100 BULLETIN OF THE 



ings largest and brightest. A wide range of variation in this respect is 

 seen in all birds which have the breast and lower plumage marked with 

 dark streaks and spots on a lighter ground, or that have the whole plu- 

 mage streaked. In the common song sparrow (Mcluspiza melodia), the 

 fox-colored sparrow (Passerella iliaca), the swamp sparrow {Mclospiza 

 palustris), the black and white creeper (Mniotilta varia), the water wag- 

 tail (Seiurus noveboracensis), in Tardus fuscescens and its allies, etc., 

 the difference in the size of the streaks is often very considerable. In 

 the song sparrow they vary to such an extent that in some cases* they 

 are reduced to narrow lines ; in others so enlarged as to cover the 

 greater part of the breast and sides of the body, sometimes uniting on 

 the middle of the breast into a nearly continuous patch. Variation in 

 this respect is equally great in the fox-colored sparrow and in the grass 

 finch (Pooccetes gramineus). Massachusetts specimens of the savanna 

 sparrow {Passerculus savanna auct.) also present variations exactly par- 

 allel with those of the song sparrow. Yet these differences, with other 

 variations to be hereafter mentioned,! have been regarded, as in the 

 case of Passerculus savanna, as of specific value. Similar variations in 

 the Ilijlocichla group are very marked, as in Turdus (Hylociclda) fus- 

 cescens especially. In some specimens of this species the colors are on 

 all parts not only very pale, but the markings on the breast are reduced 

 to indistinct narrow lines ; in others, in which the general color of the 

 plumage is darker, the markings on the breast are dark, broad, and 

 triangular. Two specimens taken in Cambridge the same day (early 

 in May), both of which are males, exhibit these extremes. Average 

 male specimens of the black and white creeper (Mniotilta varia), in 

 which the plumage is varied with longitudinal black and white streaks, 

 have the black streaks about a third broader than the white ones ; 

 but other specimens occur in which the white ones are equal to and 

 even broader than the black ones ; others have the black streaks so 

 much broader than they usually are, — the white ones of course being 

 proportionally reduced, — that the general aspect of the plumage at a 

 short distance is nearly black. The difference between these two 

 extremes is strikingly great. Yet similar variations, scarcely less in 

 degree, occur in nearly all of the striped-breasted warblers. 



In birds which have 'lie ground color of certain areas of the body 



* Perfectly mature specimens only are here referred to. 

 | See the remarks on the genus Passerculus in Part IV. 



