90 



ALTRICIAL GRALLATORES — HERODIONES. 



Lkckish. Young: Uniform, rather dark, grayish brown, the rump, upper tail-coverts, basal half 

 of tail, anil entire lower i)arts, including axillars and lining of the wing, continuous white ; head 

 and neck streaked with dusky or giayish brown on a grayish or dull whitish ground-color. 

 Feathering of the head extending forward almost to the bill.^ 



Length, about 24.0(1-2R.0n ; expanse, about 40.00 ; wing, 10..30-11.75 ; tail, 4.00-5.00 ; culmen, 

 4.15-6.3U ; depth of bill, .()0-.72 ; tarsus, 3.10-4.00 ; middle toe, 2.15-2.70 ; bare portion of tibia, 

 2.00-2.80. 



In this species there is a range of individual variation not exceeded by any member of the 

 family ; this variation afl'ecting not only size and relative i^roportions of the different parts, but 

 also characters which have been accorded generic or subgeneric value. Thus, taking two perfectly 

 adult birds from localities geographically near together (Mazatlan and Tehuantepec, Western and 

 Southwestern Mexico), they represent very nearly, if not i^uite, the extremes of size, especially 

 as regards the bill ; one of them (No. 58816, Mazatlan) having this member 6.30 inches in length, 

 while in the other (No. 59773, $ , Tehuantepec) it measures only 4.70. As to colors, they are 

 identical, both being pure white, with the terminal portion of the four outer primaries glossy 

 greenish-black. Tliei-e is a most remarkable difference, however, between these two examples in 

 tlie anterior outline of the feathering of the head, which difference may be explained as follows: 

 In the Mazatlan specimen the frontal apex all but comes in contact with the base of the culmen, 

 there being left between a space only about .05 of an inch wide; in the Tehuantepec specimen there 

 is an interval left of .80 of an inch ! In the Mazatlan example, the anterior feathei-s of the throat 

 i'(irm a broad angle projecting forward into the bare gular skin for a distance of .60 of an inch ; in 

 the Tehuantepec specimen, their anterior outline has exactly the opposite form, being regularly and 

 deeply concave, so that the bare gular skin has a semicircular or regularly convex posterior outline — 

 exactly as in fully adult specimens of E. ruber ! In the former of these specimens the malar 

 feathers extend forward to within .25 of an inch of the rictus, or to much beyond the anterior 

 angle of the eye ; while in the other they approach to within only about .70 of the rictus, scarcely 

 reaching to below the middle of the eyes. 



Other characters in which the Tehuantepec examjile differ-; from the one from ]\Iazatlan, consist 

 in the subterminal portion of the bill being black for the space of nearly two inches, and in the 

 distinct serration of the middle portion of the tomia. These extremes of A'ariation are noticeable 

 among skins obtained during the breeding season in Florida, specimens from the same breeding 

 grounds differing as much as the two described above. 



Immature specimens show, according to age, all possible stages of plumage intermediate be- 

 tween the pure white adult and gray young. 



The ^\^lite Ibis is a resident only in the more southern portions of the United 

 States, though it not unfrequently occurs as a straggler in various places farther 



* According to Audubon, "the young birds are at iirst covered with thick down of a dark gray 

 color." 



