What causes a stunted growth?

[as110]

I have 4 chicks hatched 1 week apart. The first one is huge, she always was. The second one hatched a week later and she didn’t grow at the same rate as the first. One week later another hatched, so now I could tell what a huge difference these birds have. The third one caught up to the second one in size and it looks like he will outgrow her. The last one hatched 4 days after the third and she is growing well.

The chick in question has feathers on her back sticking up and she looks scruffy. A few weeks ago I thought she was sitting like a pinguin. But when they are out of the crate they play, fly, eat and scratch, chase each other and do normal chicken things. They sleep on the perch.

They have never been outside or near other hens so disease or mites are 0% chance. They are in the house on a cabinet.
They are on organic starter feed.

Any ideas?

Here are some pictures to show how they progressed. The size difference is big. The last 3 are more uniform in size wven though they are 1-2 weeks apart. I thought the first one was not normal with the fast growth but I can see now after all these weeks that the second one is stunted. Everyone is visibly growing but the difference between 1st ans 2nd is growing bigger.

 

[PirateGirl]

Are you sure the chicks all have the same mother AND father? Genetics could play a role. The one with feathers sticking up as you said, appears to have inherited the frizzle gene. Do a little google image search of frizzle chickens and you will see that this is something that is just normal for some birds. This bird will always have feathers like this.

 

[as110]

Are you sure the chicks all have the same mother AND father? Genetics could play a role. The one with feathers sticking up as you said, appears to have inherited the frizzle gene. Do a little google image search of frizzle chickens and you will see that this is something that is just normal for some birds. This bird will always have feathers like this.

I am pretty sure they don’t have the same mother and father. I know they came out of the ameraucana eggs. I have an araucana rooster and a laced wyandotte rooster. I don’t have any fancy fluffy bird. It’s ok if that is what she inherited.
But why is her growth so much slower than everyone elses?

 

[PirateGirl]

Well, having different fathers could certainly explain size differences.

 

[as110]

I don’t have a picture of the white rooster but he is the same size.

The last two chicks are from the jersey giant hens so they might get bigger than the rest.