Why have 150,000 penguins mysteriously disappeared?

No bird breeds farther south than the Adélie penguin. Antarctica is a harsh habitat, but their fast swimming skills and colony-mentality has allowed these birds to thrive.

But scientists say 150,000 Adélie penguins have disappeared from their home on Cape Denison within the last five years.

The authors suggest the 150,000 penguins died after the B09B iceberg was lodged in the Commonwealth Bay in 2010, blocking the birds’ main food source. This water is rarely covered by sea-ice, making it ideal for their hunting of krill and fish. 

“Although Adélie penguins are able to breed successfully under a range of sea ice conditions, we believe the extensive fast ice at Cape Denison in 2013 was beyond that with which they could cope,” the scientists from New Zealand and Australia explain in their study published Feb. 2 in the journal Antarctic Science.

The iceberg’s arrival “dramatically increased the distance” adult Adélie penguins had to travel for food both for themselves and for their chicks waiting back at the colony. Because parents’ foraging trips were longer, “the chicks were fed less often and meal size was reduced as the adults required more of the food obtained to meet their commute to and from the colony.” 

Ice has blocked Adélies’ food source route before, the scientists acknowledge in their study. But the worst case in recent history occurred at Cape Royds in 1994, when the adult penguins had to walk across 24 miles of ice for food. By comparison, the travel distance noted by researchers in 2013-2014 at Cape Denison was over 37 miles.

“I don’t think any of us anticipated what we saw: the ground was littered with dead chicks and discarded eggs,” study co-author Chris Turney from the University of New South Wales Australia, told Live Science in an email. “What had been until recently a noisy, raucous colony was now eerily quiet. It was heartbreaking to visit.” 

Most importantly, the authors note, the penguins are not coming back to the Cape Dension area. All birds that were recorded in the authors’ census were affiliated with current nests, there were no ready-for-breeding birds. And if no new members join this local colony, it could die out in 20 years, say the authors. 

The researchers recognized some relocation in their census, with three percent of chicks immigrating to the Ross Island colonies, 12 to 30 miles away. And while this might spell the end of the Cape Denison colonies, similar relocation efforts will save the species as a whole. 

“Since the formation of fast ice in Commonwealth Bay a very high percentage of breeding attempts at Cape Denison have failed and this will doubtless continue until B09B breaks up or relocates and the fast ice dissipates,” the authors explain in their study. “Emigration from the smaller colonies east and west of Cape Denison may, however, delay local extirpation and could provide a mechanism for eventual recovery when B09B moves from Commonwealth Bay.” 

But some scientists aren’t buying it. Michelle LaRue, a penguin population researcher at the University of Minnesota who was not involved in the study, told Live Science that 150,000 Adélie carcasses have not been found so no one can know for certain what happened to these birds.

“Just because there are a lot fewer birds observed doesn’t automatically mean the ones that were there before have perished,” said Dr. LaRue. “They easily could have moved elsewhere, which would make sense if nearby colonies are thriving.” 

And as for the Adélie skeletons found by the researchers? Easily explainable, says LaRue. Because of the cold weather, carcasses don’t decompose: Adélie penguin colonies are always scattered with dead birds. 

Finally, even if 150,000 Adélies did perish, which LaRue doubts, it is “hardly apocalyptic.” As of 2011, seven million Adélie penguins were counted in Antarctica.