Hi anniesmom----I absolutely found this to be true this spring with my SFHs. I was so excited to get eggs, I was sticking everything in the incubator. The hatch rate at first wasn't so great and the eggs were fairly small. The ones from the smallest eggs are still smaller than the rest. After about two months the egg size was much bigger and I was getting almost 100% hatch rate. It was the same with some shipped eggs I got. The tinyest eggs didn't hatch at all and one very small chick that did hatch, died.
I've got my scale set to grams and 50+ grams seems to be a good weight. (That's 1.76 ounces according to a chart. Two ounces is about 56 grams and would be even better.) From now on I won't try to hatch anything smaller than that.
My GF Legbars are doing great. I gave one of the 4 boys away and another is penned by himself for now. The girls just weren't ready for HIM yet! They will be 18 weeks on Monday and I've got some big red pullet combs already. I saw one of the remaining 2 cockerels in with the 8 pullets breed one of them this morning. There was no squawking. She just let him.
Really true, and for a breed that is "rare" and/or endangered, the luxury of waiting etc. may not be an option. I think the California Condor was down to something like 11 birds at one point, and the Whooping Crane the same like 20 or 29 left before extinction. There are some cases where--- just to continue the genetics if possible is worth the throw of the dice.