The nestlings will be 2 weeks old this week. Viewers have noticed quite a size difference between the first 3 hatched and the last to hatch. In most birds of prey, including peregrines, the females are larger than the males. It is very possible that in this nest, the first 3 to hatch are female and the last to hatch is a male. The difference in sex and the few days difference in when the eggs hatched could account for the marked difference. The bulge under their chins are full crops. Their skin is gray and with only a few feathers, once the crop is full and expands to show bare skin, it really can look strange!
They are also beginning to get mobile and over the weekend, walked over to in front of the camera giving a close up view.
Here's a nice video of a feeding that shows how the smallest chick maneuvered into a better position to get fed, too. And, as discussed last post, the inside of the nest box continues to get very messy...