Blog #399 Fantastic Feathers
Orpheus skims the water for a drink and to wash, courtesy of Cynthia Sedlacek.
At five weeks old, the Salt Point Three have finished their exponential growth spurts and are putting on muscles and their final feathers. Despite their new ability to thermoregulate, the nestlings still lounge in the shade provided by Ursula as their “mombrella.” The nestlings’ tender skin is sensitive to UV rays exposure, and Ursula does her best to keep them cool in the hot summer sun. Ursula will take quick dips in the creek or lake to further cool off the young. Ospreys get their drinking water from the fish they eat although, once they can fly, they may sip water from the lake or creek. The young birds have fully developed crops now, which are the first chambers of their two-section stomach, where food is digested. When satiated, the crop will bulge.
From their second-week-old onward, feathers start replacing down. First to grow are the rusty-yellow pinfeathers on the head and neck followed by dark body feathers. Their feathers slowly push the down out of the feather sheaths, which grow from follicles arranged in neat rows called feather tracts. In between the feather, tracts are patches of bare skin that will get covered by a thick growth of feathers. The arrangement of feathers allows the birds to function with fewer feathers overall, like the shingles on a roof, which drastically reduces the total weight of feathers—one of many adaptations for flight.
Feather track on a bird. The uropygial or preen gland waterproofs the feathers, from Flicker.
Growing feathers is an itchy process, especially on hot humid days, but preening brings temporary relief. The older the nestlings get, the more they will preen to relieve the itch. Blood vessels nourish the feather growing in the feather sheath until it is fully formed, then the blood vessels wither away. Once the feather is fully formed, the waxy sheath bursts open and falls off, or the bird removes the sheath while preening, and the feathers unfurl from their packaging.
Emerging dark feathers. Ospreys preen and peck away at the white sheaths until they crumble.
Feathers are complicated structures vital to the lives of Ospreys. Feathers are some of the lightest yet strongest materials in nature. Flight feathers, critical to the Osprey’s existence, are extra strong. Feathers can withstand raging winds, rain, snow, intense sunlight, and collisions with tree branches. They are flexible too: a bent feather shaft will straighten.
Remarkable feathers enable this female Osprey to fly and fish, courtesy of Cynthia Sedlacek.
Much goes into making the complicated interwoven structure of a feather, but they are not meant to last forever. The wing and tail feathers grow quickly and will be complete within a few weeks. The young bird keeps these feathers for over a year, at which point they are replaced during a process called molting. Flying and fishing are learning processes, and young Ospreys commonly bump into objects, damaging their feathers. It is thought that the softer feathers of immature Ospreys cushion the impacts of crashes, tumbles, and minor collisions.
When looking at the Salt Point Osprey Nest Cam footage, you can differentiate the chicks by their growing barred tail feathers. Moana’s tail is coming in the fastest, and the size of the barring is growing. Lani’s tail is a much smaller, buff-colored bar at the moment. Makai’s tail is somewhere between the two extremes. Using the tail to determine the relative age of the chicks will hold for the next few weeks until their tails are complete. Their wing feathers are also filling out quickly. Every day, subtle changes in their feathers can be seen. All three have a rusty wash on the nape of their necks. Dark contour feathers with buff-colored tips are emerging from their waxy sheaths creating a brindled pattern on their backs and causing them to frequently preen and scratch. Moana, as indicated by her plumage, is by far the most mature of the nestlings with the others not far behind. Lani is catching up to the others and beginning to resemble Makani.
Ursula and the Salt Point Three at four weeks of age, courtesy of Cynthia Sedlacek.
An Osprey, like other birds, can move each of its feathers independently, using tiny muscles in the skin. This helps a bird place its wing feathers, for example, into position to make a turn or slow down. The Ospreys can also raise and lower the feathers on the nape of their necks.
Osprey feathers are either varying shades of brown and white or all white on the breast and belly. The Osprey’s brown feathers are colored by melanin, which is made within their body. Melanin absorbs certain wavelengths of light and reflects the rest. Humans see the reflected light as shades of brown. The white feathers lack all pigment.
A variety of feathers cover an Osprey’s body, which all look different and are modified to serve certain functions. The fluffy down feathers trap warm air, insulating the bird from cold and heat. They are fluffy because they lack the barbules needed for a smooth surface. The contour feathers give the Osprey its aerodynamic shape reducing drag while in flight. Flight feathers are the largest, most substantial, and most impressive of the contour feathers. They vary widely in shape across the bird's body from the primary and secondary wing feathers to the tail feathers.
Adult Ospreys replace or molt all their feathers yearly although it takes young birds a bit longer. The prominent flight feathers on the wings are the ten primaries, which grow from the wrist to the wing tip, numbered Primary 1–10 or P1–10, and the ten secondaries (S1–10) starting at the wrist and progressing inwards toward the body. Another tract of feathers called the tertiaries are between the secondaries and the body. The primaries come in many shapes and sizes adapted for optimum aerodynamics of flight.
Feathers on an adult female Osprey, courtesy of Montana Osprey Cams.
The 12 colorful tail feathers called rectrices are numbered starting from the middle of the tail (rectrices 1 or R1), and working to both the right (R1–R6) and left (R1–L6) side of the tail. These feathers often get battered as the tail is used for a rudder and breaks in the air and underwater. The buff edges on the juvenile feathers are weaker and more easily damaged without impacting the functioning of the feather and the flight of the bird.
The golden manes of the nestlings grow in first, courtesy of Cynthia Sedlacek.
Ospreys of all ages spend a lot of time preening, combing their feathers into place, removing ectoparasites, and spreading waterproofing uropygial oils on them. Now that the chicks have started preening, it’s a bit like a toddler teething. The chicks start preening as their feathers begin to emerge, which is presumably a pretty itchy process. Once their feathers are out of their sheaths, they will spend a lot of pushing, brushing, and running their beaks through their new feathers to keep them in good condition for flight.
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