We have 11 hens, two in one coop and nine in the other. Of the flock of nine, I get no more than 8 eggs on any given day (less lately, as it's been hot). In that flock I have 4 black australorps, 1 yellow and white Easter Egger, 1 Rhode Island Red and 3 red stars. No one has the makings of a roo...no spurs, no one's bigger, has larger tail feathers, and no one crows. And yet...this morning we cracked about 8 eggs from the fridge, and all the brown ones (which can only come from this flock as my other two hens are Easter Eggers) looked fertile, with that characteristic white spot on the yolk! How is this possible? These chickens are all about 15 months old, and no one has ever showed "male" signs. Is there anything else that can look like a fertile spot but really be something else? (None were bloody like capillaries were developing, but I've also never seen anyone get broody to get a fertile egg to that point.) I'm so confused!
It's the bullseye AROUND the white spot that indicates fertility. However the USDA says there is no way to tell by looking at the yolk that the egg is fertile. Not that I'm a-saying that the USDA has it all right all the time... At any rate, do a search for 'bullseye' and you'll find a thread or two or three where folks have posted pics of what to look for. I've read the posts and looked at my eggs and ?? Only way to know for sure is to incubate them and see if you get any development after a week.
I believe all eggs have the white spot on them. If they have a ring around the spot, kind of like a bulls eye, that is what you look at to see if it is fertilized or not. There is a good thread on here that shows pictures of fertilized and non- fertilized eggs. I will find it and post it on here. Here is the link. https://www.backyardchickens.com/forum/viewtopic.php?id=16008