Danger In the Nest: Osprey and Baling Twine

For the last six years, an adult Osprey pair – “Charlotte” and “Charlie” - have delighted viewers around the world as they build a nest and attempt to raise a family each year on the nesting platform in Charlo, MT. Charlotte and Charlie have successfully raised 11 chicks since 2016.

This year, Charlotte and Charlie first appeared in mid-April, when they migrated thousands of miles back to Montana from Central or South America where they spend the winter. After spending some time bonding and getting their nest into tip-top condition, Charlotte laid two eggs. They kept the eggs warm by incubating them for over 5 weeks. Those eggs hatched around June 13 and 16. Right around the same time, Charlie brought baling twine into the nest.

Two osprey chicks in a nest. One is badly tangled in baling twine.
A picture of the two osprey chicks in the nest, before the twine was removed the first time. The younger, smaller chick is at the edge of the nest near the top of the image. The older, larger chick is in the center of the image entangled in orange baling twine. They are less than two weeks old and still completely reliant on their parents for survival.

What is baling twine? How do Osprey get it?

Baling twine is a strong, thin rope that is used to hold together bales of hay. Today, it is most commonly made of many fine strands of polypropylene, a plastic polymer. Polypropylene baling twine can take half a century (or longer) to break down- much longer than the natural lifespan of an Osprey. When discarded baling twine is left in a field or pasture, Osprey will pick it up to use as nesting material, lining the nest and building it up. This can have devastating consequences for the birds.

Why is baling twine dangerous for Osprey?

Osprey sometimes use bits of human refuse as nesting material: bathing suits, flip-flops, fishing line and plastic balloon ribbons, rubber gloves, a copy of the local newspaper still in its plastic bag—and their favorite here in the West: baling twine. It is thought that Osprey consider these to be similar enough to their natural nesting materials that they pick them up and bring them home. Baling twine is abundant in many Osprey nests on artificial platforms near agricultural areas where it is commonly used, as Osprey pick up nesting material from within about half a mile of their nest.

Since baling twine is plastic, it is extremely difficult to snap or break, and it doesn’t break down quickly in inclement weather—qualities that make it ideal for holding together hay bales, but can be deadly for Osprey if they get tangled in it. Though Osprey have sharp talons and beaks, they’re not sharp enough to cut through the twine—Osprey talons meant for puncturing and ripping apart fish, not cutting through rope (think ice picks, not box cutters).

Adult Osprey tangled in baling twine can become unable to fly and trapped in their nest (or stuck dangling from the nest) or can slowly lose toes—or a leg—due to cut-off circulation. When the chicks are tangled, they are less able to move around in the nest, which means they are less able to get to food their parents bring back, and they can slowly be outcompeted by their larger siblings and starve. If the baling twine is wrapped tight around a leg or wing, the chicks can lose limbs or toes, which means they won’t be able to hunt and will slowly starve if they make it to adulthood. It’s estimated that up to 10% of osprey chicks in the West will die from baling twine in the nest.

See Montana Osprey Project FAQ, Baling Twine and Raptor View Research Institute: Baling Twine Project for more information on why baling twine is dangerous for osprey nests in Montana.

Baling twine in the Charlo Osprey nest

We had been monitoring the baling twine Charlie brought to the nest, and quickly sought advice from local Osprey and raptor expert Rob Domenech, the executive director of Raptor View Research Institute (RVRI), who explained that disturbing the nest with such young chicks could be detrimental and is generally not advised. Typically the chicks don’t get tangled until they are a bit older and, moving around the nest. RVRI planned to make the trip to Charlo the next week with a bucket truck to access and clean the nest. However, when one of the chicks was tangled in the twine, we had to act quickly to find a local tr