Animals too have their square pegs in round holes; ostriches wish they were horses, squirrels flit birdlike in the tree-tops and whales would prefer to be fish. Perhaps the most extreme rejection of their ancient heritage is found among penguins. They see themselves as dolphins.
Aping sea mammals was an excellent career choice for penguins; most of the 19 species are thriving. However, ‘the times they are a changing’ and things may be less rosy in future, or so a paper in the October edition of Scientific American argues. In The Strangest Bird, R. Ewan Fordyce and Daniel T. Ksepka discuss the evolution of these iconic birds. The title is apt; penguins are an odd bunch. Flightless and fat, they travel the oceans, plunge diving for fish and krill. Two satellite-tagged Magellanic penguins covered 300,000km in nine years. Meeting up each summer to breed, they were declared, last week, to be ‘the most monogamous creatures on earth’.
Penguins breed in the most inhospitable places. The emperor species, a most awkward walker, nests tens of kilometres from the sea on the Antarctic ice-cap, where no mammal, apart from ourselves, dares venture. Birds are more warm-blooded than other creatures. Why do they choose to live in such places? The penguins’ ancestors turned their wings into flippers, converted their feather covering into a fur-like coat and solidified their bones, making them heavier. But when did these changes occur and what environmental forces drove them? Until recently, we knew little about penguin origins. Fordyce’s interest in his ‘strange bird’ began during the 1970s when he found a fossilised leg bone in New Zealand. He was not the first person to make such a find. That distinction goes to an unknown Maori who stumbled on a bone in the 19th Century. The fossil record remained sparse until the 1970s but, over the next four decades, more specimens came to light. Analysis of these suggests that the penguin story began 62 to 58 million years ago, soon after a catastrophe which wiped out most creatures on Earth, including the dinosaurs. Penguins come from one of the few surviving bird species.
The original ones were about the size of a cormorant and, according to Fordyce and Ksepka, the seas in which they evolved were warm. Over the next 37 million years, their descendants spread around the world and colonised even warmer regions. Fifty extinct species have been named.
Although some of today’s penguins live in warm latitudes, we associate these species with colder regions of the southern hemisphere. Why they came to live in such inhospitable habitats remained a mystery until Ksepka noticed something odd about the leg bones of the fossils. There were grooves running along some of them but not along others. The groovy bones were from birds which lived up to 58 million years ago. Those without grooves were older.
Heat loss through bare parts is a problem for birds. The arteries carrying blood to the feet of water birds are located beside the veins which return the blood to the heart. The arterial blood transfers heat to the returning flow, reducing energy loss. The grooves in the ancient bones, Fordyce and Ksepka argue, functioned in a similar way; the bones served as heat exchangers. But why, if the original seas were warm, was heat retention so necessary?
Cooler waters hold more oxygen and support a greater diversity of life. There must have been cold-water up-wellings in the ancient seas. The early penguins, the authors claim, moved to these cold spots for the extra food they provided. Exploiting cold waters became a penguin speciality and, in more recent times, they moved to the chilly southern oceans.
But Fordyce and Ksepka are pessimistic about the penguin’s future in rapidly warming seas. The Galapagos penguin thrives in the cool waters of its equatorial archipelago. However, in El Nino years, warm currents engulf the region and the birds’ fortunes go into reverse. Food availability is reduced, breeding fails and few young fledge.
With the onset of global warming, will penguins be able to adapt to warmer seas quickly enough to survive?