SUGGESTIONS FOR THE STUDENT 97 
Describe condition of a Passerine bird at birth and its subsequent 
plumages and molts. About how long is it in the nest? How long does it 
wear the juvenal plumage? What plumage follows? What feathers are 
usually retained at the postjuvenal molt? When does the prenuptial molt 
occur? Is it usually complete? What molt is complete? How does the 
natal down of precocial birds differ from that of altricial birds? How long 
do some Snipe wear the postjuvenal plumage? What variation in the law 
of molt is shown by Ptarmigan and most swimming birds? Describe changes 
in color due to wear or fading. Give illustrations of the acquisition by molt 
of nuptial plumes. Describe differences in color due to age. When do most 
birds acquire their mature plumage? Mention several species which do not 
reach full plumage until at least their second year. Describe the plumage 
changes of the Scarlet Tanager, American Goldfinch, and Bobolink. When 
the adults are unlike in color, which is usually the brighter? Which parent 
does the nestling usually resemble? What may be inferred from the spotted 
juvenal plumage of the Bluebird? What is Darwin’s theory of sexual se- 
lection? What is Wallace’ s theory? Describe what is meant by secondary 
sexual characters and give cases in illustration. What relations exist be- 
tween the degree of intensity of a bird’s color and the climatic conditions 
under which it lives? Describe the case of the Song Sparrows. Is it believed 
that their changes in color are due to the direct influence of environment 
rather than to the influence of natural selection in establishing protective 
colors? Why are concealing colors necessary? To what factors other than 
color may a bird owe its comparative immunity from its foes? Are they 
required by all species? How may we account for the wide range of color 
in arboreal birds? What is Thayer’s principle of counter-shading? Demon- 
strate this theory with the aid of decoys. What are ‘obliterative’ markings? 
What are ‘banner’ or ‘directive’ marks? What theories have been advanced 
to account for their significance? Mention all the birds you know which 
reveal white marks in flight. Whatis albinism? melanism? xanthrochroism? 
erythrism? Describe an albino which you have seen. Did it act like normally 
colored birds of its own species? What may be learned from observing 
albinoes or other birds so marked that they may be recognized? Have you 
ever known a caged-bird to change in color? 
REFERENCES 
1871. Darwin, C., The Descent of Man, Chaps. XIII-XVI.—1877. 
Auten, J. A., The Influence of Physical Conditions on the Genesis of Species, 
Radical Review, I, pp. 108-140. Reprinted in Smithsonian Rep. 1905, pp. 
375—-402.—1891. Wauuace, A. R., Darwinism, Chaps. VIII-XI, (Macmil- 
lan).—1890. Poutron, E. B., The Colours of Animals, (Appleton).—1893. 
Newton and Gapow, Colors of Birds, in Dictionary of Birds, (Macmillan). 
—1896. Sronsz, W., The Molting of Birds, Proc. Acad. Nat. Sci., Phila., pp. 
108-167.—1900. Dwient, J., Jr., Sequence of Plumages and Moults of the 
Passerine Birds of New York, Annals, Acad. Sci., XIII, pp. 73-360. See also 
Auk, XVII, pp. 34, 143, 368.—1907. Brrsr, C. W., Geographic Variation 
in Birds with Especial Reference to the Effects of Humidity, Zodlogica, I, 
pp. 1-41.— 1908. Berne, C. W., Seasonal Changes of Color in Birds, Am. 
Nat., XLII, pp. 34-38.—1909. THaynr, G. H., Concealing Coloration in 
the Animal Kingdom, 4to., 260 pp., ills, (Macmillan).—1910. Tracy, 
H. C., Significance of White Markings in Birds of the Order Passeriformes, 
Univ. Cal. Pub. in Zodél., VI, pp. 285-312.—1910. Pycrart, W. P., A His- 
_ tory of Birds, (London: Methuen & Co.).—1911. Barsoovr, T., and Pxit- 
ups, J. C., Concealing Coloration Again, Auk, XXVIII, 179-188.—1911. 
THAYER, A. H., Concealing Coloration, Pop. Sci. Monthly, July, pp. 20-35. 
—1911. RoosevEtt, Turopore, Revealing and See oma Coloration in 
Birds and Mammals, Bull. Am. Mus. Nat. His., XXX, pp. 119-231. 
