Hi: Two days ago I was birding Cherry Creek Reservoir looking for the Yellow-billed Loon that was previously reported. About half way across the southern portion of the reservoir a loon was spotted. Because of heat waves the only impression that registered with me was the head was light brownish and the bill, appearing through shimmering light, was light colored.
I checked with Cornell Lab of Ornithology, Birds of North America series (an excellent resource) to see what the latest word was in distinguishing the difference between the Common and Yellow-billed Loon. Here is a brief summery of what I found Because of sexual and age variation in size between the two loon species, it would be challenging just using size as a distinguishing characteristic for either loon. Also because of the subtle variation in plumage for juveniles and non-breeding adults for both loons relying on appearance is tricky although could be highly suggestive for the Yellow-billed "Only characteristic diagnostic in all plumages and ages is color of culmen (ridge of upper mandible). In Common Loon in winter plumage this ridge and about 5 mm on either side is black (in breeding plumage the entire bill is black), but in Yellow-billed Loon at least the distal half and usually distal two-thirds is whitish-yellow" (Common Loon BNA series) Bob Righter Denver, CO -- You received this message because you are subscribed to the Google Groups "Colorado Birds" group. To unsubscribe from this group and stop receiving emails from it, send an email to cobirds+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/cobirds/3B9D2336-8D65-45AE-B61B-83034BF1104D%40earthlink.net.
