Many thanks, ANDERS, for Your Fine, Sharp
profiles of this slaty couple
-- world.s smallest Grebe (L.1766).

Perhaps Your photo adds to some field guides' characteristics of this species.
Cf. below.
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Absolutely unfamiliar with this bird,
I looked it up in Sibley.s and Bertel Bruun.s
US guides and Raffaele.s on the West Indies.

For the first time ever, I notice that SIBLEY
may be a bit out of tune:

In absolute contrast to YOUR .upper. bird
and Bruun.s and Raffaele.s illustrations,
SIBLEY shows specimens with a SLENDER bill,
somewhat like Black-necked (=Eared) Grebe.

and verbatim states THIN straight bill.
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Interesting, too, that NONE of these field
guides show bills with a WHITE tip,
although You and a few other photographers
display this feature.

Only present in some birds, in peak breeding
season ?

NB:
Difficult to determine, if Your .lower. bird
(male?) indeed has a LONG white tip(!)
or just appears so, for other reason ?

Best rgds. ......... C.