There is an ongoing study of birds at the Panola Mountain State Park in Rockdale County, Georgia located on the outskirts of Atlanta. Panola Mountain State Park is 1600 acres and features an erosion resistant granite monadnock, wetlands, lakes, and a restored grassland. Farmland and a golf course were converted to a grassland starting in 2001 by removing non-native plants and planting native bluestem grasses that originally occurred throughout much of the state. Periodic controlled fires help maintain the native landscape. The grassland is surrounded by forests.
191 species of birds are known to occur in the park and 90 species have been banded here. Scientists capture birds with mist nets that they set up at least once a month from morning until noon, and they’ve been doing this since 2007. The most recent study analyzed evolutionary changes in the birds that live in the park either seasonally or year-round.
Map showing location and banding areas in Panola Mountain State Park. It’s located on the outskirts of Atlanta. From the below referenced study.
Graph showing average annual temperature increase over the past 17 years from a nearby weather station. Also from the below referenced study.
There is an erosion resistant granite monadnock in the park. I will probably visit this park some day.
Restored grassland in the park where birds are captured and studied.
Western palm warblers migrate through the park.
Indigo buntings live year-round in the park. They are vicious little birds. I saw one chasing another bunting into a window. It pecked the stunned bird in the head until it was dead.
Field sparrows and other species of sparrows thrive in the restored grassland.
Average annual temperatures at this locality have increased by 4 degrees F over the past 17 years, according to data from the nearby Jonesboro weather station. Scientists expected changes in local birds that followed Bergman’s Rule and Allen’s Rule. Bergman’s Rule states that species of animals in warmer climates will grow on average to a smaller size than those same species that occur in colder climates. Allen’s Rule states that species of animals in warmer climates will grow longer appendages than their northern cousins. Scientists captured 2,938 birds including 668 recaptures for the body size part of the study. They analyzed 9 species. Gold finches, field sparrows, and savannah sparrows grew smaller wings in contradiction to Allen’s Rule. The other 6 species had unchanged wing lengths. Bergman’s Rule was contradicted by data from 4 species. Scientists hypothesize local variations contributed to these contradictions. Birds often live for part of the year in other locations that may have had different temperatures.
1,128 birds including 45 recaptures were used to study the migratory phenology (the time of year when birds begin their migration). They found 1 species did have an earlier spring migration and 2 species started migrating later in the fall. The study also looked at demographics. 1 species had a higher male sex ratio than previously, and another species had a higher population of juveniles than formerly.
The authors of this paper believe restoring grasslands can help mitigate the detrimental effects of climate change because they see so little change here. In my opinion that is a stretch. It’s a relatively small sample size from just 1 location, and climate has always changed, and those changes are not always detrimental.
Reference:
McMahaon, A.; K. Stumpf and C. Muise
“Changes in Morphology, Phenology, and Demography of Several Avian Species over 18 Years at a Restored Grassland”
Georgia Journal of Science 83 (2) 2025
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