For Immediate Release
The house sparrow is a highly invasive pest in North Carolina, and bluebird enthusiasts frequently throw their eggs out and remove their nests to keep them from overtaking the nestboxes that bluebirds call home. A new study puts those discarded eggs to use in detecting heavy metal contaminants in bluebird habitats, which often border human communities.
To collect the eggs, researchers reached out to bluebird watchers through Sparrow Swap, a cooperative program between North Carolina State University and the N.C. Museum of Natural Sciences that provided volunteers with equipment to store and send in house sparrow eggs. The program allowed researchers to obtain valuable information from eggs that would otherwise be destroyed and discarded.
“House sparrows are not protected by the Migratory Bird Treaty Act, and so we knew that tossing eggs was a practice that people are already doing,” said Sparrow Swap creator Caren Cooper, professor of forestry and environmental resources at NC State and co-author of a paper on the study. “We wanted to make the best of that situation and make sure these eggs were not being terminated in vain.”
The main challenge in obtaining the eggs was to build a suitable way for birdwatchers to send them without breaking. Researchers used a packaging container that was particularly apt for the job – plastic Easter eggs.
“We mimicked the way that a lot of electronics are shipped, where they’re placed inside a solid casing and squished between softer materials that keep them from moving,” Cooper said. “We had the participants put the eggs into plastic Easter eggs with the addition of a firm kind of plastic wrap which immobilized the eggs, suspending them in the middle of the Easter eggs. Then volunteers could put several of the Easter eggs into an egg carton and send it to us with everything intact.”
Researchers aimed to determine if the coloration of house sparrow eggshells could indicate the presence of heavy metal contamination in bluebird habitats, which often overlap with human spaces like backyards and public recreation areas. Egg coloration alone did not correspond to the level of heavy metals in the eggshell, Cooper said, which means egg color in this case is not a useful bioindicator.
“While we did not find a strong enough connection between eggshell pigmentation and the presence of heavy metals to use coloration as an indicator, our study was informative because we did detect higher-than-expected amounts of metals in the eggs,” she said. “The Sparrow Swap program allowed us to get much wider access to these eggs than we would have otherwise, and we can use that to help protect both bluebirds and people where they live and play.”
The study, “Heavy metals and eggshell coloration in House Sparrow (Passer domesticus) eggshells across the Eastern United States,” is published in PLOS One. Co-authors include lead Suzanne Hartley and Kathryn Jewell, NC State; Mariah Patton, University of New Mexico; Chris Hawn, North Carolina Environmental Justice Network; Aubrey Wiggens, North Carolina Museum of Natural Sciences; Memuna Khan, Ripon College; and Daniel Hartley, George Mason University.
