On the basis of the findings of a CSIRO-funded one-of-its-kind study, evolutionary biologist Dr Janet Gardner - of Canberra's Australian National University - and her team said that Australian bird species are 'shrinking' in size, largely because of rising temperatures.

Published in Proceedings of the Royal Society B, the study, which measured the wing length of 517 museum specimens over time, revealed that eight species of south- eastern Australian songbirds had changed in size during the last century - with the size of some birds shrinking by nearly 4 percent! On an average, the birds had shrunk by between 1.8 percent and 3.6 percent.

The eight songbird-species studied by the researchers included - brown tree-creepers; white-browed scrub wrens; variegated fairy wrens; jacky winters; grey-crowned babblers; speckled warblers; yellow-rumped thornbills; and hooded robins.

Remarking that shrinking was an evolutionary response to rising temperatures, Dr Gardner said that though the change in size of the birds may seem rather trivial, "it is certainly a significant change. Some declined in size more dramatically than others, but all the species were showing the same trend."

Noting that Australia's mean temperature increased by 0.7 degrees during the last century, the researchers said that the findings of the study indicate a "generalized response" by the eight avian species to the major environmental changes, like global warming.