552 THE AMERICAN NATURALIST [Vol. XLYIII 



Thus in the case of the terns, the black-capped chickadee, 

 the black-crowned night heron, and other birds, a black 

 crown patch is noticeably marked off. 



The Ear Patches. — The ear patches in birds are small, 

 yet often specially marked out by white boundaries, which 

 are permanent parts of the pattern. Yet there is 

 doubt but that the acquisition of such white boundar 

 is a derived character. It is common for the ear patches 

 to be colored differently from the surrounding parts, 

 forming as in some species of tanagers a black auricular 

 area contrasted with the blue of the head and neck. Of 

 particular interest in the present connection, however, 

 are those cases in which a pigmented ear patch is more 

 or less clearly marked off by a white line above it i 

 below, or both. The superciliary stripe, so common in 

 birds, is of course a development of a primary break 

 above the patch, separating it from the crown patch. 

 Where the stripe is narrow it is hard to say which patch 

 has begun to be restricted, though often no doubt both 

 are more or less involved. Thus the Garganey teal has 

 a very wide white eye stripe, and in other species of 

 ducks the whole side of the head may be white, indicating 

 much greater restriction of pigment formation in con- 

 tiguous patches. A beautiful example of the develop- 

 ment of a white stripe at the lower border of the ear 

 patches is found in the Inca tern, in which a line of white 

 feathers runs from just above the gape along the lower 

 side of the auricular patch and separates it from the 

 dark throat. But not only is the white line developed, 

 but the feather- composing it are specially elongated and 

 recurved, as if the mark were one of particular decora- 

 tiveness. The dark ear patch is noticeable in many 

 hawks, separated above and below by white areas, as in 

 the duck hawk and the osprey, though differing in the 

 size of the white areas. 



An instance in which the white line separating the 

 crown patch from the ear patch, is even now in course of 

 becoming established as part of the permanent pattern, 



