Herring Gulls Are Sentinels of the Skies

By Kevin Bunch, IJC

herring gull
A herring gull sits on its nest of eggs on the shoreline of Saginaw Bay. Credit: US Fish and Wildlife Service

Since the 1970s, Great Lakes researchers have had a friend to help them learn more about chemical pollutants in the waters and food chain: the herring gull. With old contaminants phased out and new ones entering the system, sampling these sentinels of the skies is more valuable than ever.

The Canadian Wildlife Service – part of Environment and Climate Change Canada (ECCC) – has collected gull eggs from 15 sites across the Great Lakes basin each spring since its Great Lakes Herring Gull Monitoring Program began in 1974, according to Robert Letcher, an ECCC research scientist on chemistry and ecotoxicology.

“The herring gull was chosen given its presence and breadth of nesting sites across the Great Lakes,” Letcher said. “And because the herring gull sits atop the aquatic food web – it’s a fish-eating bird, a top predator – it’s a good indicator species, or sentinel, on what’s getting into the aquatic food web from a chemical standpoint.”

This binational effort by Canadian and US scientists to sample gull eggs has proven to be a cornerstone indicator of Great Lakes health. A State of the Great Lakes 2017 report from Canada and the U.S. used herring gull eggs as an indicator for pollutants, with its data echoed in the IJC’s first Triennial Assessment Report.

Researchers check gull eggs for contaminants passed down by bird parents (a process known as bioaccumulation), and can gauge the presence of bioaccumulated contaminants in species up the food web. They also look at shell thickness, check for embryo mortality and fetal deformity, get an idea of how many gulls are using a particular nesting site – all indicators of reproductive health – and use atomic isotopes to understand how gull diets have changed over time.

Researchers then compare these factors between colony sites. Since the sample sites and lab work have been largely consistent over the course of the program, Letcher said, a comprehensive archive through time has taken shape. The samples are held long-term in the National Wildlife Specimen Bank in Ottawa where they can be sub-sampled for other chemicals that may become more prominent in the years after they were collected.

The US Fish and Wildlife Service (USFWS) has assisted the Canadian Wildlife Service and ECCC in collecting eggs from some colonies throughout the life of the program. More recently, it worked with the state of Michigan to add an additional 10 sites on the US side of the lakes, said Lisa Williams, environmental contaminants branch chief and biologist with the USFWS Ecological Services Field Office in Michigan. Samples from the United States are typically sent to the same ECCC lab to keep the analysis and scientific methodology as consistent as possible, and also held in Ottawa. Funding from the US Great Lakes Restoration Initiative has been critical in expanding the number of sites and chemicals analyzed.

Legacy contaminants that were on the scene when the program first started, such as polychlorinated biphenyls (PCBs) or DDT, have long since been banned, and concentrations saw steady decreases in the late 1970s before flattening out in the past decade, Letcher said. Contaminants phased out more recently such as polybrominated diphenyl ethers (PBDEs) have shown signs in recent years of decreases in herring gulls, due to the time lag in the chemicals moving through the system.

pcbs fish
Levels of PCBs have declined in herring gull eggs and fish since 1975, but have leveled off above the zero point in the past decade. Credit: IJC Triennial Assessment Report, Draft State of the Great Lakes Report as presented at the Great Lakes Public Forum

On the flip side, mercury amounts haven’t decreased much since monitoring started in the 1970s, Letcher said. And with a constant churn of new chemicals entering the lakes all the time, more contaminants are being examined using the herring gull eggs.

These include polyfluoroalkyl substances (PFAS), perfluorooctane sulfonate (PFOS) and related chemicals. PFOS were phased out by producer 3M in the early 2000s but are still produced elsewhere in the world, and as such concentrations haven’t dropped in gull eggs over time, Letcher said. The urban landscape still contains large amounts of PFOS and PFAS chemicals that are getting into the lakes and food web.

Some sampling sites have been dropped from research due to birds abandoning them because the location has degraded, such as Fighting Island on the Detroit River, or from natural changes in nesting preferences, Letcher said. But other colonies, like those on the mouth of the River Raisin in Michigan, can see year-to-year swings in reproductive success, Williams said. Those sites continue to show indications of depressed immune systems in the gulls, even as legacy contaminants decrease. This suggests that with enough stressors in a given year, the birds won’t achieve as much success reproducing, Williams said.

Williams said research also suggests that herring gulls in contaminated areas may have descended from gulls who were more tolerant of these chemicals and thus were able to reproduce successfully, though that may have come at the cost of other aspects of their health.

“Herring gulls can be our canaries on the Great Lakes,” Williams said. “They can also help us learn, when compounds are being phased out, how rapidly the system can respond to that phase out, and when concentrations drop beneath the level of concern.

“The take-away message of this is not to release bioaccumulative chemicals into the environment.”

Kevin Bunch is a writer-communications specialist at the IJC’s US Section office in Washington, D.C.

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