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Butterflies linked to climate change

Butterflies are emerging up to 10 days earlier in spring than they did 65 years ago.

March 18, 2010

By Bridie Smith, The Age Melbourne.

As Melbourne warms, the city's butterflies are emerging at least 10 days earlier in spring than they did in 1945, according to research that reveals for the first time a causal link between increasing greenhouse gases, the city's warming environment and the timing of a natural event.

Using emergence data on the common brown butterfly dating back 65 years, researchers from Melbourne University said the findings were unequivocal.

''There's very little room to doubt that now,'' said lead author Michael Kearney, of the zoology department. ''Animals are doing things earlier because the climate is warming, because of human activity.''

The findings, published in a Royal Society journal, Biology Letters, yesterday, showed that for each degree the air temperature warmed, the adult common brown butterfly would emerge 10 days earlier.

Dr Kearney said the study, which relates specifically to Melbourne, would prove a practical tool to forecast the impact of climate change on the city's biodiversity. ''We are able to make a very specific prediction about how things would change in the future,'' he said.

The findings would translate to other butterfly species, triggering a ripple effect through the ecosystem. ''There are likely many species which interact with the common brown butterfly because it's so abundant,'' he said.

''That may cause problems for species that are dependent on it.''

The scientists, participating in a research project in collaboration with Monash and La Trobe universities, hand-raised more than 1000 caterpillars for the study, observing each stage of development in temperatures from 8 to 30 degrees.

Dr Kearney said there were different rates of survival and development according to temperature, but significantly none of the caterpillars survived temperatures above 25 degrees and none of the eggs survived at 30 degrees.

Professor David Karoly, of Melbourne University's school of earth sciences, used four models based on natural and man-made warming influences to pin down the cause of the city's rising temperature.

''When he put the greenhouse gas emissions into the simulation it showed exactly the warming that we've got,'' Professor Kearney said.

The common brown butterfly's emergence also features on the Wurundjeri calendar, marking the start of the orchid season in September when the orchids and silver wattles are flowering and the koalas begin mating. ''That particular season is now occurring 10 days earlier,'' he said.

''It shows that there are all sorts of different biological events that define these seasons.''

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