Based on information presented at the Global Change and Global Science: Comparative Physiology in a Changing World conference, August 4-7, 2010 in Westminster, Colorado.
Photo:Budgerigars killed by a heat wave on a ranch in western Australia in 2009 courtesy of Blair Wolf.
Blair Wolf, an associate professor of biology at the University of New Mexico, and Andrew McKechnie at the University of Pretoria in South Africa have been studying how desert bird populations might respond to global warming.
According to a press release from The American Physiological Society (www.the-aps.org),
increases in air temperatures of just two degrees Fahrenheit is sufficient to cause the rate of water loss to double in small birds like the small parakeets called budgerigars shown in the photo, or "budgies" as the locals refer to them. This change in water loss can greatly impact their ability to survive.
When environmental temperatures rise, birds must get rid of the environmental heat through evaporation across the skin and panting. Their ability to cool down is therefore lower with excessive water loss to the environment, resulting in higher body temperatures and heat stroke, causing tissue and organ damage and eventually death.
Wolf and McKechnie have used mathematical models to predict the future water costs of birds living in heat waves in the 2080's compared to the current costs in Yuma, Arizona, USA and Birdsville, Australia. Their research has predicted that smaller birds will have greater water losses compared to larger birds resulting in a reduction of survival rates by 30-40% in the small birds.
This is not good news for budgies and other small birds.
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Interesting article. I guess this selection pressure would drive smaller birds to evolve larger bodies - assuming the timeframe of the climate change was sufficiently protracted. Is there any good palaeontological and palaeoclimatological data correlating high global temperatures to avian body size?
There is an interesting paleontology study of penguin fossils that showed the penguins were indeed larger in the warmer periods of Earth's history(Eocene and Oligocene)compared to modern times. (Clarke et al., Paleogene equatorial penguins challenge the proposed relationship between biogeography, diversity, and Cenozoic climate change. PNAS. 104(28): 11545-11550, 2007).
the rate at which these climatic changes are taking place is much too rapid for natural selection to be able to act upon advantageous alleles and save these populations. there have also been observed die-offs of ostrich and peacock, as well as in a large species of fruit bat(flying foxes)in India this year. body size clearly isn't the only factor.