Safran and her team, which included dozens of CU-Boulder students and volunteers from the community, trapped scores of barn swallows with mist nets in rural sites around Boulder County, measuring and weighing them and taking blood and feather samples before releasing them back into the wild. Each bird was sampled between two and four times over the breeding season. The blood analysis tests took place in McGraw's Arizona State University lab.
The three carotenoids measured in the study -- leutin, zeaxanthin and beta cryptozanthin -- all are antioxidants that are sold in health food stores around the world. The swallows obtain carotenoids from insects that feed on plants rich in the nutrients.
Since the barn swallow reproductive season lasts about four months, it makes sense that individuals should be able to signal their abilities as parents and mates over time, rather than at the beginning of the season when pair formation takes place, she said. "The swallows that maintained high levels of carotenoids throughout the summer got more reproductive attempts and produced more offspring," Safran said.
Many of the high-quality barn swallow pairs, which weighed more than their peers during the breeding season, produced two clutches of eggs rather than one, producing a greater number of young that fledged, she said.
"Nutritional status is a 24-hour game, because many nutrients don't carry over beyond the next day," she said. The "top" barn swallows appear to be very efficient at foraging and dealing with the costs of reproductive success on a day-b
|Contact: Rebecca Safran|
University of Colorado at Boulder