There are many harbingers of Spring in Swoope; the yellow blooms of daffodils and forsythia, the sounds of spring peepers, and pastures changing from brown to green are only a few. My favorite harbinger of Spring is the arrival of Tree Swallows, Tachycineta bicolor. I start looking for them in late February. This year they arrived in Swoope on March 18.
Our Tree Swallows migrated almost 2,000 miles North from Florida and Cuba. They come here to breed and raise their young, returning South in the fall.
We maintain forty-eight nest boxes for them and other cavity nesters such as Eastern Bluebirds and Carolina Chickadees. There must be a hundred Tree Swallows along Trimbles Mill Road and the Middle River. There are often two or three birds around each nest box.
Anytime we drive a truck or tractor into a pasture it disturbs insects. The Tree Swallows come to get them. They are joined by Barn Swallows, Cliff Swallows and Northern Rough-wing Swallows in the feeding frenzy. It’s an amazing show of flight with colorful dives and swoops.
The College of William and Mary Research Team
We have always had a few nest boxes but in 2005 Dan Cristol, Chancellor Professor of Biology from the College of William Mary asked us if we would participate in a research project to study the biomagnification of mercury up the food chain. He and his students put up hundreds of nest boxes along the Middle, South, and North Rivers in Augusta County. On our farm, they added thirty nest boxes to the ones we already had.
Mercury Contamination of South River
Waynesboro, Virginia, was the site of a Dupont synthetic fiber production plant that discharged mercury into the South River from 1930 to 1950. The Middle and North Rivers were used as reference sites in the research because they didn’t have legacy mercury discharges in the River.
Tree Swallows Were the Main Species of Study
Tree Swallows were their main species of study because during the breeding season they eat only flying insects. Insects such as mayflies, dragonflies, caddisflies, and stoneflies spend their immature life in streams and rivers. The ones in the South River spent their aquatic life in the sediments contaminated with mercury. When these aquatic insects hatch from the water becoming flying insects, many are eaten by Tree Swallows. Subsequently, they feed their babies these insects and they, in turn, ingest the mercury.
Their groundbreaking research was published in Science magazine in the April 2008 edition. The article, “The Movement of Aquatic Mercury Through Terrestrial Food Webs,” states,
“Mercury is a persistent contaminant that biomagnifies up the food web, causing mortality, reproductive failure, and other health effects in predatory wildlife and humans.”
Their studies proved that mercury, in fact, does biomagnify up the food chain; twenty times higher than in the reference birds on our river.
Their six years of field research was, to their knowledge, “the first study to suggest disruption of multiple endocrine functions by mercury in wild animals,” one research paper attests. Cristol and his students published over fifty papers on their findings of mercury in wildlife.
Mercury Greatly Reduced Tree Swallow’s Ability to Withstand Heat
“The mercury-exposed swallows suffer a reduced hormonal response to stress, altered thyroid hormone levels, suppressed immune system, twenty percent fewer offspring annually, and most interestingly, a greatly reduced ability to withstand heat waves. Normally hot weather is great for them because of the increased number of insects flying around, but on the contaminated sites, that is when the babies tended to die…so there is trouble ahead when mercury and global climate change run into each other,” Cristol wrote.
The William and Mary field research ended in 2010 but we still maintain the nest boxes and added even more. It is a joy to see their metallic blue/green upper bodies and white breasts flying around the pastures in pursuit of insects.
Largest Natural Resource Damage Settlement in Virginia History
Their research was used as part of the South River/South Fork Shenandoah River Natural Resources Damage Assesment Plan which led to a settlement from Dupont of forty-eight million dollars to various environmental organizations to improve our landscape and waters. This is the largest natural resource damage settlement in Virginia history and the eighth largest in US history.
The College of William and Mary was a member of the South River Science Team that used research to understand, educate and reduce the effects of mercury in the South River.
We are very proud to have been a small part of this massive research project that resulted in some form of environmental justice for the decades of mercury contamination of a major river.
Really enjoyed this piece….it was well written
Nick, good to hear from you and thanks for posting your comment.
Isn’t science amazing! It outs the truth, fairly.
Yes, it is, Charlotte. Thanks for your comment.
Thanks, Bobby, for refreshing my memory on this important research. I am so thankful that there are still people willing to do this exacting, often tedious field data collection that adds so much to our big picture knowledge on contamination of the environment. That in turn can eventually lead to remediation, as in this case, although the mercury in the river sediments can’t be removed, it just continues to be diluted as it washes downstream. I pray that we’re smart enough to prevent the current anti-environmental cult from spreading. Those like you and your readers who love this earth and conserve wildlife and resources are my great hope.
Anne, thanks so much for your comment!
Wow. Interesting and eye opening research. Sobering to hear what they found. Good news that some restitution was achieved. Thankyou for your good work Bobby.
Beatrice, thank you so much for stopping in with your comment.
Really enjoyed this article Bobby. I studied new methods for detecting mercury in the sediment of the South River for my capstone project at JMU. I always enjoy understanding more of the history of the site and seeing how many people are trying to better understand the situation to both remediate and to attempt to not make the same mistakes elsewhere. I also appreciated the pictures. Swallows are one of my favorite types of birds and I enjoyed getting to see them still (a rarity)!
Joe, very nice to hear from you. Thanks for posting your comment.
Another great blog. Thanks, Bobby.
Thanks, Jeff! Good to hear from Delaware.
Enjoyed the blog, Bobby. I used to work for USFWS in the environmental contaminants program and I remember my colleagues in VA talking about this work with tree swallows. Cool stuff, so interesting that you were a reference site!
Beth, that is so cool! Thanks for posting your comment.
Bobby. I often fish the Middle River but never eat the fish. Is the Middle River contaminated?
Dan, the Middle River is not contaminated with mercury. It is, however; contaminated with sediment and E. coli.
As always a great post. Interesting about the mercury biomagnification and heat wave effect on the swallows. I remember quite a few years ago when science first started tasking about mercury in there oceanic food chain. I wonder if ocean temperatures rising has the same affect on sea creatures?
I wish the Dupont Settlement would grant money for ongoing monitoring projects. They don’t in fact consider that an important use of the settlement money…….better to rebuild a fish hatchery.
Bobby, your swallow pictures are great!
George, thanks for posting your comment. I truly believe that rising temperatures negatively affect ocean creatures. I have been with divers on the coral reefs off the Belizean and Costa Rican coasts and they tell me the coral is dying. Is it temperature rise or maybe suntan lotion; probably both and many other factors. Either way, it’s human-induced.
Thanks for your kind words and support, George. Your leadership is awesome.
Bobby, great writing and great photos. Beautiful bird. Hope you and Jeanne enjoy the rest of the Spring. Great time of year.
Thank you, Roger. And thanks for posting your comment.
Thanks for this excellent article.Tree swallows are such beautiful birds
You are welcome, Shay. Thanks for stopping in.
Wonderful post, Bobby! Thank you so much for sharing that part of your splendid environmental history. How wonderful to have played your part in that study, and the subsequent payment of monies to help in reparation.
Best to the both of you…and your lovely birdies!!
Thank you, Liz. Hope you and John are enjoying some warmer days.