168 U.S. NATIONAL AIUSEUM BULLETIN 23 7 pari i 



St. Joseph, Mo,, discovered a nest when it was 75 percent constructed. 

 Two days later the nest contained two blue dickcissel eggs and one 

 brown-speckled cowbird egg, and in 2 more days on June 23, 1952, 

 four dickcissel eggs and one cowbird egg. At noon on July 5, 1952, 

 one dickcissel young was found in the nest which had not been pres- 

 ent 24 hours earher. The incubation period of this bird was 12 

 to 13 days. The other three dickcissel eggs and the cowbird egg 

 did not hatch. The young bird left its nest between July 12 and 

 July 14 at the age of 7 to 9 days. 



Eggs. — The eggs of the dickcissel are immaculate pale blue. The 

 measurements of 50 eggs average 20.8 by 15.7 millimeters; the eggs 

 showing the four extremes measure 23.4 by 17.0, 21.8 by 17.5, 18.3 

 by 15.2, and 20.1 by 14-5 millimeters. The average weight of 20 

 eggs is 2.76 grams. 



The number of eggs in a set varies from three to five, but four 

 is the usual number. Of 29 nests containing complete sets of eggs, 

 5 had three eggs, 18 had four, and 6 had five eggs each; 3 of the 5 

 nests containing only three eggs were under daily observation and 

 no more eggs were added, but one or more eggs may have been 

 destroyed before observations were begun. 



The large number of sterile eggs found was surprising; of 11 nests 

 studied during the summer of 1918, 5 contained one sterile egg and a 

 6th nest had two. It was thought possible that the embryos had 

 been killed perhaps by chilling, but examination of the unhatched 

 eggs proved that development had never started, or at least had not 

 proceeded to an appreciable degree. Incubation is entirely by the 

 female. Sauer (1953) determined the incubation period to be 12 to 

 13 days. When the fully developed embryo is ready to emerge, the 

 egg shell and membranes break around the entire circumference 

 midway between the blunt and pointed ends. The break seems to be 

 made by the exertions of the struggling embryo to straighten its neck 

 and to extend its legs in the effort to free itself. After the egg cracks, 

 it is only a few minutes before the young frees itself entirely. A 

 freshly-hatched chick appears almost naked, for the meager patches 

 of natal down while wet and matted are practically invisible. 



Nesting. — The study of the home life of a pair of birds that nested 

 in the tall weeds and grass along a country roadside supplied many 

 interesting incidents which help portray the character and behavior 

 of the dickcissel. I made the following notes during the nesting 

 season from blinds at close range. One nest, built about 10 inches 

 above the ground, was composed of materials loosely interwoven 

 among the stems of the tall grass and weeds. The tops of the grass 

 and weeds arched over this little home, protecting the eggs and young 

 from the direct rays of the sun and concealing them from the view 



