Just why do some young birds bigger than their parents? Mike Toms explains
When newly fledged young are seen feeding alongside their parents, they can appear to be somewhat bigger. Structurally, they aren’t any larger, but their loosely textured plumage makes them seem so.
They may also carry greater fat reserves, though these are not noticeable in the field. Chicks grow remarkably quickly – a young blackcap will leave the nest just 12 days after hatching from its egg – so resources are targeted towards the most important body components.
While the wing feathers needed for flight are fully developed ahead of the chick leaving the nest, the contour feathers that cover the body are not, with only enough developed to provide a loose covering. This means that the contour feathers are less tightly aligned to the body, giving a false impression of size.
These feathers will be replaced when the youngster undergoes its first partial moult, which usually happens within a few weeks of leaving the nest.