Will All Animals Shrink Under a Warmer Climate?

By Allison Bond | August 12, 2009 3:08 pm

jacky winter birdRising temperatures in Australia have caused birds on that continent to shrink–some by nearly 4 percent. The findings of a study published in the journal Proceedings of the Royal Society B are the first to show that birds’ sizes are affected by global warming, although this phenomenon previously has been shown in fish and Soay sheep. Scientists postulate that the relationship between a warmer climate and smaller animals may be true for the animal kingdom as a whole.

Temperature has a clear impact on body size; it’s old news among scientists that birds closer to the equator evolved to be smaller than their peers near the poles.  One possible explanation for this, called Bergmann’s Rule, is that larger animals conserve heat more efficiently, and this trait is naturally selected for in colder climates, but not in warmer climates. On this basis, scientists have predicted that climate change will affect the way animals vary in size at different latitudes [ABC Science]. The recent research on sheep and fish has corroborated this hypothesis by showing that these animals have become smaller as temperatures have risen.

By examining the skins of more than 500 southeastern Australian songbirds that were collected between 1860 and 2001, the research team found that wing length–a good measure of body size–decreased by between 1.8 to 3.6 percent, depending on the species. ”It is certainly a significant change,” said [co-author Janet] Gardner. ”Some declined in size more dramatically than others, but all the species were showing the same trend.” During the century Australia’s mean temperature rose by 0.7 degrees [The Sydney Morning Herald]. The scientists found no evidence that the decrease in size was due to nutritional changes among the birds.

Although there appears to be a short-term ability among certain animals to adapt to a warming climate, scientists aren’t sure how changing body size will affect animals, such as birds, in the future. “We don’t know how much a species can adapt to global warming and that of course is a very important question given the rate of warming is predicted to increase. How small can a bird go before its physiology is altered to the point where it can’t survive?” [ABC Science], says Gardner.

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Image: flickr / Lip Kee

CATEGORIZED UNDER: Environment, Living World
  • amphiox

    Interesting. But what about the association of vertebrate gigantism in the fossil record, like the titanosaurs of the early Cretaceous, and the giant mammals of the Eocene, and Titanoboa, etc with periods of warmer than average climate?

  • Jumblepudding

    perhaps warmer climates=larger cold blooded animals, smaller warm blooded animals and vice versa. I wonder if reptiles in Australia have become any larger.

  • amphiox

    Possible, but that doesn’t factor in the large Eocene mammals like Indricotherium. And the jury’s still out on what kind of metabolism the sauropods and other giant dinosaurs had.

    There’s even some evidence of humans getting larger body size during a warm interglacial period some 500 000 years ago or so. (That would be H. erectus, of course, a population that appears to have an average height well over 6 feet during the time period in question, though there remains the good chance that as more fossil evidence comes to light the apparent size discrepancy will turn out to be an artifact)

  • Gareth

    The difficulty I have with this is that the entire Australian ecosystem has changed since 1860 – Native grasses systematically enhanced with higher nutritional value introduced species, Deforestation, and irrigation are but three. The statement “The scientists found no evidence that the decrease in size was due to nutritional changes among the birds” is surely not sustainable in light of the fact that most native species have had to make dietary adjustments due to the changing face of the Australian eco system since European colonisation.
    In the stated case of Sydney bird sizes vs those of Brisbane, Since 1860 Sydney has become the biggest city in the country with a corresponding increase in pollutants and descrease in vegetation. I would be more interested in a correlation of bird size reduction for The two sites and also for a few non-urban sites.

  • Bob

    Of course this is absolute rubbish once again from scientists paid off by the wall street thugs who are set to have a field day in profits from carbon trading.
    If birds are smaller in warmer climates?
    Lets look at Tropical birds like Macaws, they are very small aren’t they?
    What about Condors and African Vultures?
    Eagles that live in the Desert?
    Clearly the Scientists who made this lie up should be fired and have their scientific credentials stripped from them.

  • Arbitrary Arbiter

    Yay Bob.

  • http://clubneko.net robot makes music

    Correlation does not imply causation.

    For instance, if the birds are dying younger from the hazards of urban living, they will reproduce younger, and their species size will shrink in stature.

  • vanderleun

    Yet anøther item to be filed under “Science Made Stupid.”


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