Ospreys love baling twine and like filling their nests with pieces left behind in fields from hay bales. Only problem is, the colorful plastic twine can kill them.

Adult birds’ sharp claws can get so tangled that biologists at the University of Montana have documented birds getting caught by the foot and, unable to escape, end up dying hanging upside down from their nests. Chicks die when they get tangled in the orange polypropylene twine.

Estimates are that in some places baling twine can kill 10 percent of osprey babies and adults, said UM wildlife biology professor Erick Greene, who helps run the Montana Osprey Project.

Discarded fishing line can also get birds “hideously tangled” and kill them, Greene said.

Those are just two ways that wild birds are endangered by plastics — a danger that’s the focus of this year’s World Migratory Bird Day.

The theme for 2019 is “Protect birds — Be the solution to plastic pollution.” More than 750 events are being held in nearly 80 countries to heighten awareness of migratory birds and the danger of plastics.

In Bozeman the 800-member Sacajawea Audubon Society is holding free events Friday and Saturday to celebrate Montana’s migratory birds and highlight the perils of plastics.

On Friday at 7 p.m. Sacajawea Audubon will host a free showing at the Ellen Theatre of the one-hour “Epic Yellowstone: Life on the Wing” about the birds of Yellowstone. Filmmakers Tom Winston and Jeff Reed from Grizzly Creek Films will talk about the making of their documentary, which has been broadcast on the Smithsonian Channel, and Audubon leaders will announce a new project.

On Saturday from 10 a.m. to 1 p.m. at the Bozeman Public Library, Sacajawea Audubon will hold a free public festival celebrating migratory birds.

There will be educational games for kids, making origami birds and bird feeders, face painting, bird books and a demonstration of bird-friendly landscaping. There will be information on recycling, the chance to tour a nearby wetland bird haven, and the Montana Raptor Center plans to bring live birds for kids to meet.

To encourage using alternatives to plastics, the festival will give away metal straws to replace plastic straws and cloth bags to replace plastic bags.

“Plastics are a planetary problem,” said Audubon member Karin Jennings.

One of the big dangers from plastics is that birds can mistake plastics for food and it can fill up birds’ stomachs, said Loreene Reid, past president of Sacajawea Audubon. The plastics clog up the birds’ digestive tracts and keep them from getting enough food to grow or migrate successfully.

“There’s not a time we go out birding that we don’t pick up plastics,” Reid said.

Audubon members have seen ducks with their feet tangled in plastic bags or six-pack rings.

Plastics also can harm birds’ hormone and reproduction systems, said Billy Burton, a Sacajawea board member. Discarded plastics break down in the sun and tiny pieces of plastic end up in the gullets of birds and fish and go up the food chain.

Discarded monofilament fishing line presents similar hazards, Reid said. It can end up wrapped around birds’ feet or necks, or they can eat it.

Baling twine and monofilament fishing line “basically last forever,” Greene said from his Missoula office.

Most ranchers are very careful to pick up twine because they don’t want their cows to eat it, and horse owners are also careful, Greene said. But if one hobby farm leaves baling twine in a field, osprey will travel miles to collect it. Most osprey nests end up filled with yards of orange baling twine.

Fishing line also presents a huge problem in Montana, Greene said.

“It ends up in rivers in big tangles. Lots of things die — ducks, geese, osprey, king fishers, eagles. We had a bald eagle two weeks ago all tangled in fishing line.”

A great horned owl that got tangled in fishing line was photographed dead, hanging upside down from a tree.

To help solve the plastics problem, Sacajawea Audubon members are urging people to collect and recycle old bailing twine and fishing line.

They’ve started putting up fishing line collection posts at fishing access sites, like the Missouri Headwaters and Harrison Lake. The collection posts are L-shaped PVC pipe. People can place discarded fishing line inside the top of the post and the club members will collect it later.

“Everybody hears about the plastic islands in the ocean,” said Terri Narotzky, a festival committee member. Just because Montana is far from the ocean, she said, it doesn’t mean we’re not part of the problem.

“Our plastics float all the way down to the ocean,” Reid said.

One solution is to recycle plastics, but that has become more difficult as recyclers cut back on accepting plastics. Emma Narotzky, Audubon education committee member, said clear clamshells are no longer accepted because they look like cardboard to the sensors that sort recyclables. One answer is to pressure stores to find another packaging option. People also need to do a better job cleaning the plastics they do recycle.

Another solution to plastics is to minimize use and avoid using them in the first place, Burton said. Bring reusable bags to the grocery store and replace plastic water bottles with reusable bottles.

Hundreds of scientists issued a United Nations report this week saying that human activity threatens more than 1 million species of plants and animals with extinction. Scientists calculated that 1,492 bird species are endangered.

In Montana, Audubon members said, there are 18 bird species of concern, including Lewis’s woodpecker and the American bittern.

Montana is part of the Pacific Flyway, the pathway that millions of birds travel each year from breeding areas to wintering areas and back.

Birds like the Swainson’s hawk live remarkable lives, spending winters in Argentina and flying 4,000 miles back to Montana to breed. Even tiny hummingbirds — “just a spoonful of feathers,” Burton said — migrate as far as Central America, flying up to 400 miles a day.

“The reason I live in Montana,” Burton said, “is because of the incredible wildlife.”

Gail Schontzler can be reached at gails@dailychronicle.com or 406-582-2633. Follow her on Twitter @gailnews.

Gail Schontzler covers schools and Montana State University for the Chronicle.