(female narrator) Day breaks over the lush forest of Mountain Lake, Virginia.
A male dark-eyed junco is up at dawn singing defiantly. His song signals the ownership of territory.
The days are getting longer as the month of May rolls along. Breeding season is in full swing.
The stakes are high. Males must defend a territory and attract a mate in order to get a chance at reproducing. Breeding pairs must compete for food, not only to feed themselves, but also to nourish their offspring.
There will be winners and losers each year. Some pairs will produce up to 15 young, while most will fail altogether.
Males must balance the conflicting demands of survival versus reproduction and the urge to court additional mates versus caring for their own young.
Understanding how such choices are determined has perplexed biologists for a long time.
For researchers who study evolution and behavior at the nearby Mountain Lake Biological Station, the breeding season is also a busy time, and morning is a critical part of the day.
(female) Like most field biologists, I take a lot of pleasure in being alone in the field.
Mountain Lake is often misty and cool in the morning with the leaves dripping, and the forest feels close and dark.
Morning is also a great time to discover what the birds are doing, learn their secrets, and see them on their own terms.
My name is Ellen Ketterson, and I'm a professor of biology at Indiana University. I've been studying the junco for a very long time.
I've been conducting research at Mountain Lake Biological Station for nearly 30 years. I first came in 1979 with my husband, Val Nolan. We found this was a truly fantastic place to do research. The bird we were and still are interested in, the junco, is very abundant here.
(narrator) Juncos are simple, elegant little birds. You can recognize them by their pale underbellies and white tail feathers, which they flash when they fly.
The junco is often called the snowbird, a name likely given to them in the eastern United States, where they arrive in autumn and stay through winter, only to migrate away in the spring.
(Ketterson) Juncos are like people. One reason for studying birds and not studying mammals, most mammals, is that birds form pair bonds, just as people form couples. And when birds take care of their offspring, usually the male helps.
I've studied the Junco for so long, in part, because it's so amenable to study.
It lets you study it. Juncos live on the ground. It's possible to study them without climbing trees. They build nests on the ground, so you can find them.
They thrive in captivity, so you can provide them with seeds or put them in different social configurations, and they're content. They actually reveal their biology to you.
We study them in naturalistic settings in our aviaries at Indiana University, where we can provide large cages and let the birds live almost naturally, as they would in the field.
In the aviary, you can manipulate diet, you can manipulate sex ratio. You can look at the birds at different seasons and learn things easier than in the field.
And just like Rowan, nearly a century ago, we can manipulate daylight.
But the core focus of the research is the field work, what we learn by studying the birds in their natural habitat.
Here's a nest about six feet up in this root mass. And it's not active, but it's a complete nest from earlier this season. In a downpour, that nest and the sitting female should stay dry. Females will look for a natural cavity or a place that has roots or grass or something on top that will keep it dry.
If rain blew in, it could get wet. But the female would protect the babies from a hard rain. But it's at least mostly protected from the rain. Some nests are amazing. It could rain for days and they're just bone dry.
It may be surprising to some people that we can walk in the woods and look at birds and understand something about science. There's nothing really, at first glance, unusual about the junco. It's just a little gray bird and it's everywhere.
(male) It's usually about seven or eight people of various ages and backgrounds-- people all interested in the same thing. We're all interdependent, in that we all need to have certain things accomplished.
We all often depend on having nests found, so that's a collective effort. That's a big and most enjoyable part of the job. So for 15 summers, I've spent almost every day in the woods looking for these nests. I, somehow, never get really tired of it.
(male #2) Natural selection has done a good job of making sure that their nests are hidden. You have to work really hard to outwit them.
(male #1) You might slump two days where you don't find anything. Suddenly a bird flushes up from a place you didn't expect a nest after looking at the obvious places. That's a true joy that I always come back with. You return saying, "I found the nest. No one else could find it." There's competition about who's the best nest finder.
(narrator) Locating nests is important because it allows monitoring of breeding pairs and the offspring they produce each season. Another major job every summer is to keep every bird in the population banded with a unique set of leg bands. The first time each bird is captured, either as an adult or as a nestling, lightweight aluminum and colored plastic bands are wrapped around their legs.
So when they're spotted in the field, even a quick look through binoculars, it's possible to tell who's who.
This bird has a silver over a red band on his left leg... and a light blue on his right. He is known as Light Blue, Silver Over Red.
To capture adult birds, researchers bring lightweight nylon nets, called mist nets, into the field, which are set up between two poles staked securely into the ground.
Good mist nets set up in shade or before a dark background so that it appears invisible to the birds. Seed bait and a playback of a junco's territorial song are commonly used to lure them into the nets.
When juncos hit, they are caught out of midair, but are not harmed.
Researchers are trained to remove them promptly and safely.
Once in hand, a wide variety of data are collected in a few minutes. Measurements like wing, tail, and bill length and body mass are recorded.
Birds are screened for external parasites, such as mites or lice. Photos are taken to quantify the size or color of social batches, like the amount of white in the tail.
Perhaps most importantly, just a few drops of blood are collected from a vein in the wing. The bird is released back into nature,
but the small blood sample will go the lab to provide a wealth of information for years to come.
From just a tiny drop of blood, researchers can measure genetics, immune function, and nutritional state
and screen for diseases, such as avian malaria.
The blood also allows scientists to measure levels of hormones that regulate reproduction and sexual behavior. Among these hormones is testosterone. Most people know of testosterone as the male hormone that's related to muscle mass, aggression, and sexual behavior. But testosterone also modulates a whole host of other behavioral and physiological functions in both males and females. This knowledge is taken for granted. But as recently as the late 1980s, much less was known about the importance of hormones in natural populations. For over a decade, the Ketterson and Nolan Lab conducted a ground-breaking field experiment which shed light on testosterone's complex effects.
(Ketterson) Two traits that we've been interested in are mating behavior and parental behavior. Lots of people have been studying polygenous birds or polyandrous birds, where multiple females mate with one male or multiple males mate with one female. But most birds mate monogamously-- about 90% of bird species. We wanted to know why that was. The best way to pursue a question like that is to alter the birds so that they exhibit different parental behavior or different mating systems. Then ask whether their reproductive success or their survival is the same. Is it better to be the way they are or would they be in some alternative configuration? It's an experimental approach to the evolution of life histories.
(narrator) Ketterson and Nolan designed an experiment utilizing testosterone to alter the biology of male juncos. Two groups were implanted with capsules under the skin throughout the breeding season each year. The experimental males got capsules that secreted testosterone, resulting in elevated levels. While the control birds received empty capsules. Over the course of 13 years, researchers documented how the increased testosterone altered the social behavior, physiology, reproductive success, and survival of both groups. They attached radio transmitters to the birds' backs in order to monitor movement and mapped the size of the territory each male defended. They also recorded how often each male sang his territorial song. On average, testosterone-implanted males defended larger territories and sang territorial songs more often when compared to controls. The larger territories and more frequent singing both indicated that the males with high testosterone levels were investing more effort into attracting and retaining mates. But would these behavioral changes lead to greater mating success or a higher reproductive output? Juncos are socially monogamous, with one male and one female defending a territory and caring for one nest at a time. But juncos are also sometimes unfaithful to their partners, mating and siring offspring outside their social pair bonds. This makes it necessary to use DNA fingerprinting to determine the biological father of each nestling. Using methods similar to a human paternity test, DNA samples were collected from all the adults and nestlings hatched during the study. And genetic markers were used to assign parentage. All of the males in the study, whether they had testosterone implants or not, behaved as if they were monogamous, attracting a single female mate with whom they defended a territory and built a nest.
But the paternity tests revealed that testosterone-treated males were much more likely to mate with neighboring females outside their social pair bond. Control males, on the other hand, were more likely to remain monogamous, even if their partners were not. This meant that eggs fertilized by testosterone-treated males often ended up in the control males' home nests and that control males cared for nestlings not their kin. On average, the high-testosterone males mated with more females than control males did. And these additional mates led to a greater total number of nestlings produced by the high-testosterone males. It's seen that having higher testosterone is beneficial, conferring higher fitness, in terms of the numbers of offspring produced or the number of mates that a male attracts. That's only half the equation. The quality of the offspring matters. And it also matters whether the male survives to reproduce again in each subsequent season.
(narrator) Offspring quality is influenced by the amount of parental care that nestlings receive. This behavior was measured by recording the number of feeding trips parents made to the nest hourly. In addition, nestlings were weighed and growth rates were calculated. Control males fed their young much more frequently, nearly twice as often as the high-testosterone males, indicating that the elevated testosterone was suppressing male parental care. As a result, nestlings with high-testosterone fathers grew more slowly, making them less likely to survive into adulthood. The final piece of the puzzle was examining the impact of the experimentally-increased testosterone on survival.
(Ketterson) When we censused the population each year, we found that the males treated with testosterone were less likely to return. Their annual rate of survival was about half that of the control males. What we thought we were seeing was the cumulative effect of a lot of small changes in behavior and physiology that made life just slightly more perilous for a male treated with testosterone. If it's how many mates you acquire or how many offspring you produce, then males benefit from having higher levels of testosterone. If it's the quality of the offspring he produces or how long he lives, then it's more beneficial for a male to have lower testosterone. What our study showed is that it's possible to take all those components of fitness and put them together and calculate a net lifetime reproductive success.
(narrator) The testosterone studies are just one of many diverse topics explored by the Ketterson and Nolan Research Group. Since 1976, the lab has published over 150 articles across a range of scientific journals. All from studies of the dark-eyed junco.
(Ketterson) We've studied a lot of different topics in juncos. We've studied migration, disease ecology, immune function, mating systems. One of the things I've learned is, while the bird may have remained the same, the questions were always changing. There's a lot to be gained by studying a single bird over a long period of time. Because the bird leads you to places you never expected.
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