40 U.S. NATIONAL MUSEUM BULLETIN 237 part i 



Eggs. — The eggs of the rose-breasted grosbeak vary from three to 

 five, with four appearing to be the commonest number in a set. They 

 are ovate, sometimes tending to rounded ovate or elongated ovate, 

 and have httle gloss. The ground is "microline green," "pale Nile 

 blue," "pale Niagara green," or "bluish glaucous," and they are well 

 speckled, spotted, or blotched with such shades of brown as "raw 

 umber," "auburn," "chestnut-brown," "cinnamon brown," and 

 "mummy brown." Generally the spots are quite evenly scattered 

 over the entire surface with a tendency to concentrate toward the 

 large end, and on the heavier marked types the spots may be confluent, 

 forming a solid cap over the top of the egg. 



The measurements of 50 eggs average 24.6 by 17.7 millimeters; 

 the eggs showing the four extremes measure 26.7 by 18.6, 25.7 by 19.1, 

 20.3 by 17.6, and 23.4 by 16.8 millimeters. 



Young. — Incubation is shared by both sexes, the handsome and 

 conspicuous male doing his full share, often singing as he sits on 

 the eggs. 



Burns (1915) gives 14 days as the period of incubation for the rose- 

 breasted grosbeak; elsewhere (1921) he states that, according to other 

 observers, the young remain in the nest for 9 to 12 days. H. R. 

 Ivor (1944) records the incubation period as 12 to 13 days in his aviary. 



The young birds are fed by both parents. Roberts (1932) ^vl'ites: 



Occasionally both birds were busy caring for the young at the same time, but 

 generally they took turns at half-hour intervals. They were feeding chiefly 

 red-elderberries from a clump nearby. Once the male and once the female, after 

 an absence of half an hour, returned with a supply of insect food, giving the 

 entire amount to the nestling that happened to be nearest. On these occasions 

 not only was the old bird's bill full of insects on arrival, but there was a con- 

 siderable quantity concealed in the gullet, which was regurgitated in successive 

 small amounts. During one of the male's turns at feeding he came and went 

 twenty-eight times in thirty minutes, always bringing elderberries from a bush 

 only a few feet distant and feeding the same nestling fifteen times in rapid 

 succession. 



Ira N. Gabrielson (1915) made an intensive study of the nest life 

 of a family of these grosbeaks, spending nearly 60 hours in a blind 

 over a period of six days. He and his helpers watched carefully 

 from a distance of 3 to 5 feet and "did not see a single feedmg that 

 was clearly regurgitative." He explains the method of feeding in 

 great detail. His table shows that during the 60 hours the grosbeaks 

 brooded theu- yomig for a total of 15 hours and 49 minutes, in periods 

 ranging from 1 hour and 19 minutes to 6 hours and 54 minutes. His 

 food table shows the amounts of the various items fed to the young, 

 among which larvae formed the largest item, with various seeds a 

 poor second; insects, fed in still smaller quantities, included small 

 butterflies and moths, flies, crickets, beetles, and grasshoppers; 



