BBC Leaves Out Major Factor Behind Emperor Penguin ‘Wipe Out’
Thousands of emperor penguin chicks drowned when the sea-ice on which they were being raised was destroyed in severe weather.
The catastrophe occurred in 2016 in Antarctica’s Weddell Sea.
Scientists say the colony at the edge of the Brunt Ice Shelf has collapsed with adult birds showing no sign of trying to re-establish the population.
And it would probably be pointless for them to try as a giant iceberg is about to disrupt the site.
The dramatic loss of the young emperor birds is reported by a team from the British Antarctic Survey (BAS).
Drs Peter Fretwell and Phil Trathan noticed the disappearance of the so-called Halley Bay colony in satellite pictures.
It is possible even from 800km up to spot the animals’ excrement, or guano, on the white ice and then to estimate the likely size of any gathering.
But the Brunt population, which had sustained an average of 14,000 to 25,000 breeding pairs for several decades (5-9% of the global population), essentially disappeared overnight.
Emperors are the tallest and heaviest of the penguin species and need reliable patches of sea-ice on which to breed, and this icy platform must persist from April, when the birds arrive, until December, when their chicks fledge.
If the sea-ice breaks up too early, the young birds will not have the right feathers to start swimming.
This appears to have been what happened in 2016.
Strong winds hollowed out the sea-ice that had stuck hard to the side of the thicker Brunt shelf in its creeks, and never properly reformed. Not in 2017, nor in 2018.
Dr Fretwell said: “The sea-ice that’s formed since 2016 hasn’t been as strong. Storm events that occur in October and November will now blow it out early. So there’s been some sort of regime change. Sea-ice that was previously stable and reliable is now just untenable.”
The BAS team believes many adults have either avoided breeding in these later years or moved to new breeding sites across the Weddell Sea. A colony some 50km away, close to the Dawson-Lambton Glacier, has seen a big rise in its numbers.
Quite why the sea-ice platform on the edge of the Brunt shelf has failed to regenerate is unclear. There is no obvious climate signal to point to in this case; atmospheric and ocean observations in the vicinity of the Brunt reveal little in the way of change.
But the sensitivity of this colony to shifting sea-ice trends does illustrate, says the team, the impact that future warming in Antarctica could have on emperor penguins in particular.
Research suggests the species might lose anywhere between 50% and 70% of its global population by the end of this century, if sea-ice is reduced to the extent that computer models envisage.
Strangely the BBC forgot to mention the key factor. This is the Abstract of the Fretwell & Trathan paper: (my bold)
Satellite imagery is used to show that the world’s second largest emperor penguin colony, at Halley Bay, has suffered three years of almost total breeding failure.
Although, like all emperor colonies, there has been large inter-annual variability in the breeding success at this site, the prolonged period of failure is unprecedented in the historical record. The observed events followed the early breakup of the fast ice in the ice creeks that the birds habitually used for breeding.
The initial breakup was associated with a particularly stormy period in September 2015, which corresponded with the strongest El Niño in over 60 years, strong winds, and a record low sea-ice year locally.
Conditions have not recovered in the two years since. Meanwhile, during the same three-year period, the nearby Dawson-Lambton colony, 55 km to the south, has seen a more than tenfold increase in penguin numbers.
The authors associate this with immigration from the birds previously breeding at Halley Bay. Studying this ‘tale of two cities’ provides valuable information relevant to modelling penguin movement under future climate change scenarios.
The paper goes on:
The breeding failure and reasons for relocation are almost certainly linked to the early breakup of sea ice at the Halley Bay site (Barbraud & Weimerskirch 2001, Barbraud et al. 2011), but exactly why that breakup occurred is unknown.
It is interesting that the first year of poor sea-ice conditions immediately followed the strongest El Niño in over 60 years, one of the most positive values of the Southern Annular Mode (SAM) and a record low sea-ice year for Halley Bay. ….
The authors describe an unprecedented three-year period of breeding failure at the large Halley Bay emperor penguin colony. They link this to a dramatic rise in the population of the nearby Dawson-Lambton colony, a rise that can only have occurred due to immigration from Halley.
These changes have been driven by a change in sea-ice conditions and an early breakup of fast ice on the northern side of the Brunt Ice Shelf, which may be due to ENSO events and/or ice-shelf morphology.
The exact cause of the ice break up may not be known, but it seems highly likely that the record El Nino was a major factor, as well as other natural factors.
Collapses of emperor penguin colonies like this one aren’t unheard of. For instance, the colony at Cape Crozier was virtually wiped out in 2002, when a giant iceberg blocked the bay.
The same colony was also said to have shrunk drastically between the first visits by the Discovery expedition in 1902, and the Terra Nova one in 1910.
It is estimated that there are 595,000 emperor penguins, and they are spread pretty much all around Antarctica. It is well established that when colonies die out, most penguins move to other locations.
The media love to portray these events in emotional, humanized terms – “thousands of emperor penguin chicks drowned”
Unfortunately, though, this is nature in action.
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