University of Georgia (UGA) Ph.D. candidate Erin Ulrey and a team of researchers sprinkled cracked corn over an open field at the Savannah River Site in Aiken, S.C., where they waited for wild turkeys to emerge from the hardwood forest.
"Some days, you may get lucky," said Ulrey. "Some days, you might not see any."
But food is scarce in the winter, and the turkeys are hungry. Once an unsuspecting flock waddled into their trap, the team fired a few rockets into the air, trapping about seven turkeys in a weighted net about the size of a backyard swimming pool.
Quickly, they isolated each bird into a turkey-tailored cardboard box, and slipped child-sized socks over their heads to prevent cries of distress that could set off a flock-wide panic. Dodging the sickled spurs jutting from the males' heels, the team banded their left legs and strapped backpacks -- a paracord-like rope tied to a GPS -- onto their wings. An antenna sticks out of each radio-turkey, which can carry them around for up to a couple of years, Ulrey observed.
UGA and Louisiana State University (LSU) researchers began GPS-tracking wild turkeys about 15 years ago, when they noticed a two-decade decline across Southeast and Midwest populations, said UGA National Wild Turkey Federation Distinguished Professor Michael Chamberlain. Much of the decline is driven by habitat loss, especially of hardwood forests providing seeds and acorns crucial in winter. It's "a double hit," as Chamberlain put it.
Despite their penchant for blocking roads, wild turkeys are elusive. Brown and grey feathers blend into forest foliage; a 340-degree field of vision alerts them of predators. They can even see colors on the UV spectrum, invisible to the human eye. Researchers don't know how many wild turkeys there are in Georgia and in the country, Chamberlain said. Instead, they study other measures to assess population health, such as genetic diversity. The greater the diversity, the more resilient a population is to disaster, disease and other disturbances.
Over the past few years, Ulrey along with UGA and LSU researchers have been gathering genetic data, capturing hundreds of wild turkeys across Georgia, South Carolina and Louisiana. But instead of extracting just blood samples as the labs had usually done, they followed hens to their nests and collected egg membranes, inspired by the work of other avian-minded colleagues.
And they discovered something unexpected.
In three sites where turkeys are hunted, it appeared that females were more likely to produce other females. That was not the case at the Savannah River Site, where hunting is prohibited. While Ulrey and Chamberlain offer some possible explanations, "we need to continue the work," said Chamberlain. "There could be multiple things that are interacting to cause observations in the natural world."
The talking toms
In turkey world, male and female interactions are pretty much business-only. They flock apart for most of their lives, then come together during the spring to breed, featuring courting males' diva-like displays of gobbling, strutting and wing-dragging. As soon as a day later, hens lay their eggs, about a dozen per clutch.
Despite the hens' patient squatting and sitting for about 28 days, just about a third of their nests are successful, said Ulrey. The rest can be lost to predation, flooding or just pure probability.
Meanwhile, the turkey toms (males) have ventured off into posses. They embark on their own tests, or flappy chest-puffing, beak-poking fights with one another. In their pecking order, the strongest toms get to reproduce with the most hens. Over half of females, on the other hand, mate with just one male, Ulrey's study showed.
Because of this mating system, Ulrey hypothesized hens would hatch more males. Toms can spread their seed more widely, and also their mother's genetics. Adult avian males also tend to exhibit higher survival rates, as nesting takes more energy and leaves stationary mothers at greater risk of predation. So, more male offspring would be evolutionarily advantageous for the mother in the long run, Ulrey and other researchers surmised.
In the field, researchers thought they could already be witnessing this phenomenon. Winter traps caught few juvenile turkeys, a "perplexing" potential sign of low population productivity, said Chamberlain. But when researchers did catch a juvenile, they tended to be male.
"Our thinking was, maybe they're just hatching more males," said Chamberlain.
It's (more likely) a girl!
After winter trapping in the spring and summer, Ulrey and her team at the Savannah River Site tracked the hens to their nests in the upland pines, which provide wooded protection from predators and an understory of insects and seeds she can forage without traveling too far from her nest. In all four locations across the three states, researchers sampled over 700 egg membranes, the papery film between shell and egg that protects the embryo.
It was a scramble to get to the eggs that cooked in summer temperatures reaching the mid-90s, Ulrey recalled. Researchers monitored them daily, racing against a 24-hour clock after every egg's hatching. High heat and humidity could degrade the DNA samples past that point.
Once Ulrey analyzed the trove of DNA she helped collect for three years, she noticed a difference between the offspring at the Savannah River Site and the other study areas.
"We were simply trying to study sex ratios, and in doing so, we found this really interesting result," said Chamberlain.
The chance of producing male offspring at the hunted sites was 47% lower than at the Savannah River Site, where hunting is prohibited.
This bias for female offspring suggests two possible explanations.
One is that stressed-out hens on hunted sites might be producing more maternal glucocorticoid hormones that are deposited into the egg yolk and impact offspring development, including the sex.
Another possibility is that males are hunted more than females.
In the spring hunting season, males are often the first to go, Ulrey said. Flamboyant, large, sporting iridescent red, white, and bluish feathers, and attracted to the gobbles a hunter might reproduce with devices, they make for an easier target than their smaller, shier female counterparts.
And Ulrey's results reflect that trend. Adult female survival on the hunted sites proved to be higher.
As for the male advantage researchers initially predicted, it could be irrelevant in spring hunting sites. Many males were likely killed before they bred. Therefore, the evolutionary benefits of passing on their mothers' genes could have been nixed, Ulrey said.
So, hens may be adapting by producing more female offspring with higher survival in spring-hunted areas. In humans, males with XY chromosomes determine the sex of the child. But in avian species including turkeys, females determine the sex.
More questions than answers
Still, the findings have left researchers puzzled. Why did they catch fewer juvenile females in the winter, but find more female hatchings in the spring and summer?
"We're losing these young females," said Chamberlain. "It's not something that can be easily explained."
Part of getting to the answer is figuring out whether the driving force behind female-biased offspring is indeed hunting pressure, Chamberlain added. More non-hunted sites will have to be tested beyond the Savannah River Site.
"We are now seeking routes to conduct research on other non-hunted populations. As you can imagine, it's not easy to find," said Chamberlain. "It's [also] just trying to get the resources, to do that work."
That's work including yet more cycles of winter trapping, spring tracking and summer number-crunching all over again.
Jillian Magtoto covers climate change and the environment in coastal Georgia. You can reach her at jmagtoto@usatodayco.com.
This reporting content is supported by a partnership with Green South Foundation, Prentice Foundation and Journalism Funding Partners.