324 BULLETIN 195, UNITED STATES NATIONAL MUSEUM 



"Twelve nests were made of the following materials, the frequency 

 of use of which is indicated by the numbers in parentheses. Founda- 

 tion: coarse weed stalks (11), leaves (7), paper (7), coarse twigs 

 (5), red-cedar bark (4), grass (3), chestnut bark (1), and lumps of 

 dirt (1). Lining: in each case (12) made exclusively of rootlets." 



Both birds share in the work of carrying sticks to the nest, but the 

 female does the major part of the construction and the shaping of 

 the structure. If the male finds the female at the nest when he brings 

 nesting material, he hands it over to the female for her to manipulate 

 into the nest. On the other hand, if the male is at the nest when the 

 female arrives, he immediately gives her right-of-way. The male 

 accompanies the female on many of her journeys for nesting ma- 

 terial, but a considerable portion of his time is taken up by singing and 

 defending his territory. 



About 5 or 6 days are required to complete the nest, and in one 

 case under observation the first egg was laid during the morning of 

 the day after the nest was finished. One egg was added each morning 

 thereafter until a set of four was complete. During the first few 

 days the female did not incubate continuously but was away from 

 the nest at irregular intervals of time. Thereafter she seldom left 

 her eggs and was fed on the nest by the male. 



On coming to the nest and settling down on the eggs she shifted 

 her body from side to side, working the feathers of the breast and 

 belly around the eggs and permitting them to come in direct contact 

 with naked aptera to receive the heat from her body needed for in- 

 cubation. The nest is usually so deeply cupped that her long tail 

 is thrust upward at an angle nearly perpendicular to the axis of her 

 body, and likewise the head is generally thrown back. 



Eggs. — The number of eggs per set varies from two to five. R. C. 

 Harlow (1918), who examined 110 nests of the catbird in Pennsyl- 

 vania and New Jersey, determined the average to be 4 with a varia- 

 tion of from 3 to 5. Exceptional sets of 6 eggs have been reported by 

 various observers. M. B. Trautman (1940) found a nest at Buckeye 

 Lake, Ohio, on June 24, 1927, that contained 6 eggs. Nests with only 

 1 or 2 well-incubated eggs have been reported. 



The eggs are a deep glossy greenish blue or bluish green, much 

 deeper in tone than those of the robin or wood thrush. They are al- 

 most always without markings, but there are a few rare exceptions. 

 John Nichols has seen the eggs spotted with red. Sage, Bishop, and 

 Bliss (1913) and E. D. Wintle (1883) also reported catbirds as laying 

 spotted eggs. 



The measurements of 50 eggs in the United States National Museum 

 average 23.3 by 17.5 millimeters ; the eggs showing the four extremes 

 measure 26.4 by 17.8, 24.1 by 18.8, 21.3 by 17.8, and 21.8 by 15.8 

 millimeters. 



