What the Little Birds Tell Us

Bluebirds are valuable for more than symbols of happiness. Their own pursuit of happiness makes them an ideal subject for scientific study. John Swaddle, Robert and Sara Boyd Associate Professor of Biology at William & Mary, is in his third year monitoring bluebirds in and around Williamsburg. He and his students have been monitoring 800 nest boxes throughout the long bluebird mating season. "A lot of birds just breed for the spring and then they're done, whereas bluebirds keep going," Swaddle said. "Some pairs will raise up to three clutches in one year-in other words, three complete broods that will leave the nest. They're a great bird for us to study during the summer because we have different students come in at various times during the summer season, and they can work on slightly different projects."

Indeed, data collected from the birds become part of a number of distinct, yet interrelated studies, such as an evaluation of the development of chicks hatched in different habitats and the mathematical modeling of mingling of individuals among bluebird subpopulations within the greater metapopulation.

The studies have attracted support from the National Science Foundation. The mathematical modeling studies, which also include Dan Cristol from biology and Sebastian Schreiber of the math department, are the focus of a $647,000 NSF grant. This summer, Swaddle and Caitlin Kight, a Ph.D. student at William & Mary, spent lots of time in the field leading a group that also included William & Mary undergraduates and Thomas Nelson Community College students. Swaddle instructed the fledgling researchers in the techniques of weighing, measuring, banding and logging the nestlings. "The baby bird's leg is kind of pudgy, like a human baby," he said, demonstrating how to use a tool to attach a metal band. "It will get skinnier, so don't worry if your band is a trifle snug."

The metal band, stamped with a federally registered number, is supplemented by a set of colored bead bands unique to each bird-for identification, literally, "on the fly." All nestlings are banded, as are whatever adult birds-usually females-caught in the nest box.

A Short Childhood

Bluebirds leave the nest at about two weeks old. Swaddle and his students check on each nest of birds three to four times during their nesting period. Baby birds are removed from the nest, quickly and gently, and placed in a bag. Then each one is weighed. A 35-mm film canister holds the chick still. A caliper is used to measure the wing.

The measurements are used to plot the growth of the chick; the banding not only serves to distinguish nestmates, but also will be used to identify each bird as an adult. Identification of adult birds is necessary to monitor survival rate (the normal is 15-20 percent) and to track the adults. How many return to nest in the old neighborhood, maybe even the same nest box? Do they prefer finding a mate within their own subpopulation? Or, being free as a bird, do they prefer to seek their reproductive fortunes elsewhere?

What's a Metapopulation?

An individual bird's willingness (or reluctance) to look for a mate beyond his or her home flock is what drives the studies of metapopulation dynamics. As urbanization divides natural habitats, animals increasingly live in population groups somewhat separated from each other, but which overlap to varying degrees, creating a "metapopulation."

For example, the bluebirds of the William & Mary campus and those of the Colonial Parkway may constitute separate subpopulations within a larger metapopulation, which also contains other subpopulations. The students observe the degree to which individual birds move among subpopulations, then crunch the numbers to make a mathematical model, using techniques from Schreiber's Math 345 course, Introduction to Mathematical Biology. The quantitative and predictive element of the mathematical modeling gives undergraduates experience in the real world of science. "You can't do science without working in math in some way and NSF are very big in this," Swaddle said. "They realize that there's a big demand in terms of jobs for people who are conversant in both mathematics and biology."

One aspect of interest centers on how much the birds are bothered by human disturbance. Bluebirds are good parents; when they're stressed out, they maintain the necessary level of feeding for the chicks, even at their own expense. When bluebirds start looking for a nesting site, they prefer a bit of woodland adjoining a grassy area. Real estate of this basic description is quite common, but all grassy areas bordering woods are not created equal. Some areas are remote, by human standards, others have constant car and foot traffic nearby.

"All 800 boxes we have are essentially across what you could call a disturbance gradient, starting with places where people never go like the very back fields of some of the Colonial Parkway sites," Swaddle explained. "Nobody goes there except to mow twice a year so those are completely undisturbed areas. At the other end of the gradient we have areas on golf courses and on campus where there are people around all the time and places where there are cars driving past. Although it sounds obvious that disturbance should affect the birds' breeding success and population fitness, it's actually not been studied in any quantitative way."

In summer of 2004, Swaddle's team collected data on some 2,000 individual bluebirds. He hoped to increase that number during 2005. He intends to keep the studies going for another three or four years. The study has generated a number of interesting, if preliminary insights. For instance, Swaddle said he was surprised by the rate at which he's seen birds return to the same nest box. Another surprise comes from comparing the reproduction of bluebirds nesting on immaculately groomed golf course fairways with those in semi-managed areas such as the Colonial Parkway and state parks. The golf course birds, so far, have been producing more offspring, but the chicks seem to be scrawnier.

As the summer passed, some of the students began analyzing the grubs and bugs the insectivorous bluebirds feed their young to see if there's something lacking in the food-or perhaps just a case of more mouths to feed among the fairway bluebirds.

"The temptation with this type of work is to stop short once you have something interesting, but really to understand any of the situations we're investigating, you need a long-term study," he said.

Good Science, Great Education

The bluebird studies are a perfect combination of good science and a great out-of-the-classroom experience.

People certainly love bluebirds and encourage them to move into the neighborhood by putting up nest boxes. While these studies will contribute to our understanding of how best to co-exist with this attractive species and other wildlife, the educational aspects are equally valuable.

The bluebird projects contain enough science to challenge a Ph.D. student and, at another level, to serve as an ideal introduction to field biology and quantitative techniques for fledgling biologists. The work also serves as an excellent link to science-oriented students at Thomas Nelson Community College. In fact, at least one TNCC bluebirder, Rachel Biondolillo, has already transferred to William & Mary.