678 



ON SECONDARY SEXUAL CHARACTERS IN BIRBS. 



sexual characters, search has always been made in the repro- 

 ductive environment. But the correlation between secondary- 

 sexual dimorphism and vulnerability to enemies indicates that a 

 solution to the problem may possibly be found to be related to 

 the activities associated with the escape from enemies, and 

 especially if it could be show^n that the sexes do not bear the 

 same relation to the environment as regards escape from enemies. 

 The author has attempted to show elsewhere (' Controlled 

 Natural Selection,' 1914) the lines along which solution may 

 possibly lie. 



Reference List of Birds. 



Jacamars (Galbiilidse). 

 Kingfishers (Alcedinidie), 

 Motmots (Momotida?)- 

 Mouiid-birds (Megapodiidfe). 

 Mouse-birds (Coliidse). 

 Nig'htjars (Caprimulgidss) . 

 Owls (Strigidfe). 

 Parrots (Psittacidse). 

 Passerine Birds (Passeridie). 

 Penguins (Spheniscidaj). 

 Petrels (Procellariidre). 

 Pigeons (Columbidie). 

 Putf-birds (Biiceonida^). 

 Rails (Rallidffi). 

 Rollers (Coraciidse). 

 Sand-Grouse (Petroclidse). 

 Shore-birds (Charadriidas) . 

 Storks (Ciconiidse). 

 Swifts (CypselidEe). 

 Thick-knees (Gildicnemida;). 

 Tinamous (Tinamidfe). 

 Toucans (Rhamphastida?). 

 Touracous (MusophagidtF). 

 Trogons (Trogonidfe). 

 Woodpeckers (Picidse). 



