Black Jersey Giant growth rate

[SarahFair]

I got some white rock chicks at 3 weeks of age one week and the next week got some 4 week old Jersey Giants. The White rocks have all feathered out and have been running with the others for weeks. My Giants have still not feathered out on their heads and are much smaller than the rocks.

I know that Giants mature slower but at this eary a stage?
They are about 7 weeks

I bought my first 2 chickens, barred rocks, at 8 weeks and they were MUCH larger than either of these.