Burns — Deposition and Incubation 281 



(Chimney Swifts) with Httle or no protective Hning, appear 

 at every disadvantage in hastening the development of the 

 embryo; and the comparatively longer periods of incubation 

 would seem to foster this hypothesis. 



There are little data available leading to the effects of cli- 

 mate and season on the period of incubation of individuals 

 of the same species. It is quite probable that the most vari- 

 able periods occur in cool rather than warm climates, and 

 more especially in a season of violent changes. Knight (Cf. 

 Birds of Maine) in considering the period of incubation of 

 some oi the Fringillidce {Lanius hidivicianus migrans and 

 Geothlypis trichas trie has) recognized a variation of from two 

 to four days, due to weather conditions, closeness with which 

 the bird brooded and other correlating circumstances. It is 

 well known that up to a certain stage of development of the 

 embryo, the eggs may be subjected to a cooling process by 

 exposure to the weather for some time without endangering 

 the embryo beyond retarding the growth temporarily and 

 lengthening the period somewhat beyond the normal time ; 

 and also, that the sun may relieve the parent bird of part of 

 her task unless the temperature is driven too high and the 

 germ destroyed. 



The number of days of incubation of the species in the list 

 appended has been compiled from - various sources, and in 

 many instances from single records, some of which may be 

 inaccurate and are questioned; others may be subject to re- 

 vision ; but none are included without good authority. 



Podilymhus podiceps. ried-billed Grebe. — 21 ( ?) clays. 

 Gavia inimer. Loon.^29 days. 

 Cepphiis grylle. Black Guillemot. — 21 days. 

 Lariis argentatus. Herring Gull. — 26 or 27 days. 

 Lams franlclini. Franklin's Gull. — 18 or 20 days. 

 Sterna hirimda. Common Tern. — 21 days. 

 Sterna dongalM. Roseate Tern. — 21 days. 

 Sterna fuscata. Sooty Tern.- -26-20 davs. 

 Hydroehelidon niger surlnamenslfi. Black Tern. — 17 days. 

 Anous stolidus. Noddy. — 35-36 days. 

 Oceanodroma leucorJwa. Leach's Petrel. — 30 (?) days. 



