OK, Bird A didn’t fool anyone; both Molly and Wouter wrote in saying American Coot. Yep, that’s the one. The giveaway is in the feet. Each toe on our Bird A has several, well-demarcated lobes. This is distinct from grebes, which bear a single large lobe on each toe.
Bird B is superficially similar to the Coot, but the two are actually assigned to separate genera. Molly guessed Common Moorhen, and Wouter said Purple Gallinule, and indeed, those two species were the two that we were batting about in the SEANET office. I came down on the side of Wouter and Purple Gallinule. Here’s why:
Bird B has a two-toned bill–red with a yellow tip. This could mark it as either a moorhen or a gallinule. So we must go beyond that. Bird B is soaking wet, which notoriously darkens plumage, but there is still some iridescent green and purple evident over the neck and back, which leads us away from the duller-feathered moorhen. Finally, the legs are bright yellow, rather than the dull yellow of a moorhen’s legs.
We don’t see any of these three species often in the SEANET database, and they aren’t actually seabirds, which should place them beyond our purview. But who can resist a bird that looks something like a swimming chicken?