276 The Wilson Bulletin -^ No. 90 



My conclusions are based upon the statements of authors, 

 the manuscript notes of Messrs. T. A. Elliot, Jr., North East 

 Harbor, Me. ; John F. Ferry, Chicago, 111. ; Henry Link, Wa- 

 terloo, Ind. ; Angus McKennon, DeFuniak Springs, Fla. ; 

 Leonard S. Pierson, Wayne, Pa. ; Alfred C. Redfield, Cam- 

 bridge, Mass. ; A. C. Read, Isle of Pines, Cuba ; Charles H. 

 Rogers, Princeton, N. J. ; Ernest W. Vickers, Ellsworth, 

 Ohio; Aliss Farida Wiley. Sidney, Ohio, and my own obser- 

 vations. 



The duties of incubation are usually performed by the fe- 

 male, often with the assistance of the male, or the male may 

 not participate in the actual brooding process but may carry 

 food to the female and later assist in caring for the young. 



Exact knowledge of the amomit of assistance given the fe- 

 male by her mate during the incubating season does net ap- 

 pear to be of much importance in consideration of the com- 

 parative periods. When one sex forages and incubates unaid- 

 ed, however, the period is usually prolonged beyond that of 

 the normal of the species accustomed to the advantage of an 

 assisting mate ; or possibly in -rare instances like that of the 

 Trochilidcc, Hummingbirds, of species of an entirely differ- 

 ent group of similar size. Clark (C/. Auk, xx, 162) gives an 

 instance of a male Bob-white incubating a late clutch of eggs 

 for 28 days before hatching, apparently several days over the 

 regular period ; while the female was leading her first brood 

 about the vicinity. 



Apparently most colonial species are doubly monogamous ; 

 birds breeding in colonies can seldom conceal their eggs from 

 enemies, therefore have the greatest need of constant protec- 

 tion by either sex. 



Most hole-nesting species are doubly monogamous, though 

 there are some notable exceptions ; one would naturally seek 

 the reason for this in the greater need of animal heat in lieu 

 of the diirect rays of the sun to further the rate of incuba- 

 tion ; rather than that of protection from enemies, of which 

 there is less need than in the instance of the colonial birds. 



In many species and gi'oups where one sex is much more 



