If you spent time at the beach this summer, you probably encountered seagulls screeching overhead and eating trash. You probably also encountered their poop. Seagull droppings can carry disease-causing microbes like Escherichia coli and Enterococcus, which can contaminate beaches and water. Now scientists have found a way to fight back: Release the hounds. In a new study, researchers show that unleashing dogs keeps the seagulls away -- and the water at the beach free of microbes.
Beach managers have been fighting seagulls for decades. The more birds, the more microbes, and the more likely the beach will meet the guidelines for closing, as advised by the Environmental Protection Agency (EPA). In a recent study, researchers from the U.S. Department of Agriculture tried reducing gull populations on Chicago beaches by "oiling" their nests -- spraying oil on the eggs to prevent the birds from hatching. That tactic had some short-term success, but its long-term benefits are unclear. Chicago beach managers have also used dogs to chase away gulls, which anecdotal evidence suggests has helped reduce the microbe counts and thus the number of beach closures.
To more definitively connect the gulls' dog-inspired dispersal to microbe concentrations, a team of researchers led by Reagan Reed Converse, an environmental microbiologist at EPA in Chapel Hill, North Carolina, examined water quality at North Beach in Racine, Wisconsin. During the summer, managers regularly "groom" the beach, located on the shores of western Lake Michigan about 100 kilometers north of Chicago, by turning over the sand, which buries any microbes left from bird poop. North Beach's managers have also worked to remove other sources of pollution, such as sewage runoff, leaving the gulls as the primary source of contaminants in the water.
The team collected beach water samples for the first 11 days of August 2011 to get a baseline bacterial count. Then, they sent in the dogs. One such hired dog posse, made up of one or two trained border collies and their human handler, chased ring-billed and herring gulls away from the sand from sunrise to sunset. (The handlers make sure that dogs leave endangered species, such as piping plovers, alone. They also collect the dogs' poop.) After a week of similar beach clearing, the researchers began sampling again -- while the dogs kept patrolling -- until August 27, for a total of 9 relatively gull-free days.