BIO 554/754
Lab 2 - Feathers, feather tracts, and molt of the plumage


 inferior umbilicus
 superior umbilicus
 vanes (inner & outer)

 powder down
 neossoptiles (natal down)

 secondary remiges
 alula feathers

PTERYLOSIS (see below)

 capital tract
 dorsal (or spinal) tract
 scapulohumeral (or humeral) tract
 femoral tract
 crural tract
 caudal tract
 alar tract
 ventral tract

Drawing of a duck plus drawings showing feather structure

Drawing of a feather

Fantastic feathers: form and function

How do feathers grow

Why are birds different colors?

Diagrrams of different types of feathers
Source: Prum and Brush 2003

Electron micrograph of a feather
Image source:



Numbers of feathers (from Chaplin, S. and J. Faaborg. 1988. Laboratory Manual and Field Exercises. Ornithology: An Ecological Approach. Prentice-Hall, Inc., Englewood Cliffs, NJ):

Feather tracts:

Although the shape and distribution of pterylae vary among different families and orders of birds, eight major pterylae or feather tracts can generally be identified. These include the: (1) alar tract, including primary and secondary flight feathers plus coverts, (2) caudal tract that includes the rectrices and coverts, (3) capital tract, including all feathers on the head, (4) spinal tract (or dorsal) that extends along the mid-dorsal line and includes the cervical, interscapular, dorsal, and pelvic regions; see Figures below), (5) humeral tract that extends from where the leading edge of the wing meets the body over the dorsal surface to the trailing edge of the wing, (6) femoral tract located on the dorsal surface of the thigh, (7) crural tract located on the lower leg, and (8) ventral tract that includes cervical, sternal, and abdominal regions (see Figures below). The presence of pterylae and apteria, and differences among birds in their shape and distribution, may (1) be adaptations for reducing the total weight of the feathering, (2) better accommodate the movements of the body and the feathers, and (3) aid in thermoregulation via loss of body heat from apteria (Stettenheim 2000).

Drawings showing the different types of feathers
Drawing of a contour feather

Drawing of feather barbs

Drawing of a bird's wing showing different feather categories

Drawing of a bristle featherDrawing of a filoplumeDrawing of a down featherDrawing of a semiplume

Photo of an America Bittern showing powder down feathers

While most other birds' feathers produce a small amount of powder, powder feathers
(yellow feathers near the bottom of the photo that form a "V") are highly developed in herons,
egrets, & bitterns and the quill of the powder down is continuously growing and disintegrating, thus
creating the powdery substance.  The barbs of powder feathers disintegrate, providing a fine powder that is
thought to aid in preening and waterproofing the other feathers. They are the only feathers that grow continuously
and are never molted. While many species have powder feathers scattered within patches of normal down, they are
most prominent in the herons and bitterns (family Ardeidae), and are located on the breast and belly.

(Source: The Bird Banding Program at Powdermill Nature Reserve)

Drawings showing the different feather tracts of birds

Drawing showing bird feather tracts
Pterylae and apteria of a Clark’s Nutcracker (Nucifraga columbiana), dorsal view (From: Mewaldt 1958).


Drawing showing bird feather tracts on the ventral surface
Pterylae and apteria of a Clark’s Nutcracker (Nucifraga columbiana), ventral view (From: Mewaldt 1958).

Literature cited

Prum, R. O., and A. H. Brush 2003. Which came first, the feather or the bird? Scientific American 208: 84-93.

Mewaldt, L. R. 1958. Pterylography and natural and experimentally induced molt in Clark’s Nutcracker. Condor 60: 165-187.

Stettenheim, P. R. 2000. The integumentary morphology of modern birds – an overview. American Zoologist 40: 461-477.

Useful links:

The Story of Feathers

Feather biology

Feathers - Part I

Feather Structure - Cornell

Feather facts


Back to BIO 554/754 syllabus