Selenium contamination from Canadian coal mines may threaten Montana birds

Tree swallows act as a bellwether bird for scientists. Contaminant levels in their eggs can indicate something is amiss with the overall environment, so scientists often turn to them as an indicator. That’s exactly what is happening with these small birds in Montana.

Selenium levels in tree swallow eggs rose between 2022 and 2023 in Montana, according to a recent study. Levels of selenium, which are also increasing in Montana’s Lake Koocanusa and the Kootenai River, can impact reproductive viability. 

Even though selenium has little effect on human health, “it’s really dangerous for egg-laying animals. Lower levels of selenium will interrupt avian reproduction,” said Joe Skorupa, an author of the study and an environmental contaminants specialist at the U.S. Fish and Wildlife Service for 40 years.

“It’s really a Goldilocks nutrient,” said Skorupa, who investigated selenium levels in Lake Koocanusa. “It’s got to be just right or things don’t end well for animals.”  

Selenium pollution is a side effect of coal mining. Across the border in Canada, there are four active mines in the Elk River Valley — responsible for approximately 80% of the country’s coal production. Glencore Company owned these mines as of 2024, when they purchased Elk Valley Resources (EVR), a Canadian company. 

In October 2025, the Canadian government fined EVR $3.6 million for failing to reduce environmental toxins — selenium and nitrate — from polluting the Elk and Kootenai Rivers. 

In the new study, Skorupa’s colleagues set up 100 box nests (a type of nest used by tree swallows). Researchers wanted to create a baseline for selenium levels in tree swallow eggs at the sites in Montana and monitor the nests to see how many became occupied. Between 2022 and 2023, they collected 60 eggs from 98 occupied box nests and measured them for selenium.

While selenium levels in tree swallow eggs were measured at 3.1 milligrams per kilogram of dry weight, which is not high enough to disrupt reproduction rates, Skorupa said they need to be monitored. Researchers also discovered that birds occupied more box nests the further they were from the U.S.-Canada border and thus from the mining sites where selenium contamination is most prominent.

This latest study is part of a nearly 18-year effort to document selenium contamination in the Kootenai watershed, which the Montana Department of Environmental Quality (DEQ) began in 2007. According to Andy Ulven, the Montana DEQ water quality planning bureau chief, they first flagged Lake Koocanusa as a site affected by selenium contamination in 2012. “​​Sufficient credible data demonstrated that increasing selenium concentrations in both Lake Koocanusa and the Elk River in British Columbia had the potential to impact beneficial uses,” Ulven said in an interview. 

After higher levels were discovered in fish eggs in the Kootenai River, the DEQ adopted site-specific standards for selenium for Lake Koocanusa, the Kootenai River and fish tissues in 2020. They based these limits on the 2016 Environmental Protection Agency (EPA) national criteria. There were no site-specific standards for tree swallow eggs. The cap on the mineral in Lake Koocanusa, based on the effect on fish eggs, was set at 0.8 micrograms per liter and 15.1 milligrams per kilogram.

“For birds, it’s even more difficult to detect what’s going on, because you don’t see any signs of poison in the adult birds,” Skorupa said. “The young are dying inside the eggs; they never hatch.” He said that levels above four to six milligrams per kilogram are generally thought to disrupt reproduction in tree swallows. “When it gets higher than four, we start to get concerned.” 

“We support efforts, such as this study, to confirm selenium levels in the Koocanusa Reservoir are safe for birds,” Chris Stannell, who manages communications for EVR, wrote in an email. “Bird species have been monitored at the Koocanusa reservoir since 2016 with data consistently showing no signs of selenium-related impacts, and we expect these findings to continue.” 

Skorupa said that at Lake Koocausa, the data indicate that selenium levels are going in the wrong direction. Even when he shows mine operators and their scientific consultants evidence of it impacting wildlife, they often say, “If this pollution is so harmful, show us the dead bodies.” In Montana, selenium levels are not yet at this level. “The levels of contamination are low enough that whatever dead bodies there are at this point are probably larval fish. You can’t see larval fish. They’re microscopic,” Skorupa said. 

“Our mission is to protect fish, birds and wildlife. We don’t want to wait until after they’re dying,” Skorupa said.