What Is Neossoptile? Understanding Baby Bird feathers

What Is Neossoptile? Understanding Characteristics and Development of Baby Bird Feathers

The plumage of newborn birds at hatching has down feathers called Neossoptiles. 

These Neossoptile ( Greek word meaning, neossos- young bird, ptile- comb form) may be either thickly or sparsely, distributed. Just after hatching,  they are pushed out from their follicles by the sheath (pin feathers) of the developing teleoptiles (contour or down feathers) to whose tips they are attached. 

Down feather Neossoptile: Diagram
 

Gradually the dislodged neossoptile disintegrates and disappears by the time the teleoptiles have completely unfolded. 

The first clothing of the newly hatched bird consists more of soft feathers on the whole, resembling the down feathers of the adults but with some distinguishing characters which make them different from the teleoptiles ( contour or down) which appear next.

Down feather 

Characteristics of Neossoptile

These characteristics make them soft and downy.

1. A very short calamus 
2. An insignificant or ill-defined rachis, if there be one at all.
3. Absence of Cilia
4. Long and slender rami.
5. Absence of an aftershaft except in Dromaeus.

Feather Development

Development of Down Feather Neossoptile: Diagram 
A- Dermal papilla forming feather papilla, B- Papilla sinking into a feather follicle, C- Feather germ elongates, D- Newly formed Neossoptile, Down feather Neossoptile,1-The germinating ring with a series of newly formed barbs, 2 and 3- Stages in development of rachis

The skin of the integument of birds and other vertebrates consists of dermis and epidermis. 

Dermis: It is the inner part and consists of the nutrient tissue carrying blood vessels. 

Epidermis: It is the outer part consisting of numerous cell layers. 

The innermost being stratum germinativum, which is the live layer proliferating continuously outward with newly formed cells.

The outermost layer, Stratum corneum are made of dead, horny material formed by the cells that become flattened and are force to outwards by the new cells from the stratum germinativum.

In the formation of a feather, the dermis becomes the pulp supplying nutrition and pigment material,

•  The stratum corneum forms the feather structure and the encasing sheath, the periderm.
• The stratum germinativum, forms a ring of cells (germinating ring), at the base of the feather, immediately surrounding the inferior umbilicus.

Both the scale and the feather start forming with a papilla which pushes up the overlying epidermis. 

Till this stage, their formation is similar. After this, if the papilla is destined to form a feather,  it becomes elongated and tabular; but if a scale is to result, it soon becomes flattened and plate-like.

Development of Neossoptile

The feather development starts about the fifth or sixth day of incubation, when the feather rises on the delicate and semi transparent skin of the embryo as tiny papillae called the dermal papilla from which feather will develop.

The papilla which is the pulp from where the feather develops, continues its out growth and at the same time sinks into a pit, i.e. the future feather follicle. 

Meanwhile, the  stratum corneum of the overlying  epidermis is produced by the outward proliferation of cells by the germinating ring around the base of the papilla,

• A series of columns (the future barbs), which run parallel from the ring to the tip of the papilla and are closely applied to the inner pulp. 
• An outer cone-shaped periderm.

As rapid growth occurs, the distal end of the papilla and its epidermal elements, soon project from the follicle above the surface of the skin as "pin feathers", the proximal end stays in the follicle as the calamus. 

Eventually,

• The pin feather splits beginning at the tip,
• the columns separate as barbs and extend freely, 
• and the underlying pulp disappears by resorption.

As the feather growth is completed the entire periderm above the follicle has disintegrated into a powdery material and the barbs have spread out from their base on the calamus, The pulp in the calamus has dried up and the inferior umbilicus no longer functions as an entrance for nutrition. 

Deep in the follicle, below the base of the calamus, there remains a small papilla that will give rise to the teleoptile (contour or down).

These Neossoptile provide excellent insulation and camouflage for young birds as required for their survival.