Domestic Duck mix

In fact the first two ducks I have on this also have dark bills.

Thank you Liam. I added another odd one to the bunch. I was with some birders from Golden Gate Audobon and they thought this maybe a hybrid domestic too but were confused on the bill. It was smaller then the other domestics plus it has a dark bill instead of an orange one.

All are Anas platyrhynchos - Mallard. Domestic form and wildtype forms do hybridize, but most of your ducks appear to be domestics. A Blue Swedish-type in the first and second photos, Black Swedish and maybe a Rouen in the third, and a Buff-type in the final.
Most, if not all, probably have other breeds in them (i.e. grandparent may have been another breed).

Thank you Scott...informative link

This is a great little article about "manky" ducks or domestic/mallard crosses. I refer to it often when I see something odd at my local pond: http://10000birds.com/manky-mallards-dom...

The other two also look to be hybrid, but what species I am not sure.

The pictures of the single ducks facing to the right show dark bills so that makes me unsure of them but the picture of the pair and the one facing to the left do look to be mallard/hybrid. I have some pictures that look similar to those. Note the yellow bills.

Jellis, I agree that they appear to be hybrids, though I am not 100% sure on all of them. Liam might be able to give a bit more insight.