Ginger, thanks for getting a good look at the fishing line coming from DN18's mouth. It's really fine, but it would take some effort to break it. RRP will know what to do, including getting up to the nest and cutting the line, then hoping the part inside the bird passes on through without a problem.
Here's a pic of the binder twine from FEB 19th when it first appeared at the nest. This type is natural material, but it is very hardy and would take several years to degrade in the weather. The plastic versions are a menace, and I'm glad this farmer doesn't use that type -- usually pink or green.