Natal plumages and downy pteryloses of passerine birds of North America. Bulletin of the AMNH ; v. 113, article 5

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New York : [American Museum of Natural History]
"Natal-down pterylae consist of definitely arranged rows of neossoptiles superimposed on certain presumptive contour-feather pterylae. Neossoptiles are essentially only modified downy tips of certain teleoptile feathers; thus the natal plumage is only a transitory phase of the juvenile plumage. Reduction of the natal plumage is considered to be a product of specialization, but it is here proposed that reduction is a by-product of total embryonic specialization. Complete loss of the natal plumage has occurred independently in some members of several families: Hirundinidae, Corvidae, Chamaeidae, Bombycillidae, Vireonidae, Parulidae, Ploceidae; possibly in Paridae and Sylviidae; and perhaps in others, notably Troglodytidae and Laniidae. Gradual definite reduction has resulted in generally similar natal-down pteryloses in members of any given taxonomic unit. There is some individual variation within the species in natal plumage, usually involving the number of neossoptiles in given tracts, but rarely in the presence or absence of tracts themselves. Because of the fragility of the natal plumage, most variations observed are due to abrasion rather than to genetic differences. Observations on the colors of natal plumages show this character to be the least trustworthy for comparative analysis. Color characteristics vary considerably as a result of fading, soiling, and abrasion. Head-tract down is often darker than down elsewhere. Though post-natal growth of neossoptiles has been credited to some species my measurements seemed to indicate that the natal down completes its elongation before the time of hatching. Post-embryonic down growth might be referable to the Heinroths' 'Pelzdaunenkleid.' The adaptive relationships (if they exist) of down color, distribution, and structure with temperature, illumination, and concealment have yet to be functionally demonstrated. There is admittedly a tendency for over-all reduction or complete disappearance of natal down correlated with enclosed types of nidification. In domestic canaries there is probably a genetic relationship between color of teleoptiles and length of neossoptiles. The distribution of neossoptiles, their number per pteryla, and the length of neossoptiles are amenable to quantitative analysis and thus provide a needed quantitative tool for the delimitation of genera and families and for the interpretation of possible phylogenetic relationships. Deviations in direction and magnitude from the basic pterylological plan of each family should provide a quantitative measure of adaptation. In passerines, the average total number of neossoptiles per species is 130 (151 if we exclude the naked species); the average total aggregate is 945 mm. (1096 mm. if we exclude the naked species) as determined by these data. Tentative familial and generic synopses were prepared with the material at hand. Some of the Tyrannidae had the greatest number of neossoptiles and downy regions found among the passerines, which differentiate that family clearly from all the others. A previously undescribed auricular ring in Sayornis was noted. Three groups of swallows were segregated similarly according to the manner of nesting. Hirundo and Petrochelidon showed allied characters. In the Corvidae there appeared a tendency for parallelism towards nakedness. The genus Baeolophus was indicated as possibly still usefully expressive of relationships in the Paridae. The Sittidae, Paridae, and Certhidae had a comparable degree of down reduction but are no more similar to one another in pattern than they are to the Troglodytidae or Parulidae. Desert wrens and thrashers seem to have relatively greater down aggregates than species from less arid environments. The members of the Mimidae and Turdidae that were examined were characterized generically by natal-down pteryloses. Sturnus vulgaris, with its large quantity of down, presented one of several exceptions to alleged correlations of nudity and cavity nesting. The Vireonidae had down of greater fragility than that of other families. Disparity in neossoptile number and aggregate between Seiurus aurocapillus and S. noveborecensis is thought provacative. The Icteridae and Fringillidae showed many similarities. Molothrus ater, in spite of its social parasitism, retains the typical natal-down pterylosis of its family. Cardueline finches were consistently white downed. In Spizella differences of down aggregate (but not of distribution) from species to species showed interesting amplitude in a currently recognized genus. Statistical treatment of two species showed the positive value of natal pterylosis as a tool in systematics even with small samples. A hypothesis was proposed, that natal-plumage characters are probably not so much selected for as such as they are modified passively by linkage with changing embryonic sequential patterns in evolution. Absence of correlation between length and number of neossoptiles from species to species favored a direct genetic control of neossoptiles rather than a hormonal control. Of the major pterylae the following five neossoptile regions were the most constantly present: rniddorsal, coronal, occipital, scapular, and femoral. Ventral, crural, rectrix, and alar tracts were lost most often in evolution. The more generalized neossoptile pteryloses of a species with an adult ephippial apterium in species with specialized neossoptile pteryloses suggest that the ephippial space is a primitive character in passerines"--P. 429.
p. 343-436, [2] p. of plates : ill. ; 27 cm.
Thesis (M.A.)--Clark University.
Includes bibliographical references (p. 431-436).