New Study of Avifauna at Panola Mountain State Park

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

https://digitalcommons.gaacademy.org/cgi/viewcontent.cgi?article=2774&context=gjs

Cougars Kill California Condors

The California condor (Gymnogyps californiana) was the first species listed as endangered after the Endangered Species Preservation Act passed, and 40 years ago, there were so few, biologists captured the entire population, so they could be bred in captivity. Since then, wildlife officials have been releasing some back into the wild, and their numbers are slowly increasing. They still face a number of serious threats. When they scavenge animals killed by hunters using lead shot, they get lead poisoning. They also are poisoned when they consume rodents that died after eating poisoned baits. Windmills slaughter birds of all kinds. One year (2010), scientists found 3 condors killed by cougars (Puma concolor). Apparently, the condors were roosting in trees near a carcass they’d been feeding upon, and the cougars climbed into the trees and killed them in their sleep.

Scientists found 3 California condors killed by cougars in New Bitter Creek National Wildlife Refuge. Map from the below referenced journal article.

Evidence a cougar killed a condor. From the below reference.

The entire population of California condors was captured 40 years ago. Captive breeding brought them back from the edge of extinction but they still face some serious threats.

California condors released back into the wild may be naive to the threat of natural predators. Andean condors (Vultur gryphis) co-exist with cougars in South America, but there are few or no known cases of cougars preying upon them. Cougars benefit Andean condors because the birds scavenge upon llamas and deer killed by cougars. Flocks of condors may even drive cougars from their kills. (They are very large birds.)

During the Pleistocene California condors occurred all across North America, and fossil specimens have been found in New York and Florida. Following the extinction of Pleistocene megafauna, the range of the California condor shrunk to the Pacific coast where they survived by feeding upon whale carcasses. At first they benefitted from the arrival of Europeans because they scavenged all the dead livestock on the range. But lead poisoning from hunters’ shotgun shells soon began to take their toll.

Reference:

Branney, A.; J. Brandt, J. Felch, J. Lombardi

“Observations of a Puma Predation on Endangered California Condors: Implications for Species Recovery”

Ecosphere 16 (6) June 2025

https://esajournals.onlinelibrary.wiley.com/doi/full/10.1002/ecs2.70255

3 New Studies Support Human Overhunting as the Cause of Late Pleistocene Megafauna Extinctions

3 new studies support human overhunting as the cause of Late Pleistocene extinctions in South America, and perhaps the most interesting study is an isotopic analysis of the Anzick child’s remains. The Anzick child was an 18-month-old toddler deliberately buried after his death. The body was discovered in Wilsall, Montana during 1968 and was associated with over 100 Clovis artifacts. Radiocarbon dates suggest the toddler lived sometime between 12,900 years BP-12,695 years BP. In 2014 local Indian fanatics insisted scientists let them rebury the body because of their stupid religious beliefs, but genetic evidence suggests this tribe was not even directly descended from the baby’s parents. Instead, the baby was more closely related to Indians living in Central and South America today. Nevertheless, scientists still had isotopic data from the child’s bone chemical composition, and they were able to determine the baby’s mother’s diet. (The child likely still got most of his nutrition from nursing.)

Scientists used a statistical model of the isotopic composition to determine mammoth made up 35%-40% of the mother’s diet, showing that megafauna was the most important resource for the Clovis people in this region. Elk made up 15%-17% of their diet, camel and/or bison made up 21% of their diet, horse made up 6% of their diet, and small mammals only 4% of their diet. (Bison and camel had a similar diet, so scientists can’t distinguish their isotopic signatures.) The ancestors of the Clovis may have been generalist foragers who had already reduced populations of horses and camels, but they became big game hunting specialists during the Clovis era. This study also compared the Anzick child’s isotopic composition with those from other large carnivores that lived in the region then. The Clovis diet was most similar to that of the scimitar-toothed cat. This big, fanged cat is thought to have specialized in hunting juvenile mammoths. Archaeologists and anthropologists who proclaimed humans hardly ever hunted mammoth were certainly wrong. Large mammals were the central item in the diet of the Clovis culture, and humans surely overexploited them into oblivion.

Pie charts from the below referenced study (Chatters et. al.) showing the percentage of mammals that made up each species diet. Humans enjoyed a diet most similar to Homotherium–the scimitar-toothed cat. FYI, Arcotodus = short-faced bear, Aenocyon = dire wolf, Miracinonyx = psuedo cheetah, Canis = timber wolf, Panthera = giant lion, Bootherium = helmeted musk-ox, Cervus = elk, Equini = horse, Mammuthus = mammoth, Camelops = camel, Bison = bison, Ovis = big horn sheep, Rangifer = caribou, Antilocapra = pronghorn.

Another study examined the database of 1600 reliable radio-carbon dates of human-occupied sites in South America during the Late Pleistocene. The scientists used 6 different statistical models to estimate the earliest human arrival in South America, and the how rapidly humans colonized the continent. They estimated humans arrived in South America between 16,600 years BP-15,100 years ago, but they lean toward the more recent date. The initial colonizers lived in low population densities and are less visible in the archaeological record. The scientists didn’t use dates earlier than this because the evidence is inconclusive. Both human and megafauna populations increased following the Last Glacial Maximum, but eventually the latter became extinct as humans became more common in the environment. The extinctions seem to correspond to human population densities and not climate change. Grassland environments favorable to megafauna retracted during a Late Pleistocene climate fluctuation, but megafauna began declining 500-1400 years before this, and there was still plenty of grassland habitat available.

A third study, authored by several of the scientists who wrote the study discussed above, compared megafauna populations both spatially and temporarily with the prevalence of fishtail projectile points. Fishtail projectile points were the most common arrowhead used by South American Indians to hunt large mammals. Megafauna populations began to increase about 17,500 years ago when climate following the Last Glacial Maximum improved. (Megafauna population densities were estimated using radio-carbon dates of subfossil remains in the paleobiology database. In my opinion this is a little dubious because the fossil record might not represent actual population densities.) About 13,500 years ago when Indians started using Fishtail projectile points, megafauna populations began to decline. Patagonian grassland and the Pampas hosted the highest populations of megafauna, while the Andes hosted the lowest. Species of megafauna covered in this study included Hippidion (a genus of horses restricted to South America during the Late Pleistocene), horses belonging to the Equus genus, llama, 3 species of ground sloth, glyptodont, notiomastodon, and gompothere. The last 2 were elephant-like species. South America suffered an even larger percentage of large mammal extinctions than North America during the end of the Pleistocene. 82% of South America’s large mammals became extinct compared to 70% of North America’s large mammal extinctions. The authors of this study feel confident humans were primarily responsible because megafauna began declining centuries before any major climate fluctuation, but they did decline when Fishtail point projectiles became more prevalent in the archaeological record.

Fishtail projectile points were used by Paleoindians to kill large mammals. An increase of their appearance in the archaeological record is associated with a decline in megafauna populations.

Chart showing the correlation between the prevalence of Fishtail projectile points and a decline in megafauna populations. From the below referenced study by Prates (2021).

References:

Chatters, J.; B. Pottter, S. Fiedel, J. Morrow

“Mammoth Featured Heavily in Western Clovis Diet”

Science Advances 10 (49) December 2024

www.science.org/doi/10.1126/sciadv.adr3814dr3814

Prates, L.; G. Politis, S. Perez

“Rapid Radiation of Humans in South America after the Last Glacial Maximum: A Radiocarbon-based Study”

PLOS ONE July 2020

https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0236023

Prates, L.; S. Perez

“Late Pleistocene South American Megafauna Extinctions Associated with Rise of Fishtail Points and Human Populations”

Nature Communications 12 (2175) 2021

https://www.nature.com/articles/s41467-021-22506-4

Everglades Mink (Neogale vison evergladensis) Scat Attracts Other Species

The American mink is not endangered and lives all across North America in wetlands with the exception of the American Southwest, but the subspecies that occurs in the Everglades is considered threatened. Mink are weasels well adapted to living in freshwater marshes where they prey upon rabbits, rodents, fish, frogs, tadpoles, birds, turtles, snakes, and insects. They often kill more than they can eat because their primitive brains don’t shut off when the killer instinct is activated. They are relentlessly vicious and sometimes kill animals such as cormorants that are much larger. Put a mink in a cage with a similar-sized rat and the latter will freeze in fear. They’ve escaped into the wild in Europe where they outcompete the native European mink. Mink raised on fur farms are larger than wild mink but have smaller brains and hearts. They don’t make good pets. People handling them usually wear gloves to reduce injuries from bites.

Range of the Everglades mink. Scientists think they have been extirpated from the area around Lake Okeechobee. Mink also live in the salt marshes of the Atlantic and Gulf Coasts.

Mink sometimes capture prey larger than themselves. Scientists think Burmese pythons may be reducing their populations, but mink may be able to kill juvenile pythons. I don’t know what kind of snake this is…maybe an indigo snake.

Florida has abundant freshwater habitats ideal for mink, but they are restricted to 3 areas of the state. They live in salt marshes on the Atlantic and Gulf Coasts, and they occur in the Everglades. Apparently, they’ve been extirpated from the area around Lake Okeechobee. They suffer natural mortality from alligators, coyotes, Burmese pythons, large birds of prey, and outbreaks of canine distemper. In addition marshes have been drained for agricultural use, eliminated much of their habitat. Probably, a combination of these factors caused the disappearance of this subspecies from the Lake Okeechobee area.

Scientists used a golden retriever trained to recognize the scent of spotted skunks, weasels, and mink to locate mink in the Fakahatchee Strand State Preserve and the Picayune Strand State Forest within the Everglades. Mink and weasels can’t spray like skunks, but they smell like them. The dog was rewarded with a toy when he located a mink den. The dog found 1 temporary den used by a female and 2 young. Scientists put up a camera trap where the mink was marking its territory with scat. The trap got some interesting images within the timespan of a week.

Photo of a mink where it was marking its territory with scat. Image from the below referenced study.

Photos of the species attracted to the mink scat. Image also from the below referenced study.

The camera trap captured images of raccoons 24 times, opposums 4 times, fish crows 4 times, and bobcats twice. The camera also recored a gray catbird, a gray squirrel, and a mouse; but these were thought to be incidental, and these 3 species weren’t attracted to the scat.

I’ve never seen a live mink, but I have seen road-killed mink near streams. They are uncommon in the fossil record, probably because they’ve always been relatively less abundant compared to some other species. Nevertheless, fossil evidence does show they occurred in North America since at least the early Pleistocene.

Reference:

Smith, L; and K. Hassler

“Mink Latrines are Hotspots for Wildlife Activity”

Southeastern Naturalist Volume 23 Issure 3 2024

Flawed Study Suggests Anthropogenic Fires Caused the Extirpations of Megafauna Near the La Brea Tar Pits

A group of scientists think they’ve found the answer to what caused the disappearance of most of the megafauna species that lived near the La Brea Tar Pits. They took sediment cores from several sites near the tar pits and measured the quantities and composition of pollen and the amount of charcoal present–an indicator of fire frequency. They radio-carbon dated the layers of the core. They also used radio-carbon dates from 172 specimens of megafauna species in the region including saber-tooth, giant lion, dire wolf, coyote, bison, camel, horse, and ground sloth. They fed this data into a statistical model and concluded as the climate became warmer and drier, the environment became more susceptible to fires set by increasing populations of humans. The anthropogenic fires transformed the landscape from juniper-oak woodlands into a semi-arid chapparal, and the only surviving megafauna species (that they studied) was coyote. (A chapparal is a dry landscape covered in pine, shrub, flowering herbs, grass, and cactus, and the climate consists of mild winters and hot summers.) These extirpations in Southern California occurred about 1,000 years before the extinctions in the rest of the North American continent, but they occurred at the same time these species were in decline elsewhere. Camels and ground sloths disappeared a few hundred years before the other species in this study, but I should note (which this study does not) that the most recently dated specimen was likely not the last surviving member of the species–there still could have been a considerable population that perchance left no fossil evidence. A serious flaw in the conclusion reached by this study occurred to me.

This illustration is a ridiculous exaggeration, and I think it is based on a seriously flawed assumption. From the below referenced study.

List of species used in the below referenced study and their final extirpation date estimates.

The authors of this study assume the transformation of juniper/oak woodlands to a dry chapparal environment resulted in the local extirpations of megafauna here. The problem with this hypothesis is that at least 3 of the species used in this study thrive in semi-arid chapparal like environments. Lions live in semi-arid environments all across Africa. Wild horses are most common in the American southwest where they roam deserts. And camels, of course, are known to live in arid environments, and today introduced wild camels survive in Australian deserts. I realize the North America Pleistocene versions of these species are not exactly the same as modern species, but they were highly adaptable and lived all across North America, and they endured all kinds of sudden dramatic shifts in climate, including peak Ice Ages which caused widespread arid conditions. I seriously doubt a shift to more open drier conditions negatively affected horses, camels, and lions. I think populations of these species would increase in this type of environment.

Horses thrive in the semi-arid type of environment that the below referenced study erroneously assumed caused their extirpation in southern California.

Camels also can endure semi-arid conditions. I think the authors of this study blundered in their conclusion.

19 scientists put their name on this paper. I find it hard to believe this obvious flaw in their conclusion occurred to none of them. It occurred to me before I finished reading the paper. I contacted the lead author of the paper and pointed out this flaw, but so far, he has not responded. It seems as if scientists want to bridge the gap between climate models of extinction with those who hold humans are solely responsible. Put me in the latter camp. The increase in fire frequency is proxy evidence for the presence of humans. Direct hunting by humans increased megafauna mortality above the ability of these large slow-reproducing animals to maintain their populations. It was overhunting by humans, not a change in fire regime that caused the extinction of these species. It is the simplest explanation, and the only one that makes sense to me.

Reference:

O’Keefe, R. et. al.

“Pre-Younger Dryas Megafaunal Extirpations at Rancho La Brea Linked to Fire-Driven Shift”

Science August 17, 2023