Archive for April 2012
Penguins are amazing swimmers. There plump bodies and specialized feathers provide perfect streamlining – penguins create even less drag than computer models predict they should when cutting through the water. They also reach impressive depths. We see a lot of artwork of fossil penguins standing on land, but like modern penguins they were birds of the oceans. Below is a great reconstruction of Kairuku waitaki out at sea.
How well did giant penguins swim? This is an interesting question. At such different sizes and shapes, it is not safe to assume extinct species like Kairuku swam in an identical fashion to living penguins. In fact, some researchers have suggested that giant penguins were not as capable of diving as living penguins. This idea was based primarily on the flipper bones of some fossil species like Anthropornis, which were considered more angled than those of living penguins. However, the idea that giant penguins had to stay closer to the surface is wrong for three reasons. First, not all giant penguins have angled flippers. When the bones are articulated at their joints, some giant penguins show a strongly angle between the humerus and the more distal wing bones (those closer to the tip of the wing). However, in the species Icadyptes salasi the flipper skeleton is nearly straight when articulated. Not all giant penguins had the same type of flipper! Regardless, this is somewhat irrelevant to diving capacity. Many modern birds hold their wings in a partially folded position and still make it down to impressive depths. The Thick-billed Murre (a relative of puffins and razorbills), which weighs only about two pounds, can reach depths of up to 180 meters, angled wing and all. Perhaps the most compelling evidence that giant penguins were accomplished divers is the general relationship between size and diving depth in tetrapods. In marine birds and mammals, there is a very strong positive correlation between body mass and maximum dive depth. Provided penguins don’t “break the rules”, it’s pretty safe to assume giant penguins were capable of deeper dives than their living relatives. Emperor Penguins delve deep into the dark seas, and have been recorded foraying 500 meters below the surface. Amazingly, this record is a minimum estimate because the gauge recording the penguins depth broke under the pressure! I suspect Kairuku could manage similar depths, though of course most of the time this would not be necessary because much of its prey was probably higher in the water column.
Macquarie Island is an isolated island of the South Pacific, located roughly half-way between Australia and New Zealand and quite far to the south of both. The island is home to King Penguins, and recently a team of biologists published a study of ancient and modern penguin DNA from bones collected on the island, some of them up to 8,000 years old, to reconstruct patterns in genetic diversity in the early and modern history of this island.
These samples reveal patterns in genetic diversity of King Penguins over a period of great stress. Two King Penguin colonies were originally present on Macquarie Island. Sadly, human settlers wiped out all of the penguins in the colony at the Isthmus (the northmost part of the island) by 1894 and reduced the population at Lusitania Bay to about 3400 birds – a tiny fraction of the original population.
Sounds like the final days before a tragic loss of the entire islands penguin fauna. However, just in time, Macquarie Island was made a wildlife refuge in 1930. Over the next 80 years the penguins rebounded and some birds from the Lusitania Bay colony moved north along the coast and re-started the Isthmus colony. One of the interesting things that the DNA study revealed is that the penguin have reached levels of genetic diversity close to those that existed before human arrival. Genetic diversity is important. A plunge in the number of genotypes can leave populations vulnerable to genetic disorders carried on recessive genes. Higher genetic diversity also provides resilience to changing environments. While many ancient DNA studies have revealed that population crashes can result in genetic bottlenecks, the Macquarie Island penguins seem to have rebounded – possibly through fortuitous survival of genetically diverse individuals and perhaps also through arrival of a few King Penguins from other areas of the southern oceans.
Thanks to protections put in place, there are almost half a million King Penguins living on Macquarie Island today. A hopeful conclusion of this study is that even after being severely pressured, penguins can rebound if we just allow them the chance
Heupink, T.H., J. van den Hoff, and D.M. Lambert. In press. King penguin population on Macquarie Island recovers ancient DNA diversity after heavy exploitation in historic times. Biology Letters.