Winter's Tale: From birds to snow angels, traces tell a story

Written in snow: While most people are focused on Atlanta's human traffic jam, Tony Martin is using his camera to record animal traffic patterns. 

By Carol Clark

For Emory ichnologist Anthony Martin, a snow day is a great day to do science in the field. Ichnology is the study of traces left by living things, including tracks, and Martin is an expert in the traces of both prehistoric animals and modern-day ones.

Photo of Martin by Ruth Schowalter.

“Living in Georgia, it’s rare for me to see tracks in snow, so it’s a big treat,” Martin says. “It’s been really fun to see the patterns left by birds around our feeder, right outside our front door.”

Martin doesn't have to see the birds to know that the feeder was visited by hopping, skipping warblers, sparrows and wrens.

A blanket of snow to Martin is like a big sheet of white paper with all kinds of stories written on it.

If you take a walk in the snow, you may be surprised by the variety of animals and their activities recorded in it. Martin advises amateur ichnologists to start by looking for patterns.

“Try to think about what sort of story is being written in the snow by the animal,” he says. “Focus on ‘what is this character doing, rather than ‘who is this character.’ That makes for some really fun tracking.”

A snow angel resting trace, seen in Decatur's Adair Park. Photo by Tony Martin.

Related:
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Polar dinosaur tracks open new trail to past

Burrow into a good book on wildlife traces

When scientists go to the movies, they need their space

Keir Dullea played astronaut David Bowman in "2001: A Space Odyssey."

“We can’t count on science fiction to always get the science right,” Emory physicist Sidney Perkowitz told Popular Mechanics. “But we can count on it to generate excitement and interest in viewers.” 

Ocasionally, however, Hollywood does get it right. Popular Mechanics polled dozens of scientists and engineers on their favorite sci-fi movies, based on both scientific plausibility and cinematic merit.

Their top pick: “2001: A Space Odyssey,” the 1968 film of space exploration by director Stanley Kubrick. Even seasoned astronauts gave Kubrick the thumbs up for his depictions of space flight.

Click here to read the other 10 top sci-fi movies named by the scientists and engineers.

The magazine also polled the scientists about the worst sci-fi movies. Among the top five is 2003’s “The Core” which, Perkowitz says, “gets more science wrong than almost any other film I know.”

Related:
Fantastic light: From science-fiction to fact

Psychologists document the age our earliest memories fade

What's your earliest surviving memory? 

By Carol Clark

Although infants use their memories to learn new information, few adults can remember events in their lives that happened prior to the age of three. Psychologists at Emory University have now documented that age seven is when these earliest memories tend to fade into oblivion, a phenomenon known as “childhood amnesia.”

The journal Memory published the research, which involved interviewing children about past events in their lives, starting at age three. Different subsets of the group of children were then tested for recall of these events at ages five, six, seven, eight and nine.

“Our study is the first empirical demonstration of the onset of childhood amnesia,” says Emory psychologist Patricia Bauer, who led the study. “We actually recorded the memories of children, and then we followed them into the future to track when they forgot these memories.” 

The study’s co-author is Marina Larkina, a manager of research projects for Emory’s Department of Psychology.

The Bauer Memory Development Lab focuses on how episodic, or autobiographical memory, changes through childhood and early adulthood.

“Knowing how autobiographical memory develops is critically important to understanding ourselves as psychic beings,” Bauer says. “Remembering yourself in the past is how you know who you are today.”
 

Scientists have long known, based on interviews with adults, that most people’s earliest memories only go back to about age 3. Sigmund Freud coined the term “childhood amnesia” to describe this loss of memory from the infant years. Using his psychoanalytic theory, Freud made the controversial proposal that people were repressing their earliest memories due to their inappropriate sexual nature.

In recent years, however, growing evidence indicates that, while infants use memory to learn language and make sense of the world around them, they do not yet have the sophisticated neural architecture needed to form and hold onto more complex forms of memory.

Instead of relying on interviews with adults, as previous studies of childhood amnesia have done, the Emory researchers wanted to document early autobiographical memory formation, as well as the age of forgetting these memories.

The experiment began by recording 83 children at the age of three, while their mothers or fathers asked them about six events that the children had experienced in recent months, such as a trip to the zoo or a birthday party.

“We asked the parents to speak as they normally would to their children,” Bauer says.

She gives a hypothetical example: “The mother might ask, ‘Remember when we went to Chuck E. Cheese’s for your birthday party?’ She might add, ‘You had pizza, didn’t you?’”

The child might start recounting details of the Chuck E. Cheese experience or divert the conversation by saying something like, “Zoo!”

Some mothers might keep asking about the pizza, while another mother might say, “Okay, we went to the zoo, too. Tell me about that.”

Parents who followed a child’s lead in these conversations tended to elicit richer memories from their three-year-olds, Bauer says. “This approach also related to the children having a better memory of the event at a later age.”

Memories that stick around longer may have richer details associated with them.

After recording these base memories, the researchers followed up with the children years later, asking them to recall the events that they recounted at age three. The study subjects were divided into five different groups, and each group of children returned only once to participate in the experiment, from the ages of five to nine.

While the children between the ages of five and seven could recall 63 to 72 percent of the events, the children who were eight and nine years old remembered only about 35 percent of the events.

“One surprising finding was that, although the five-and-six year-old children remembered a higher percentage of the events, their narratives of these events were less complete,” Bauer says. “The older children remembered fewer events, but the ones they remembered had more detail.”

Some reasons for this difference may be that memories that stick around longer may have richer detail associated with them and increasing language skills enable an older child to better elaborate the memory, further cementing it in their minds, Bauer says.

Young children tend to forget events more rapidly than adults do because they lack the strong neural processes required to bring together all the pieces of information that go into a complex autobiographical memory, she explains. “You have to learn to use a calendar and understand the days of the week and the seasons. You need to encode information about the physical location of the event. And you need development of a sense of self, an understanding that your perspective is different from that of someone else.”

She uses an analogy of pasta draining in a colander to explain the difference between early childhood and adult memories.

“Memories are like orzo,” she says, referring to the rice-grained-sized pasta, “little bits and pieces of neural encoding.”

Young children’s brains are like colanders with large holes trying to retain these little pieces of memory. “As the water rushes out, so do many of the grains of orzo,” Bauer says. “Adults, however, use a fine net instead of a colander for a screen.”

Now that Bauer has documented the onset of childhood amnesia, she hopes to hone in on the age that people acquire an adult memory system, which she believes is between the age of nine and the college years.

“We’d like to know more about when we trade in our colanders for a net,” she says. “Between the ages of 9 and 18 is largely a no-man’s land of our knowledge of how memory forms.”

Images: iStockphoto.com

Related:
How our earliest memories gel
What is your baby thinking?
Stories your parents should have told you

Big brain theories of evolution

More than two million years ago, the Earthlings with the biggest brains were dolphins, and certain whales, writes Robert Krulwich on his NPR blog Krulwich Wonders. Below is an excerpt from the post, which explores how the sizes of brains change during the course of evolution:

"Lori Marino, at Emory University in Atlanta, has been studying fossilized brains. And looking back, she sees sudden spurts of brain growth in different animals.

'"[T]he most dramatic increase in brain-to-body ratio in dolphins and toothed whales occurred 35 million years ago,' she tells Chris Impey, the astronomer and writer, in his book Talking About Life. Something happened to make their medium-sized brains bigger, Lori says, then bigger still. For 20 million years certain dolphin species kept their brains growing until — just as mysteriously as it started — about 15 million years ago, they stopped.

"Why? Had the dolphins answered some secret dolphin question? Figured out a puzzle? Adapted to an environmental change? Gotten tired? Hit a limit? What?

'"That's the $6 million question,' Lori tells Chris.

"We don't know. We do know, however, that dolphins aren't the only ones. The same thing happened to us."

Click here to read the whole Krulwich Wonders post.

Related:
Do dolphins deserve special status?
Hominid skull hints at later brain evolution

Photo by NASA

Wild sparrow study traces social behaviors in the field to specific gene

The white-throated sparrow is considered a good model organism for the genetic basis of behavior. (Photo by Cephas/Wikipedia.)

By Carol Clark

A unique study of the white-throated sparrow has identified a biological pathway connecting variation in the birds’ aggression and parenting behaviors in the wild to variation in their genome. 

The Proceedings of the National Academy of Sciences (PNAS) is publishing the results of the experiments, conducted by the lab of neuroscientist Donna Maney in Emory’s Department of Psychology.

The research, which comprised behavioral observations of the study subjects in the field and laboratory analyses of their gene expression in the brain, showed that variation in the expression of the estrogen receptor alpha (ER-alpha) gene strongly predicts the birds’ behavior.

“We believe this is the most comprehensive study yet of how the rearrangement of a chromosome affects social behavior in a vertebrate,” says Brent Horton, a post-doctoral fellow in the Maney lab and lead author of the study. “So much of the process of genetic discovery is restricted behind closed doors in a laboratory. But our study began in the woods, where we first observed the social behaviors of the actual subjects of our experiments in their natural setting. The results provide valuable insight into the mechanistic basis of aggression and parenting in all vertebrates, including humans.”

Such integrated studies “are exceedingly rare,” Horton adds, “because they require such a variety of resources, expertise and well-balanced collaboration.”

In addition to Horton and Maney, the principal investigators included Eric Ortlund, a biochemist and an expert in the ER-alpha gene at the Emory School of Medicine; and James Thomas, a human geneticist who was formerly with Emory and now works at the National Institutes of Health. Co-authors include William Hudson, a graduate fellow in Ortland’s lab; Wendy Zinzow-Kramer, a post-doc in the Maney lab; Sandra Shirk, a research associate; and Emily Young, an undergraduate student of biology at Georgia Tech.

The white-striped morph of the white-throated sparrow, left, and the tan-striped morph, right. The two morphs and the resulting color difference occur in both sexes. Photos by Brent Horton.

The white-throated sparrow is considered a good model organism for the genetic basis of behavior due to a genetic event that has divided the species into two distinct forms that differ in their behavior. These two forms, the white-striped morph and the tan-striped morph, are easily distinguished by their plumage markings.

At some point during the evolution of the species, a chromosome broke and flipped. This process, called an inversion, rearranged the sequence of the chromosome.

The white-striped birds, which all possess at least one copy of the rearranged chromosome, tend to be more aggressive and less parental than the tan-striped birds, which do not have the rearranged chromosome.

“The two morphs work beautifully in evolution because one color morph almost always mates with the opposite color morph,” Horton says. “They complement each other.”

For the past decade, the Maney lab has been a leader in documenting the neuroendocrine and genetic differences between the white-throated sparrow morphs. For the current study, funded by the National Institutes of Health, Maney recruited Horton, a field biologist and an expert in the natural history of the white-throated sparrow.

“At heart, I’m a behavioral ecologist,” Horton says. “I want to integrate neuroscience and genetics into my work to understand the behaviors that I see in the wild.”

The scientists knew that the different behaviors of the two sparrow morphs were linked to the chromosome inversion. “We wanted to know what genes captured by that chromosome also differ between the morphs, in order to identify the genetic mechanisms that may explain the behavioral differences,” Horton says.

The white-throated sparrow winters in the South, but mates and raises its young during spring and summer in the North. “In a sense, I migrated with these birds,” Horton says, explaining how he conducted fieldwork over three years. Each summer, he packed up his family and left Atlanta for Argyle, Maine, to tag birds for the study and spend weeks observing their behaviors in a forest. 

White-throated sparrows nest on the ground under shrubs or low in trees. They are one of the most common birds seen in the forest and at suburban bird feeders. Their distinctive song is often likened to the phrase, “Old Sam Peabody … Peabody.” Click here to listen to a recording of the song.

Watch a field video of a pair of white-throated sparrows feeding their young, made by Brent Horton.

To measure parental behaviors in the birds, Horton recorded the number of feeding trips they made for their young during a specified time. To measure aggression, he recorded their song rate in response to a simulated territorial intrusion: A live sparrow in a cage was displayed in the breeding territory of the wild study subjects, accompanied by the broadcast of a male song.

“The song of the birds is a form of aggression,” Horton explains. “They’re saying ‘get out of my territory.’ The rate at which they sing gives a measure of their level of aggression.”

The field observations were followed by laboratory analyses of the study subjects, to hone in on differences in their neuroendocrine gene expression. The researchers focused on ER-alpha as a primary candidate, since it is one of the genes captured by the chromosome inversion and had been previously linked to social behaviors in vertebrates.

Their analyses documented how the genetic differentiation between the morphs affects the transcription of ER-alpha. In one brain region thought to be important for aggression, white-striped birds had three times the level of ER-alpha than did the tan-striped birds. By looking at both the behavioral data and the lab data together, the researchers found the expression of ER-alpha in that region and others predicted variation in territorial aggression and parenting.

“The behaviors that differ between the morphs are known to rely on sex steroid hormones such as testosterone,” Maney says. “But we already showed in 2009 that even when their testosterone levels are equal, the white-striped males still sing more than the tan-striped males. This finding led us to suspect that brain sensitivity to hormones differs between the morphs. ER-alpha has a hormone receptor that makes the brain sensitive to testosterone, so it makes sense that the white-striped birds have higher levels.”

The researchers hypothesize that the mechanism they have identified may have played a major role in behavioral evolution.

“Humans also show variation in aggression and parenting,” Horton says, “but we know little about what contributes to this variation and how our behavior can in turn affect our brains. This bird gives us important clues about what to look for as we try to understand the complex interplay between genes, proteins and our own social behaviors.”

The ER-alpha findings conclude the first phase of the work. The research team is also investigating a suite of other neuroendocrine genes captured by the chromosome rearrangement that are thought to be important players in the regulation of social behavior.

Related:
Birdsong study pecks theory that music is uniquely human
Doing the math for how songbirds learn to sing

Look, up in the sky: It's a sun dog!

The "mock sun," or sun dog, can be seen to the left of the actual sun. Photo by Woody Hickcox.

Even on an icy, cold day, when many people are just focused on trying to stay warm, Woody Hickcox takes the time to scan the outdoors and look for gems of natural beauty. That’s why he noticed the sun dog hovering amid the cirrus clouds over the Emory campus last Tuesday around 4 pm. He snapped the above photo from the 5th-floor patio of the Math and Science Center.

“They’re fairly common, if you keep your eyes out for them,” says Hickcox, a senior lecturer in Environmental Studies.

Sun dogs are atmospheric phenomenon caused by the refraction of light from hexagonal ice crystals, called diamond dust, that drift in the air at low levels. They may appear as a colored patch of light on one side of the sun, and can also include a luminous halo or arc.

"Back in the day, sun dogs were considered omens, like comets," says Hickcox. The above photo was taken at Stonehenge by Tim Daw (via Wikipedia Commons).

Here’s a link to a fuller explanation of sun dogs (known as parhelia to meteo-nerds).

Hickcox says his favorite sun-dog sighting occurred in the early 1980s, as he was driving with his family across Alabama. “It was one of those days when the sky was lit up with just about every optical phenomenon,” he recalls. “There were really good examples of sun dogs, halos and parhelic arcs. We pulled to the side of the road and just looked at the sky.”

Hickcox has taught meteorology at Emory for more than 30 years and next fall will teach a class on climate change. He invites those who are interested in the sky and optical phenomenon to drop by the department and look through some of the books he has collected on the topic, including striking photographs.

“The day-time sky is full of amazing and weird sights, not just sun dogs,” Hickcox says. “You just have to know what to look for and when.”