Siblings

Here are pictures taken exactly a year apart. Each shows a clutch of osprey chicks apparently from the same parents, hatched and fed at the same location. The first set hadn't fledged when we caught this picture. The second set have already fledged, causing me to speculate that the first clutch were hatched later in the season. This year's chicks just seem more mature.

Of course, I have a better lens this year but I don't think the lens can account for the more fully feathered, better muscled, and more amber eye color of this year's chicks. Anyone have a thought?