Caspian Tern, Hydroprogne Photo by Fran Morel

A strikingly elegant creature is the Caspian Tern.

In 2006, two years before I began writing about birds for the RoundTable, a friend who lives by the lake asked me to identify the beautiful birds that flew by every summer morning. She described them as fairly large white birds about the size of a gull. with a black cap and a big heavyset orange bill that was almost always pointing down to the water. She had observed their graceful, powerful flight. I had no trouble identifying them as Caspian Terns.

Having learned their name, she peppered me with questions. They must be migratory, she observed. Where did they spend winters? (Coastal areas from the southern United States south to northern Colombia and Venezuela). What do they eat? She would see them appear to be fishing in the mornings – flying over the lake not too far from shore, hovering, plunging into the lake, and often coming up with nothing. (They primarily eat fish, whatever is available seasonally, alewives and smelt are favorites.) What do they do when not fishing? (They hang out alongside the gulls on the beach or on the groins jutting into the lake, keeping to themselves.) Are they monogamous? (Typically, yes.) Where do they nest? (That I didn’t know, possibly near Lake Calumet. I only knew they typically nest in huge colonies, and that their nests are just a scrape in the sand or gravel). I did know that they have been found on all continents except Antarctica.) Is it really named after the Caspian Sea? (Yes, but their Latin genus name, Hydroprogne, translates to the more apt “water swallow.”)

 I knew a bit about these terns because, back in 1999, a controversy had erupted over Caspian Terns nesting on Rice Island in the Columbia River in Oregon. Caspian Tern colonies can number in the thousands. The huge number of birds was unwelcome. The problem was a clash between the U.S. government-hatched salmon and the birds: both like to return to their breeding grounds. Hatchery and wild salmon returning upstream had become 90 percent of the terns’ diet. The proposed solution was to move the Caspian Tern colony to East Sand Island, closer to the marine waters of the Pacific where there would be a greater variety of fish species. Moving the colony included destroying nesting sites and eggs and laying wire deterrents and generally annoying the birds at Rice Island while simultaneously attracting the birds to nest on East Sand Island. Seattle Audubon, National Audubon, American Bird Conservancy, and Defenders of Wildlife filed a lawsuit against the Corps and NOAA (National Oceanic and Atmospheric Administration) Fisheries, maintaining that the plan was insufficient and that eggs should not be destroyed. A settlement was reached in 2002.

Our route for visiting Lewis and Clark sites in the Pacific Northwest included crossing the bridge from Oregon to Portland at Astoria. East Sand Island is visible from the bridge. Curious about how the moving project was working, we had contacted the researchers in advance and were invited to join a workday on the island. Arriving at 11 a.m., we were given waterproof boots, ushered into a boat and set to work removing decoys that had been placed on the island to lure the terns. It was the end of the season; the staff explained everything there was to know about terns and the project. The move worked; the tern colony moved to East Sand Island and their intake of salmon was reduced by half. That visit was on September 11, 2001.

While researching where Caspian Terns were nesting in southern Lake Michigan for this article, I learned that Caspian Terns had been using the roof of Chicago’s Jardine Water Purification Plant, next to Navy Pier, after that plant was expanded. Free from ground predators, a roof makes their eggs and young safer except for avian predators.

They were not welcome there, either.

According to Harold Keaton, a Filtration Engineer at the plant, purification is accomplished using chlorination, sedimentation and filtration to meet the EPA’s drinking water standards. But there was a problem. The flat, pebbly roof appealed to nesting Caspian Terns; pebbles are as good as sand for their nests. The colony grew. When it rains or snows, the roof drains directly into the sedimentation basins, bypassing the intakes and prior water treatment. This untreated runoff could potentially cause the treatment plant to exceed the EPA rules for cryptosporidium removal from the water by chlorine. Adjusting the proper amount of chlorine to be applied is tricky because of weather – rain and temperature alter the conditions. Cryptosporidium is a microscopic parasite. Its presence in the water supply is an enormous issue. Cryptosporidium from a water plant was implicated in the 1993 Milwaukee Cryptosporidiosis outbreak that caused illness in over 400.000 residents served by the plant.

The managers of the water plant were taking no chances. To eliminate the nesting Caspian Terns, the plant installed gridwire on the roof. The gridwire worked. The tern colony has disappeared. and they appear to be nesting at a former nesting site at the Arcelor Mittal Steel plant in East Chicago, Indiana,

They continue to fish wherever there is shallow water. Evanston’s lakeshore, the North Shore Channel and the Skokie Lagoons are good spots to watch for these beautiful birds.

Libby Hill is the author of "The Chicago River: a Natural and Unnatural History. She has been writing about birds and trees and Evanston's natural history for the Roundtable since 2004.