Burns — Deposition and Incubation 279 



Our largest Passerine, Corvus corax principalis Northzrn 

 Raven, may occasionally deposit its eggs at intervals of every 

 other day. 



Coccyzus americanus Yellow-billed Cuckoo, and C. eryth- 

 rophthalmus Black-billed Cuckoo, are subject to variation ac- 

 cording to locality ; individuals inhabiting the Atlantic slope 

 occasionally seem to require an interval of from two to eight 

 days, but as both species have been known to drop their eggs 

 in other birds' nests and the average number in a set falls 

 away below that of the same species in the West, probably 

 the most satisfactory explanation of the apparent departure 

 from the normal daily deposition, may be found in the para- 

 sitic tendencies of the eastern individual. Not impertinent to 

 the subject, it may be stated that the parasitic nature of the 

 European Cuckoo has been erroneously attributed to its ir- 

 regular deposition and consequent inability to assemble a 

 clutch of eggs ; however this may be, our parasitic Cowbird 

 has been known to drop four or five eggs in as many days, 

 though like the Bobolink, it may now and then depart from 

 the normal. 



Members of a group normally or commonly producing two 

 eggs, deposit at less frequent periods, the Columbidcu, Capri- 

 tnulgidcE and Trochilidce lay on alternate days. The larger 

 Gamidce two or three days apart, and a week or ten days may 

 elapse before the Cathartidce deposit the second egg. The 

 Raptore^ require from one to three or four days interval gen- 

 erally, depending upon size, the g-'cnera Aqiiila, Haliceetus and 

 Bubo, which include some of the largest species and frequent- 

 ly deposit two eggs only, the interval is the maximum. 



Birds laying daily, ordinarily but not invariably, begin in- 

 cubation after the set is completed. The occasional irregular- 

 ities in incubation :are often traceable to exceptional condi- 

 tions ; cold or stormy weather at the time of deposition may 

 induce the parent to cover the nest for a time sufficient to 

 affect the first laid eggs. 



Birds ordinarily exhibiting irregular deposition usually be- 

 gin incubation with the first (sometimes the second or third) 



