Do blue tips on the bills of European Starlings mean anything? I notice a difference across time and across birds. In Birds of the World/European Starling/Plumages, Molts, and Structure I read that breeding adults have yellow beaks, that in males “the base of the lower mandible is bluish or blue-gray” and in females it is pinkish. However, more research of the literature suggests that these indicators are not definitive. I agree.
I can’t even find this difference in a flock of starlings perched in a tree. And I’ve examined many. See my checklists on eBird. Here are some of my photos to show what I’m talking about.
Most starlings I see have dark bill tips, though it’s hard to say if it’s a stain from dirt (as their bill tips always go in the ground) or actual colour, both males and females have dark tips, the only all-yellow bill on my photos is https://www.inaturalist.org/observations/27198836
The bill darkens after the breeding season to dark gray-brown or black with the result that by early winter only 5%–10% of birds have yellow bills.
Bills of adult males begin to turn yellow in late Dec, followed by adult females, then first year birds. Yellow appears first near the base of the lower mandible and progresses to the tip as a result of bill wear.
Your photo is a different bird: Black Sea Starling. Bill especially looks different with black along the base. I accept Swampster’s scientific answer since it is more consistent with the appearance of the bills than stains. Locally, the ground has been frozen and covered with two inches/5 cm ice for the past month or so. Stains would have worn off by now. Nor would they all look exactly the same on all the birds.