YELLOW-BILLED MAGPIE l65 



elapse when no bird appears at the nest and when the pair is off forag- 

 ing. In the active periods the whole effort of both the birds is directed 

 to getting sticks to the nest and working them into place. 



The urge for nest-building seems to grow stronger with the advance 

 of the season. Also the member-pairs of a colony seem to approach 

 such a synchronized program that they reach the stage of incubation at 

 about the same time even though they do not start building together. 

 However, some examples indicate that nests are sometimes begun long 

 after the normal time. At the Hastings Reservation one season a pair 

 of magpies was watched one morning, on May 11, busily carrying sticks 

 to a nest in its early stages. Several sticks picked up from the ground 

 were carried to it. A magpie was seen to enter this nest on July 24, 

 but no actual use of it was made until the following year. Then a brood 

 was brought off in the normal season. 



Another late start at building a nest was noted in June. On the 19th 

 a magpie carried a stick to a site in a fork about 50 feet up in a sycamore, 

 and where 35 or more sticks already had been placed, many of them 

 within the preceding 24 hours. No bird was seen about this nest again 

 until the early morning of June 24, when each member of the pair 

 brought a stick. Each bird then called and perched near the nest for about 

 a minute and then they, separately, flew off to the ground. Again, a 

 considerable quantity of material had been added since the preceding day. 

 No more material was added. Two birds perched close to the site on 

 June 27, but 5 days later all the magpies on the Reservation left for a 

 period of days, thus apparently ending the story. But early in the 

 morning of July 15 a noisy flock of magpies settled in this vicinity. One 

 of the birds went three times to the partly built, late nest and crouching 

 on it with wings aquiver uttered low, throaty, harsh calls, which sounded 

 like currow, and turned around several times. Half an hour later the 

 same performance was seen at the nest, but there was no further indica- 

 tion of its use at any later time. 



Like the other kinds of magpie, the California one builds a nest that 

 is sought by other birds as a home, but this use seems rather restricted 

 to the sparrow hawk. Nearly every colony of yellow-billed magpies has 

 at least one pair of nesting sparrow hawks. Although it may not be 

 evident all through the season, there is considerable strife between these 

 species when nest sites are being selected. After a given nest has been 

 successfully defended and all the pairs are settled, the two species appear 

 to take little notice of each other. 



Pursuits of magpies by sparrow hawks are noted often in fall, be- 

 ginning in September. Sometimes a magpie turns in a cjiase and pursues 

 the hawk. These pursuits, however, may have little significance in the 



6674&7— 4»— 12 



