The arrival of oil-covered penguins on beaches was the first indication to rescuers that anything was amiss. In June 2000, another tanker, the MV Treasure, went down off Robben Island, killing over 19,000 breeding penguins.
Seabirds don’t recover easily from such calamities; they are slow to breed and produce few young each year. In 2010, BirdLife International declared that the jackass population had crashed by more than 50% in the previous 30 years. “This trend shows no sign of reversing,” it added.
The main threat to the jackass is commercial fishing. The species has been sliding towards extinction since industrial fishing started around the Cape, says BirdWatch South Africa. Scarcity of food is not the only issue; being unable to find the food which is available in the rapidly changing oceans, is just as big a problem.
Richard Sherley, and a team from the University of Exeter, fitted satellite trackers to 54 young jackass penguins. The trackers revealed that the birds swam westwards and northwards, covering thousands of kilometres in low sea temperatures. Like our waxwings, the penguins headed for traditional feeding areas, as their forebears had done.
Unfortunately, industrial fishing and climate change have decimated fish numbers at the old sardine and anchovy spawning sites. Over-exploitation off Namibia has led to a collapse in the sardine population, while rising sea temperatures and changes in salinity have driven the fish northwards.
The sardines have been replaced by jellyfish and low-energy gobies. As a result, the unfortunate birds have moved into, what the researchers call ‘marine ecological traps’ where many of them starve. The survival rate of young penguins is greatly reduced.
“Similar traps could be operating elsewhere,” the paper concludes, and with future climate change likely to exacerbate matters, “management actions that alleviate, and ultimately remove, fishing pressure at low biomass, should be implemented”.
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