Feathered Casanovas

Tall pines dot the mountainside. Hardwood trees leaf out in bursts of vibrant green. Crisp air and peaceful quiet envelop the forest. Suddenly, the silence is broken with high trills in a complex melody of a feathered chorus, a song of romance as dark-eyed junco songbirds seek their perfect partners.

In the hardwood forest, the five- to six-inch juncos, a finch-like bird, nest on the ground or in shrubs close to the ground, seeking dark, moist, cool sites for their homes. The birds typically land somewhere and then run to their nests -- mousing around -- instead of flying directly into the nest. A biologist lurks in the area, setting two kinds of traps to capture them. Steel cages with netting are designed to catch the seed-eating birds humanely to avoid injury, a Wylie Coyote kind of trap. Or the forest may hide mist nets of fine mesh, as invisible as spider webs. Birds can't see them, will fly into the net and be captured, but only for a short time.

After a junco's capture, a biologist carefully administers light anesthesia. Clear, plastic, medical-grade tubing -- similar to an I.V. in a human patient, only a few centimeters in diameter -- is filled with crystalline testosterone. The biologist gently makes a small incision, and using a little tweezers, slips the small tube under the equivalent of the bird's armpit. Surgical glue closes the incision. The testosterone seeps into the bird through the permeable tubing. In this research study, some birds receive small tubes of steroids, while the control group is implanted with empty tubes. All are banded with a small leg ring to track them. The birds are handled fairly quickly and released as soon as possible.

This particular type of junco songbird is an altitudinal migrant -- meaning it migrates up and down the Appalachian Mountains of Virginia, resting in the cool highlands during summer, moving down the mountain in winter. But from spring through summer, the birds' routines resemble speed daters who search for attractive mates. An army of voyeuristic researchers watches and records their activities, how many babies are born to each bird pair, and judges the birds' fitness and their parenting skills.

Researchers record information on breeding for each bird. How much does it weigh? Has it received extra testosterone? How many eggs are laid? How many nestlings do they produce? Do the babies learn to fly? Through binoculars, field researchers note how often birds return to the nest. Other researchers tape-record the birds' songs. Still others conduct DNA paternity tests. In all, the research team monitors more than 400 junco nests for nine breeding seasons.

A long-term testosterone trail

On the mountain, Ellen Ketterson, an internationally known evolutionary biologist specializing in animal behavior, leads the field research. She is a professor at Indiana University Bloomington, and often is cited among the top three researchers in her field in the world. North Dakota State University Assistant Professor Wendy Reed began working with Ketterson as a postdoctoral researcher before coming to NDSU in 2002. It's fitting the field research on romantic lives of juncos occurs at Mountain Lake Biological Station in Virginia, the same location where the popular movie "Dirty Dancing" was filmed. Some of the juncos, research shows, engage in a whole lot of avian dirty dancing.

Although dating and mating practices are unique for many species, there seems to be one constant -- that inexplicable variable called chemistry. Female dark-eyed junco songbirds are drawn to males that sing the sweetest, fly the farthest, strut the sexiest. Their mating ritual is a story of testosterone and estrogen. "One hormone affects a bunch of behaviors," Reed says. "Think about humans. Somebody doped up on testosterone grows big muscles and maybe they're more vocal and aggressive. The same thing with birds. One single hormone affects a whole suite of traits." The hormone in question being the big T -- Testosterone. Research scientists who use it for studies must be licensed to purchase the substance.

The hormone is called into question in everything from the Tour de France to the Olympics. Although banned from sports, some athletes try to get more testosterone into their systems as a way to swim faster, run farther or build muscle. The testosterone in birds is the same type of testosterone found in mammals and humans. While humans may define fitness as washboard abs, in an evolutionary sense, fitness is defined as the ability to reproduce and survive. In biology, the name of the game is getting your genes into the next generation. "It's a combination of being able to survive long enough to do it and then doing it," Reed says. "It" being, well, you know.

Juncos typically form a pair and bond for the season, but don't necessarily mate for life. Call them serial monogamists. Both male and female in the pair provide for their young. "In that sense, they're like a monogamous couple, working really hard to raise their young together," Reed says. "They're the middle class of birds."

On the other hand, the birds pumped full of extra testosterone, it seems, are a bit more adventurous. In the polite vernacular of biology, it's called "extra pair fertilizations." These birds stray from their home nests, cheating on their partners. What makes them stray? Boredom with the same old forest scenery? A mate whose once-endearing qualities no longer hold any charm? Not really. It would appear the extra testosterone creates what some science writers call feathered Casanovas.

Sweet song, but short lived

The extra testosterone makes the males ardent, successful suitors. "In juncos, females are looking for males that are also going to be good parents. Age seems to play a role in this. Older males are typically better able to provide for them than younger males," Reed says. "One thing that testosterone does is increase song rate and song is a way that a male attracts a female." But like a less-than-truthful personal advertisement posted on an online dating service, young male juncos with extra testosterone start singing more and acting like older males. "Females find that to be attractive, so they're kind of fooled into pairing with a high testosterone young male. And young males in the junco world aren't all that good to be paired with. They're bad dads."

Seems the testosterone makes the young males want to fly farther from the nest. "They're good at making babies but not taking care of them," Reed says. The testosterone-laden males don't help at the nest as much and don't help females feed the youngsters as much as males that don't have high testosterone. "Young male juncos can talk the talk but when it comes down to walk the walk, they're not so great."

And while the extra testosterone-treated birds seem to have a good time, the testosterone brings repercussions. The adage "live fast, die young and leave a good looking corpse" applies to the young male juncos. The birds sire more offspring but have a shorter lifespan, because the testosterone boost weakens their immunity and lowers their fat reserves, making them more susceptible to disease. The testosterone also makes them more active, so they become more visible to predators.

Finding the patterns

Nine years of watching the juncos provides valuable data. However, stitching together nine years of data to discover patterns and make scientific conclusions requires something else -- a numbers cruncher who understands biology. Reed happened to know such a colleague. "He's a handy guy to be married to," Reed says of her husband, Mark Clark, an assistant biology professor at NDSU, a population biologist. "I'm a numbers guy. I count things. I crunch numbers," he says with a slight southern accent, stemming from his Tennessee roots.

Clark's math background, quantitative abilities and computer programming experience allowed the researchers to synthesize thousands upon thousands of numbers gathered in nine years of research on the mountain. These streams of data only take on meaning when the puzzle pieces fit together to reveal a complete picture. Imagine assembling a several thousand-piece jigsaw puzzle without a picture on the box to guide you. Ten or 20 years ago, Clark says, the computing costs to analyze the data would have been prohibitive. "We would have been running through that data for a decade or more before we would have gotten to the bottom."

Even with advances in computing technology, between field research, data analysis, and writing the research results for publication in a scientific journal, the entire process took about 13 years of devotion to studying the romantic lives of the dark-eyed juncos.

Attention-getting testosterone

While the subject of testosterone might cause a chuckle, a wink, a nod, maybe even a smirk or a sideways reference to Viagra, the importance of the study is underscored in the attention it's receiving in scientific journals and in the popular press. First published in May 2006 in The American Naturalist, a noted scientific journal, it didn't take long for the study to generate worldwide interest. "Birds gone wild: extra testosterone makes males irresistible" was one headline from LiveScience. The international news agency Reuters and media outlets such as the Washington Post, CNN, MSNBC, CBC and Discover magazine carried stories about the research study.

One scientific reviewer who evaluated the study noted that "Results are novel and provide evidence of trade-offs that have rarely been documented before. This is an important contribution to the field of life history theory."

The University of Chicago Press Journals pointed out that while there have been studies focusing on testosterone levels, mating systems and aggression, there have been few studies that relate testosterone to fitness -- the ability to reproduce and survive. As a writer for Discover noted: "A higher level of the hormone increases sex drive and attractiveness of males, leading to more offspring and increased evolutionary fitness; it also weakens the immune system, amplifies stress, and encourages recklessness, increasing the risk of departing the gene pool altogether."

Results of the study show that male birds with what is considered normal testosterone levels had a 44 percent of surviving to the next year. For the testosterone-charged birds, only 38 percent of them had a similar fate.

"One thing I take away from this study is that with hormones, their effect can be far-reaching," says Professor Mark Clark. "Yes, they may have positive effects in some contexts. But they may come at costs and we don't fully understand that."

Reed, for her part, isn't bothered if the interest in the junco testosterone study is a little on the prurient side. "It's about sex and testosterone," she says. "Science is fun. And a lot of times, the best way to get across complex concepts is with a sense of humor. And of course, everybody wants to think about what this study means for humans."

-- C. Renner