"We have found a compelling connection between changes in the calling dates of frogs and changes in local air temperatures," says James Gibbs of State University of New York in Syracuse, who did this work with Alvin Breisch of the New York State Department of Environmental Conservation in Delmar, New York. This work is in the August issue of Conservation Biology.
Long-term studies show that amphibians and songbirds are breeding earlier in Europe. Similarly, reports suggest that birds are arriving earlier, and mammals and wildflowers are emerging earlier in the U.S.
To assess climate change over the last century in the Ithaca area, Gibbs and Breisch used historical records of the average daily maximum temperatures from November through June, which are key months for the timing of frog reproduction. During five of these key months, the temperatures increased about 2 to 4 F. To determine the earliest calling dates of six frog species in the area, the researchers used existing studies of two time periods: 1900- 1912 and 1990-1999.
The researchers found that four of the species (spring peeper, wood frog, gray treefrog bullfrog) are calling 10-13 days earlier, while two (green frog, American toad) have not changed their earliest calling dates.
Climate warming will probably have little impact on most of the frogs studied because Ithaca is in the middle of their breeding ranges. However, climate warming could affect species at the edges of their ranges. For example, while the current southern limit for mink frogs is about 90 miles north of Ithaca, warmer temperatures could rapidly push that limit northward. "Mink frogs would be expected to show predictable, local declines if local climate warming continues," caution Gibbs and Breisch.
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