Raptors Fall Prey to Microplastics

 A Red-Tailed Hawk at Dixon Lake, California. Photo by Shea Vavra

CAL POLY RESEARCHERS FIND MICROPLASTICS IN EACH CENTRAL COAST BIRD THEY EXAMINED

BY NICK WILSON
APRIL 2025

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Assuming roles akin to wildlife pathologists, a Cal Poly professor and student researcher spent months tackling a biological mystery. 

Their case? To determine whether three red-tailed hawks, four red-shouldered hawks, two great horned owls, and seven barn owls had consumed microplastics before their demise. 

To do so, their work involved examining the digestive systems of the 16 deceased raptors that once roamed California’s Central Coast. 

The inspiration for biological sciences Professor John Perrine’s study came from an academic journal article published in 2020 by researchers who examined 63 deceased birds of prey in Central Florida and found microplastics in the gastrointestinal tracts of every bird they surveyed. 

Perrine and student researcher Alexis Leviner (Animal Sciences, ’21), who minored in biological sciences, used the same protocols from the Florida study and carefully inspected raptors on the Central Coast, hoping to expand awareness about a topic lacking comprehensive information. 

They chose birds of prey because of their terrestrial dietary habits. Most microplastics research has been conducted in aquatic environments due to the prevalence of marine-related pollution. When plastics break down in these environments, the small particles are ingested by filter feeders and then enter the biological food chain. 

 Alexis Leviner searches for microscopic evidence of ingested
 microplastics in a deceased raptor. INSET: Evidence of microbeads
found in the system of a raptor during examination. Courtesy photos

“Our study has no clear connection to aquatic filter feeding because we focused on predatory birds that eat terrestrial prey such as rodents and other birds,” Perrine said. 

They published their results in the peer-reviewed scientific journal California Fish and Wildlife Journal, with Leviner taking the lead as the first author. 

Coordinating with Pacific Wildlife Care, a Morro Bay animal rescue center which supplied the birds, the researchers also ensured that no bird had been fed while in captivity, which could have introduced microplastics into their digestive systems. 

No animals were harmed for the study, as they’d suffered fateful window or vehicle strikes, leading to broken limbs, and had been humanely euthanized within 24 hours of intake due to poor prospects for recovery. 

Between February and August 2021, Leviner conducted extensive lab work under Perrine’s supervision. Leviner took painstaking steps to thoroughly study the carcasses, searching for microfibers, microbeads and microfragments. 

To avoid microplastic contamination, Leviner wore cotton clothing; used metal, ceramic or glass materials; and carefully purified water to clean flasks and other research materials, among other precautions. 

Supported by the William and Linda Frost Fund, benefiting Cal Poly student research, Leviner spent 40-hour work weeks over the summer inspecting the samples. 

Working with the supplied carcasses, Leviner extracted gastrointestinal (GI) tracts, dissolved the biological tissues in potassium hydroxide solution and filtered them using a vacuum pump, and then examined the undissolved microplastics on the filter paper. 

“I liquefied the GI tracts into a solution,” Leviner said. “I would place these samples into a shaking incubator. They’d sit in there for 48 hours, 40-degrees Celsius, shaking the samples at 65 revolutions per minute to maximize that digestive process.” 

Magnifying the samples on filter paper, the evidence became clear. Like the Florida study, the digestive tracts of all 16 birds examined contained microplastics, totaling between three and 20 pieces each. 

Of the 196 microplastic particles they observed, microfibers were the most abundant (58%), followed by microbeads (34%), and microfragments (8%).

Even though microbeads have been banned in California since 2020, they were found in all 16 birds. Additionally, microfibers were found in 15 birds and microfragments in six birds. 

Where were the birds consuming microplastics? How might their physiologies be affected? How can humans avoid polluting food sources? 

The chemical composition and source of the contaminants remain unclear, along with the physiological and ecological implications to raptor populations and their ecosystems. Future studies could help gain a better understanding. 

“Throughout the whole project, our goal was to isolate these plastics and document them in our local raptor population,” Leviner said. “But there are so many other implications that should be examined to learn more.” 

Leviner noted that trace amounts of plastic observed were not the causes of raptor deaths. 

Still, microplastics threaten multiple systems, so it’s critical to “gather baseline data and try to understand the risks that microplastics pose to environmental, human, and animal health,” Leviner added. “Our current uncertainties lie in the biochemical impacts of long-term exposure to microplastics, which can carry additives that serve as endocrine disruptors — which ultimately means altering the hormones produced in living organisms. This could have negative implications on reproduction or metabolism, for example.” 

Leviner, who currently works in a veterinary clinic and plans to begin veterinary school in the fall, added: “I was really interested in necropsy, which is essentially performing an autopsy on a non-human species. This is work that some scientists, biologists and veterinarians perform. I definitely still have an interest in pathology, and a love for research.” 

A Red-Tailed Hawk at Dixon Lake, California. Photo by Shea Vavra

RESEARCH SUPPORTED BY: William and Linda Frost Fund, Pacific Wildlife Care