Hens lay special eggs at times. There is the very first egg they lay, which is a tiny egg. There is the first egg they lay after their winter lull. These eggs also tend to be smaller. And then there is the first egg they lay after raising chicks. And today this mother laid her first egg after raising chicks for three weeks. That is on the early side. Most hens take more than a month before they go back to laying eggs.
I get the sense that this mother may not be raising her chicks much longer. They are getting very independent and at times during the day they stray tens of feet from her. When she was up on the nest laying her egg, her five chicks huddled together and waited patiently for her to come back down.
