One of the biggest mysteries is the modern world’s impact on snowy owls – here and in the Arctic.
Even in the most remote parts of the Arctic, wind-borne contaminants have been detected in many species. And when snowy owls come south, they may be exposed to a host of toxins that can affect their health, especially the potent and deadly new generation of rodenticides.
Dr. Sherrill Davidson, center, and Dr. Erica Miller, right, conduct a necropsy on a snowy owl that was found dead. (©Louisa Shepard)
Collaborators in Project SNOWstorm, working under federal, state and provincial permits, take blood and feather samples from many of the owls they capture, and federal and state wildlife agencies are providing the carcasses of owls that were found dead. An international team of wildlife pathologists and veterinarians necropsies the dead owls to determine the cause of death, check for diseases and parasites, and take tissue samples to test for a wide range of environmental toxins like lead, rodenticides, mercury and pesticides. By 2022 we and our colleagues had necropsied and tested nearly 400 salvaged owls, the largest and most thorough examination of the health and condition in wintering snowy owls ever.
One area of concern are the alarming levels of mercury that we have detected in many snowy owls. Mercury enters the environment from a variety of sources, including waste incinerators, chlor-akali factories and paper mills, but the largest source in North America are coal-fired power plants. Drifting on the air, it travels around the globe, eventually precipitating into waterways and oceans. Worse, it bioaccumulates in the food chain, so that with each jump up the chain the mercury concentration rises, reaching dangerous levels in top predators like owls. Mercury concentrations in loons and other fish-eating birds on which snowy owls prey can be 10 million times the level in water.
We have also found that roughly half of all snowy owls tested carry detectable levels of DDE, a breakdown product of the long-banned pesticide DDT. What effect this may have on the owls remains a mystery that we are exploring.
Most concerning, however, is the rapid increase we have seen in the past 10 years in the frequency and rising rates of anticoagulant rodenticides in the snowy owls we have tested. These rat poisons are an insidious threat to all raptors, and the danger is increasing annually. By 2023-24, more than half the snowy owls we tested had what are potentially lethal levels of rodenticide in their systems. The problem seems especially acute in the Northeast.
We are completing an in-depth analysis of all of our snowy owl health and mortality data with Dr. Nicolas Lecomte and his students at Moncton University in New Brunswick, which will illuminate what environmental contaminants are putting their birds at greatest risk.
