Lecture 14 Feathers

What are all feathers composed of

The protein beta-keratin in a basic branching plan. The calamus extends into the central rachis which branches into barbs and then into barbules with small hooks that interlock nearby barbules.

What are the two main types of feathers

1. Pennaceous

2. Plumulaceous

What are pennaceous feathers

Stiff mostly flat feathers used mainly as primary and secondary flight feathers. Microscopic hooks on the barbules interlock to form a wind and water barrier and for added strength. Most also have a fluffy plumulaceous region at the base where it attaches to the skin to add insulation

What are plumulaceous feathers

Downy feathers loosely arranged to provide a thick layer of insulation in areas where pennaceous feathers are lacking. They have flexible barbs and long barbules but no hooks on the barbules allowing them to spread out into a fluffy mass rather than forming a flat surface.

What are the seven feather types

1. Flight feathers—remiges

2. Tail feathers—rectrices

3. Contour feathers

4. Semiplume

5. Down

6. Filoplume

7. Bristle

Describe flight feathers/remiges

Specialized for flight with uniform windproof surfaces on either side of the central shaft formed by interlocking hooks. They are asymmetric with the shorter stiff side windward

What makes flight feather different from all other feathers

They attach directly to wing bones unlike all other feathers which attach to skin follicles

Describe tail feathers/rectrices

Most feature an interlocking microstructure similar to wing feathers. They are arranged in a fan shape to support precision steering in flight. Most have six pairs on the tail. They are symmetrical in shape at the midpoint of the tail and become more asymmetric near the edge—some used as showy ornaments

Describe contour feathers

They cover the body and parts of wings for streamlining. Mostly symmetrical, arranged in overlapping patterns like shingles and have waterproof tips with fluffy bases tucked close to the body. Can help attract mates or camouflage

What are coverts

Contour feathers on the wing that help shape the wind into an efficient airfoil by smoothing over the region where the flight feathers attach to the bone

Describe semiplume feathers

They are plumulaceous, mostly hidden under other feathers and have a central rachis but no hooks on the barbules so they make a fluffy insulating layer

Describe down feathers

Very plumulaceous with even looser branching structure than semiplumes and little to no central rachis. Relatively short and close to the body to trap heat

Describe filoplume feathers

Short simple feathers with few barbs. They function like the sensory whiskers of mammals.

Describe bristle feathers

Simplest feathers with a stiff rachis that usually lacks barb branches. Most commonly found on the head, may function like eyelashes

What are pigments

Molecules found in both plants and animals which can be deposited into the feather matrix as it grows. Three main groups

1. carotenoids

2. melanins

3. porphyrines

What are carotenoids

Type of pigment produced by plants usually acquired by eating things that have eaten plants like insects. Produces bright yellows, oranges and even reds.

What are melanins

Pigments occurring as tiny granules of color in both the skin and feathers of birds. Also provide strength and resistance to wear and tear so many white birds have black feathers on their wings or wingtips to protect them

What are porphyrins

Pigments metabolically produced by modifying amino acids. Different chemical structure in each porphyrin but they all fluoresce bright red when exposed to UV light and produce a range of colors in visible light.

Example of porphyrin

The red pigments found in the wings of turacos which are a form of Turacin, produced by metabolism and rich in copper from diet of plants and fruit.

What are structural colors

Colors that are not generated by pigments but produced when light is refracted by the protein structure of feathers

How do iridescent feathers work

Its a structural color produced when light refracts off the microscopic structure of the feather barbules. Splits light into different colors depending on the viewing angle

How do non-iridescent feathers work

Its a structural color where tiny air pockets in the barbs of feathers can scatter incoming light causing a specific color—Tindell effect. Blue colors are almost always made like this

How do ultraviolet feathers work

Its a structural color where they reflect light in the UV range. Most birds can see this as most can discriminate a greater range of colors than humans

Explain the functional significance of feather replacement (moult)

Reproduction comes with costs which mediates a trade-off between current reproduction and survival. Birds grow and replace their feathers annually due to wear and tear and this is physiologically demanding so separating it from breeding is important

How does feather quality change with span of breeding

Birds that thought fall was quickly approaching and had to moult quickly so the feathers were grown faster had weaker feathers that were less insulating.