Blue-footed Booby (Sula nebouxii) 19 September 2013 Seal Rocks, Cliff House, San Francisco, CA Photos © 2013 Joseph Morlan
Peter Pyle agreed writing, "I agree that it has begun a molt, with p1 growing or new, as best seen in image 497 but ascertainable of both wings in all images. The left central rectrix (r1) has also been replaced, as possibly have several wing coverts, and one or more tertials may also have dropped. This would all make sense for a bird beginning the second prebasic molt, and would indicate a bird of 8 months of age according to the literature. If so it may have hatched in January or February, and for a booby subject to so much solar exposure, this easily explains the wear on the rectrices and other flight feathers. I see what you mean about the s3 but since this does not show up in any of the other images or the right wing, I think it's an artifact of the image. The first secondary besides tertials to drop in boobies (and most large birds) is usually s5 (occasionally s1) and this feather looks the same as the others. The substantial uniformity of the flight feathers otherwise still convinces me that this bird is an HY just beginning the PB2. I've linked a couple of older flying BFBOs that I found on line, for comparison of flight feathers."
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