10 THE WILSON BU LLETIN— March, 1921 



of their feet in coiijuiiction witli almost iiiiinediate eyesight 

 and the earh^ development of the nervons s^^stem? 



There can be no donbt that nidicoloiis habits are not 

 only beneficial in many instances to an arboreal or insular 

 existance, but that they are in time inevital)le to that mode 

 of life. However, it is not a special adaptation to a gre- 

 garious habit, since so many birds of nidifugous habits 

 also nest in colonies. 



It seems to me that a more logical conclusion to the 

 nidicolous habits of so many terrestrial nesters would be 

 attributal)le to a primitive habit of breeding on islets or 

 cliffs, or in caves, crevices or burrows; insular or elevated 

 situations of any kind chosen primarily for seclusion and 

 found advantageous for the enforced confinement of the 

 young until they became more robust to withstand the 

 elements and avoid their enemies; in countless succeeding 

 generations the temporary disuse of limbs and slower de- 

 velopment of some of the sense organs would result in one 

 thing, just as we now observe the beginning of the same 

 phenomena in the enforced sedentary life of the young 

 Murros and Auks. The individual or species unable or un- 

 willing to carry food to their young, would have to conduct 

 them to the feeding ground, seek a more accessible situa- 

 tion for their nests where the precocious young could feed 

 and exercise, or perish. Therefore nearly all sea birds 

 nesting exclusively on small islands are nidicolous. The 

 exceptions include the Murrelets, possibly some of the 

 Longipennes, and the Flamingoes ; probably because of 

 the situation of their nests in reference to accessibility to 

 the sea or to a comparatively recent resort to insular breed- 

 ing. On the other hand, we have documentary proof of the 

 typically nidicolous Gannet nesting upon a rocky islet for 

 upward of six or seven hundred years {Cf. Gurncn, The 

 Gannet, p. //// ) and doubtless it has so nested for untobl 

 ages, since it has never been known to nest on the main- 

 land. 



Notwithstanding the diagnosis of the Nidicohie and 

 Nidifugie by Dr. Newton and Dr. (radow, the line of de- 

 nmrcation in some instances is exceedingh' faint and re- 



