This is Michael Chamberlains data for GA, however, I have seen Alabamas and it is nearly identical. I have also discussed this with him personally and, according to his data, even though it notes "proportion of hens laying and incubating" the inference is that there are more hens incubating in around the 2nd and third weeks of April than any other time and there are more broods hatching around the 2nd and 3rd weeks of May than any other time.