Penguins swimming prowess cost them their ability to fly, a new study says,
Brian Handwerk
for National Geographic
Penguins lost the ability fly eons ago, and scientists may have finally figured out way. A new study suggest that getting off the ground eventually just took too much effort for birds that were becoming expert swimmers.
Flight might make some aspects of penguins antartic life much easier. The grueling march of the emperor penguins, for example might take only few easy hour rather than deadly days. Escaping predators like leopard seals at the water edge would also be easier of penguins could take flight, so scientists have often wonderred why and how the birds lost that ability.
A popular theory of biomechanics suggests that the birds once flight adapted wings simply became more and more efficient for swimming and eventually lost their ability to get penguins off the ground.
More efficient diving, on the other hand, incresed the opportunities to forage for food at depth. A modern emperor penguin can hold its breth for more than 20 minutes and quickly dive to 1,500 feet (450 meters) to feast. The new study of energy costs in living birds that both fly and dive provides critical evidence to back up this theory.
"Clearly, form constrains function in wild animals, and movement in one medium creates tradeoffs with movement in a second medium," study co-author Kyle Elliott, of the University of Manitoba, said in a statement.
Sit, Swim, and Fly
The thick-billed murre or brunnich's guillemot (Uria lomvia) uses its wings for diving much like penguins, but it also flies. scientists theorized that its physiology and energy use may closely resemble those of the last flying penguin ancestors.
Other swimming birds can be considered biomechanical models for the lifestyle energy reveals why today's penguins are grounded. guillemots dive more efficiently than any other flying bird and are bested in diving only by penguins themselves according to the study.
Flight, however, costs them more energy than any other known bird or vertebrate and has become difficult to maintain. The team examined thick-billed murres at acolony in Nunavut, Canada, and pelagic cormorants at Middleton island, Alaska. They injected the birds with stable isotopes of oxygen and hydrogen to serve as tracers to mark the physical cost of their activities. The team also fitted them with time-budget devices that track those activities recording movements, speeds, and other data much like pedometers do.
"Basically the birds do only three things : sit, swim, and fly. So by measuringlots of birds and combining their time budgetbith the total costs of living from the isotope measures, it is possible to calculate how much each component of the budget costs,"explained stydy co-author John Speakman, who leads the Energetics Research Group at the University of Aberdeen, Scotland.
"The assumption is that (penguins) evolved from an auk-like ancestor," Speakman contnued.
"This would involve a progressive reduction in wing size, which makes diving more efficient and flying less so. Penguin bones also thickened over the ages, as lighter bones that make it easier for birds to fly gave way to more dense bones, which may have helped make them less buoyant for diving," But Speakman believes the wing changes were the primary adaption.
