Australian birds shrink to cool off

Australian National University
ScienceAlert 14 Aug 09;

Australian birds have dwindled in size over the last 100 years and climate change appears to be to blame, say researchers from the Australian National University and CSIRO.

“Using museum specimens, we measured changes in the size of eight Australian bird species, and found that they have become smaller by 2 to 4 per cent, over time. That doesn’t sound much but it’s a significant change,” said research leader Dr Janet Gardner from the Research School of Biology at ANU.

Birds, like other animals, tend to be smaller in warmer climates, because smaller bodies lose heat more quickly than larger bodies. As a result, individuals of the same species tend to be larger near the poles and smaller near the equator.

“We looked at size patterns of individual species across South-eastern Australia and found that these gradients have shifted because birds are getting smaller as temperatures rise. Birds of a size once found near Brisbane now occur in Sydney, 7 degrees further south,” Dr Gardner said.

The researchers measured the brown treecreeper, grey-crowned babbler, hooded robin, speckled warbler, jacky winter, yellow–rumped thornbill, white-browed scrubwren, and the variegated fairy-wren.

They found that the birds appear to be adapting to global warming by getting smaller, thus minimizing the costs of heat stress. “We’d like to look at a broader range of species to see if the same pattern of size changes is evident,” Dr Gardner said.

“How much and how rapidly a species can change in response to rising temperatures remains to be answered,” she said.

The findings are published in the journal Proceedings of the Royal Society London. The research team included Dr Leo Joseph at the Australian National Wildlife Collection, CSIRO Sustainable Ecosystems and Associate Professor Robert Heinsohn at the Fenner School of Environment and Society at ANU.

The work was funded by the Australian National Wildlife Collection Foundation.
Editor's Note: Original news release can be found here.