NEW YORK, Jan. 30 (Xinhua) -- Scientists have found that rising temperatures might lead to smaller body sizes of birds, which raises worrisome implications for the health of birds on a warming planet.

A new study, conducted by an Australian research team and recently published in the journal The Auk: Ornithological Advances, suggested that exposure to excessive heat might have a stronger impact on birds' body size than bitter cold.

Researchers captured and measured about 40 adult house sparrows at each of 30 locations across Australia and New Zealand, finding that sparrows are more likely to be smaller in places with hot summers than extreme cold weathers.

Nestlings that mature in warm places grow into smaller adults, and they stay that way even if they also live through cold winters, the study said.

"This might be an adaptive response, and may make animals better able to cope with changing conditions," Simon Griffith, a senior author of the study and a researcher at Macquarie University in Sydney said.

Doctoral candidate Samuel Andrew, leading author of the study, agreed with Griffith, saying: "If these changes in size are an important part of adapting to warmer climates, then birds that don't change their size in response to temperature change could be the species that are more vulnerable."