THE BLACK-BILLED CUCKOO. 31 



a fallen limb, the top of which was resting upon underbrush. As an exception 

 to their low nesting, I once found a nest containing two well-feathered young 

 and two fresh eggs over 18 feet from the ground, placed in the top of a cedar 

 tree, in a dense thicket of other cedars." 



Both sexes assist in incubation as well as in the care of the young; they 

 appear to be devoted parents, and the fact that they are occasionally willing to 

 abandon their young to the mercy of foster parents appears rather unaccount- 

 able, to say the least, especially when it is positively known that they occasionally 

 remove their eggs, as well as the young, from one nest to another in order to 

 better protect them from possible harm. In my opinion, the real causes for the 

 so utterly inconsistent behavior on the part of some of these birds are not yet 

 fully understood. 



The number of eggs laid to a set varies from two to seven; sets of three or 

 four are most common, and those of over five are rare. Dr. Louis B. Bishop found 

 a set of seven eggs of this species near New Haven, Connecticut, on June 7, 

 1893, in which three eggs were fresh, in two incubation had just begun, in 

 another it was somewhat more advanced, and in one egg the embryo was well 

 formed. There is frequently considerable difference in size among the eggs 

 found in the same set, although apparently laid by the same bird. In a set of 

 three eggs, for instance. No. 26019, United States National Museum collection, 

 taken by Mr. Thad. Surber, near White Sulphur Springs, West Virginia, on 

 June 3, 1893, the measurements are as follows: 26.92 by 20.07, 24.89 by 19.81, 

 and 22.35 by 18.54 millimetres, or 1.06 by 0.79, 0.98 by 0.78, and 0.88 by 

 0.73 inches; the difference is, of course, not always so great, but is often quite 

 perceptible. The eggs of the Black-billed Cuckoo are more nearly oval than 

 elliptical oval, and shorter and rounder than those of the Yellow-billed Cuckoo, 

 and much more deeply colored. Like these, they are unspotted; the shell is thin 

 and fine grained, with little or no gloss. Their color is difficult to describe 

 exactly, varying from nile blue to pale beryl green, and occasionally the shell 

 shows a decidedly marbled appearance, caused by different shades running into 

 each other, an illustration of which is shown in PL 5, Fig. 3. Aside from their 

 deeper color, they are also readily distinguished from the eggs of the Yellow- 

 billed Cuckoo by their smaller size. 



The average measurement of forty-two specimens in the United States 

 National Museum collection is 27.23 by 20.53 millimetres, or about 1.07 by 0.81 

 inches. The largest egg of the series measm-es 29.97 by 22.86 millimetres, or 

 1.18 by 90 inches; the smallest, 22.35 by 18.54 millimetres, or 0.88 by 0.73 

 inch. 



The type specimen, No. 22444 (PI. 5, Fig. 3), a single egg, Bendire collec- 

 tion, was taken by the writer near Fort Custer, Montana, on June 25, 1885, and 

 is a very peculiarly colored specimen, while No. 26019 (PI. 5, Fig. 4), from a 

 set of three eggs, and taken by Mr. Thad. Surber, on June 3, 1893, near White 

 Sulphur Springs, West Vkginia, represents about an average egg of this species. 



