OF NORTHERN ILLINOIS. 511 



intensity ; favoring the idea also that the extreme examples in either case are the results 

 of extremes in age, the mean or ordinary really, of course, being alone typical. But there 

 are exceptional examples of birds unmistakably very young and very pale in color, that 

 have the rufous suffusions at a minimum ; which tends to show that the variation is by no 

 means to be wholly accouuted for on the theory of differences in age. 



The difference in distribution once considered to exist between the species of the first and 

 second groups, the second having been considered the western representatives of the first, 

 especially in the case of T. nanus Aud., and T. ustulatus Nutt., described originally from the 

 Columbia River, 1 does not appear to really exist, since specimens which are exact counter- 

 parts of the western occur in the Atlantic States. 



Another point not unlikely to be urged as a valid distinction, is the supposed differ- 

 ence in the breeding habits, and in the color of the eggs of T. "nanus" and T. "ustulatus" 

 on the one hand, and of T. Pallasi and T. fusccsccns on the other, the two latter laying un- 

 spotted deep-green eggs, and nesting on the ground, while the two former nest in trees a 

 few feet from the ground, and lay pale-green eggs, speckled more or less thickly with pale 

 rufous. But in this connection two things are to be noticed : first, the remarkably close re- 

 semblance of both the nests and the eggs of T. " nanus " and T. " ustulatus" as well as of T. 

 "Alicice," to those of T. Swainsoni ; second, that these nests all come from places where T. 

 Swainsoni is known to breed. 



In two nests, labelled respectively " T. Swainsoni" and " T. ustulatus" presented by the 

 Smithsonian Institution to the Museum of Comparative Zoology, the resemblances are as 

 close in the materials, which are quite peculiar, of which the nests are composed, and in the 

 color and markings of the eggs, as we often find in two nests and their eggs of different in- 

 dividuals of the same species. In all of the several sets of eggs of T. " nanus " and T. "ustu- 

 latus" I have seen, there is the same close resemblance in all cases to those of T. Swainsoni, 

 while on the other hand they differ widely from those of their much nearer allies, T. Pallasi 

 and T. fusccscens. So there appear to be strong grounds for suspecting they are all really 

 nests and eggs of T. Swainsoni; the strong general resemblances between the dark olivaceous 

 stages of plumage of the three species ( T. Pallasi, T. fuscescens, and T. Swainsoni) being very 

 likely to mislead collectors. 



As pertinent to the subject, we add a few observations on the value of certain characters 

 generally considered among birds as specific, as, particularly, the proportions of the pri- 

 mary quills, and the size of different parts. The relative lengths of the primary quills, so 

 commonly dwelt upon even now as affording distinctive specific characters, are really vari- 

 able and hence, artificial characters. Besides their having a greater or less range of 

 variation in mature birds of the same sex, they also vary with age. The general form 

 of the wing seems to be a generic rather than a specific character, and is, besides, from an 

 embryological point of view, often an important guide to the relative rank of genera in their 

 respective families. In examining very young nestlings, we find that the quills in most 

 birds, and always in the true Oscines, all appear in sight at once, and that at first the} - are 

 so nearly alike that it is impossible to say which is the longer or thicker, or what, judging 

 from this stage alone, is to be the ultimate form of the fore-wing. Very soon, however, a 

 change begins, and those primaries eventually to be the longest, whether the first and 



1 The first specimen of T. " ?ianus " Audubon ever saw, however, we are led from his remarks to believe, was derived 

 from Pennsylvania. See Orn. Biog, vol. v, p. 201. 



