378 Roberts, Colony of Yellow-headed Blackbirds. 



Auk 

 Oct. 



Among a number of birds there is a remarkable variation dis- 

 played in the nest-building ability, some individuals showing such 

 defective instinct in the selection of nesting sites and such a lack 

 of skill in workmanship that they are almost unable to construct 

 serviceable nests. 



The usual full complement of eggs is four, sometimes three or five. 



The usual period of incubation is ten days. 



The eggs of a set rarely all hatch at the same time, usually a 

 period of two to four days being consumed. 



The study of this colony of Yellow-headed Blackbirds met with 

 early interference and later was prematurely terminated by an 

 annoying and unexpected series of events, a brief account of which 

 may be of some interest. Very early in the work it became evident 

 that eggs were disappearing from the nests and between this time 

 and the termination of the inspection June 13 every nest in the 

 colony, except one, was emptied of its contents — eggs and newly 

 hatched young — by some marauder or marauders, the identity of 

 which could not be determined. The one unrifled nest contained, 

 June 13, four nestlings several days old and one infertile egg. 

 Assuming that these were also destroyed, which is almost a cer- 

 tainty, there was not a single young bird reared by this colony of 

 Yellow-heads and all the season's effort went for naught. In all, 

 seventy-seven eggs and fifty-three young birds were taken. Nine- 

 teen of the thirty-six nests in which eggs were laid were emptied of 

 their contents before the full quota of eggs had been deposited. 

 Sometimes the eggs and young disappeared one or two at a time, 

 more commonly the nest was completely emptied between one visit 

 and the next. Usually the nests were not soiled or disarranged in 

 any way. In a few instances there were pieces of egg shells 

 clinging to the reeds or lying in the water below the nests, and once 

 or twice blood stains on the inside or rim of the nest. In one nest 

 there remained two tiny feet and some pieces of flesh, and in 

 another nest four feet, showing that in these instances at least the 

 young birds were dismembered and devoured piecemeal. Once 

 the dead body of a nestling that had fallen from the nest and been 

 drowned in the water below, disappeared during the same night 

 that its fellows in the nest above were disposed of. 



Watch and examine as closely as we could we were unable to 



