Very productive few day it seems to have been, now I feel guilty for having a nap, the divers are spot on (ie they look just like my dreams of this species) as for the gulls, well, it's not fair!! perfectly proportioned with just one single outline! When I sketch gulls they always end up looking like something that should be viewed with 3D specs.
The composition is developing well, I'd like to see more space in front of the left hand birds as they seem a little squashed up into the edge of the picture, don't know what the reflections are to be like but maybe the opportunity for them to be important in the composition??
Go for the large size, you know you want to!
Having difficulty myself with a similar idea, involving RC Pochards. Suppose I should get off the internet and start painting!