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Message: <blockquote data-quote="Mark B Bartosik" data-source="post: 3214550" data-attributes="member: 18843">I would like to hear on these subjects from these who have chance to observe Common Terns more often. In COTE Birds of North America (BNA) account following note is stated:Bill mostly black, often with crimson-red at base of lower mandible and below nostril (nonbreeding) becoming red or orange-red, with 12–18 mm black tip, often with variable amount of black on culmen or sides of upper mandible (early breeding), two-thirds red (egg-laying), and largely red (late chick rearing in late Jul). Black begins to develop again in Aug, and by mid-Sep may be largely black or still largely red. Rarely bill has minute yellowish tip or is mostly black throughout breeding. Three- and 4yr-olds have more black on bill than older adults at same dates.As we can read largely red bill can be found in late July. On May 7 and 8 I had an opportunity to spent time with huge COTE migrating flock (read more details in this post if interested: <a href="http://www.birdforum.net/showthread.php?p=3214507#post3214507" target="_blank">http://www.birdforum.net/showthread.php?p=3214507#post3214507</a>) - about 20 plus thousands birds so I could to try find some interesting individuals. Only a very few subadults were present but it was a bonanza for adults in full breeding plumage. As you can see in this composite photo (that include examples of subadults and adults head patters and bill coloration found on May 7 and 8)<a href="http://www.pbase.com/mbb/image/160005621/original" target="_blank">http://www.pbase.com/mbb/image/160005621/original</a>It was possible to find not even only largely red but practically all red bill in adults (bottom right). About 2.5 months earlier from what published records suggest. BTW this can be confusing as at the same time Arctic Tern has bright red bill and it is not always possible to analyze bill structure when viewing from a farther distance.  Also I found another interesting case, at least to me, second photo in bottom row, of individual with all red mandible and well defined black tip on maxilla.So I will read any opinion about what others observed (and perhaps photographed) regarding variations in COTE bill coloration as well as about timing of bill color changes.Cheers,Mark</blockquote>

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