164 . BULLETIN 191, UNITED STATES NATIONAL MUSEUM 



decoys, even if the relation is the result of accident purely, might save 

 some nests from discovery and destruction by persons not closely 

 observant. 



The inaccessibility of the nest because of its position on small limbs 

 far above ground is suflficient to save it from the ordinary prospects for 

 destruction by people climbing to it. Although the nests can be reached, 

 the handicap is too great for most climbers. Forty to sixty feet is the 

 normal height above ground for these nests. Thus the birds can live 

 close to human habitation and nest with greater freedom from the kind 

 of molestation ordinarily encountered by nesting colonies of black- 

 billed magpies. This may account partly for the greater apparent lack 

 of fear generally shown by the yellow-billed birds. 



The mild winter climate in the range of the yellow-billed magpies 

 seems to encourage, or rather to permit, an exceptionally early start at 

 nest-building. In Monterey County, even in the mountains at the 

 highest levels inhabited by the species, magpies regularly begin to build 

 around the middle of December, before the shortest days come. Often 

 a nest will reach a late stage of construction during a series of warm days 

 at this season, but the coming of storms interrupts the progress, and 

 the pairs rejoin the flock. With the return of warm, clear spells in 

 February or March the building is quickly resumed. Normally the nests 

 are completed soon enough for the laying to be completed before the 

 end of March. Thus the egg-laying comes four to six weeks before the 

 corresponding stage in the cycle of the black-billed birds living near the 

 same latitude, but subjected to the more rigorous climate of the 

 interior. 



Warm, cloudless days late in January seem to arouse an extra amount 

 of nesting activity, even when they follow as much as a month of nearly 

 complete inactivity. Once, nest-building at lining stage on January 29 

 was carried on through a light rain. In three hours of morning watch- 

 ing, the pair carried 12 loads of material, sticks or mud, to the nest. 

 Through a cloudy period the following morning the magpies were busy 

 foraging, but when the sun broke through the clouds they went imme- 

 diately to the nest. On the same date of the previous year, soon after 

 a rain stopped and while it was still cloudy, several magpies were 

 perched qtu'etly in the vicinity of nest sites. One working pair left 

 when the rain started again. 



In this locality twigs for nests are regularly pulled from valley oaks, 

 sycamores, and black locusts. Sometimes many in succession are tugged 

 at before one can be loosened. The birds have some trouble in picking 

 a route through the trees where the twigs they carry will not catch on 

 the branches. During active nest-building, periods from 10 to 30 minutes 



