60 U.S. NATIONAL MUSEUM BULLETIN 2 37 part i 



performing a song-flight in the air above her. Flying forth on a hori- 

 zontal course, the male would circle out from the summit of a tree, 

 with wings and tail spread, uttering an almost continuous song. 

 In the air for eight to ten seconds, he would then fly back, usually 

 to the perch just vacated. I have never seen this display before a 

 female coming more often than four minutes apart. Song-flights are 

 not restricted to the courtship period but also occur, although less 

 frequently, while the female is incubating." 



Nesting. — In his study of the breeding behavior of the black-headed 

 grosbeak, Weston (1947) writes: 



Nesting usually takes place in deciduous bushes and trees bordering streams. 

 Nests are built also in bushes or trees away from stream courses in gardens, 

 dense brushland, closed woods and parklands; but these occurrences form a 

 small percentage of the total when compared with nestings near streams. Rec- 

 ords of one hundred and twenty nests, from literature and specimens, show 

 nests placed in twenty-nine different species of plants. Close to eighty per 

 cent of the plants used were deciduous: willows were represented most frequently 

 and constituted thirty-five per cent of the total. Second in species representa- 

 tion, however, is the evergreen coast live oak (Quercus agrifolia), with twelve 

 per cent of the total. Nevertheless, species of next ranking frequency are all 

 deciduous; these are, in order, alder {Alnus rhombifoHa), big-leaf maple (Acer 

 macrophyllum) , blackberry {Ruhus vitif alius), Cottonwood (Populus), and elder- 

 berry {Sambucus glauca). 



Nests are placed in trees and bushes, usually at a height of six to twelve feet 

 above the ground. Among height records of 163 nests from various localities 

 in California, I found the average to be ten feet above ground. Seventy-eight, 

 or 66 per cent, of these nests were placed between four and twelve feet above 

 ground. The support for the nest usually consists of a crotch or fork in a group 

 of horizontal or vertical secondary branches. * * * 



The nest is a bulky, loosely constructed affair, ordinarily composed of slender 

 twigs, plant stems and rootlets, in the base and outer walls, and of finer stems 

 and rootlets in the lining. * * * 



Building of the nest is done by the female. Suitable nesting material is nor- 

 mally sought within one or two hundred feet of the nest site and occasionally 

 as far as 350 feet. The male usually follows her while she is gathering nesting 

 material and he may accompany her to the general vicinity of the nest; however, 

 I have never seen a male carry nesting material nor in any way aid in the actual 

 construction of the nest. * * * 



Construction of the nest takes from three to four days. Most of the building 

 occurs in the mornings. Visits to the nest become less frequent and more irregu- 

 lar, as the day progresses, and in the afternoon the nest is visited occasionally 

 without any nesting material. 



W. Leon Dawson (1923) says: "The nest of the Black-headed 

 Grosbeak is of singularly light and open construction, evidencing, 

 as we suppose, the habit of the tropics, where ventilation, rather 

 than conservation of heat, is the object sought. Some nests are so thin 

 that the eggs may be counted from below." He mentions a nest 

 that was kept cool by evaporation: "Instead of the usual lace-work 



