Changing in front of our eyes!

Aside from the rapid increase in size, the biggest change we see in growing osprey chicks is the development of their feathers. By around the second week you will have noticed that the colour and structure of Bob 1’s feathers were markedly different from Bobby Bach’s, but they still bore little resemblance to those of Mum and Dad.

Three weeks to the day since Bob 1 hatched and it is getting harder to tell the difference between them. The youngest Bob has now lost all of his hatchling feathers, and they are all beginning to look more like ospreys every day!

When the chicks hatch they are covered in a fluffy, white down, designed only to keep them warm. This down offers no protection against the elements and is the reason they are brooded so attentively for the first few weeks. As tiny pin feathers started to develop, the chicks began to go bald, giving each Bob a drastic new look. 

The pin feathers around Bob's neck will eventually look like Mums'

Each new feather initially contains vessels to supply them with blood as they are growing; you may have heard them referred to as ‘blood feathers’ for this very reason. They are all encased in a protective sheath when they emerge from the skin, which eventually breaks down from the tip of the feather, unveiling the intricately formed 'vane'.

Here you can clearly see the casings surrounding each new tail feather

Even though their feathers are still growing and are yet to fully unfurl, the chicks are preening them, and will continue to do so for the rest of their lives. This behaviour is crucial to their survival, with the weatherproof and aerodynamic properties of the plumage both depleted if the feathers aren’t groomed to perfection.

How old?

Feathers, or feather-like structures, came into existence more than 150 million years ago. In 1861 a fossil from this time was found in Germany that transformed our understanding of how feathers, and flight, evolved. The fossilised creature they discovered was later named Archaeopteryx, and it is believed that this species was key in bridging the gap between reptiles and the very first birds. 

Archaeopteryx fossil found in Germany, 1861

It's all in the detail

The structure of each individual feather really is remarkable. All modern feathers have a central ‘rachis’, or stem, and from this branch the ‘barbs’, and then ‘barbules’.

The down feathers that the chicks were born with are ‘plumulaceous’, and the barbules of these feathers do not interlock. The loose arrangement traps air and provides excellent insulation; these are also present in adult birds and are located closest to the skin. In wing, contour and tail feathers, the barbs are arranged in a much more regular pattern. This is due to the presence of small hooks on the barbules which do interlock and give the feather a much more rigid structure. These are called ‘pennaceous’ feathers.

Fit for flight

The chicks will have their first full set of feathers by the time they are ready to fledge. Flight feathers are attached to the bones of the wing with ligaments, giving them stability at the base for taking to the air. Unlike the feathers in the tail that are used for steering, wing feathers are very asymmetrical, with a distinct leading edge that prevents them from twisting in flight.

Contour feathers across Glesni’s back - waterproof, warm and streamlined in flight...and excellent for the Mumbrella!

Over the coming weeks there will be no sign of slowing as our three chicks continue to grow. Their feathers will begin to fill out, and it will become increasingly harder to spot the reptilian ancestry that we can see so clearly today.