1914] Grinnell: Mammals and Birds of tht Colorado Valley 67 



finer analysis (for example, see Spanieling, 1908). A more or less 

 detailed description of the associations observed in our 1910 explora- 

 tions is herewith offered, as a necessary prelude to further discussion. 



In the lists of species, grouped according to apparent associational 

 preferences, all mammals found by our party are included, and all 

 the birds treated in the "General Accounts" except sixteen species, 

 which are of transient occurrence and uncertain forage-ground like 

 swallows, or else so rare as to make even approximate appraisement 

 impossible. 



Qualifying terms are appended in each case: whether of exclusive 

 (excl.) occurrence in the association under discussion, or of maximum 

 (max.) abundance, or of minor (min.) abundance. Obviously a 

 species of exclusive occurrence is entered in but one of the associational 

 lists, while one marked max. in one list is to be found marked min. in 

 one or more of the other lists. It is to be taken for granted that in 

 species of easy locomotion, individuals may occur in transit across 

 other associations than the one or ones in which it is characteristically 

 present t n masst . 



There is necessarily more or less uncertainty in many cases, and 

 where the doubt is strong, owing to lack of knowledge, a question 

 mark is added. With birds, seasonal occurrence is indicated by the 

 terms: resident (present throughout the year), winter (present 

 throughout the winter, in certain cases including fall and spring also), 

 summer (present during the breeding season, in certain cases including 

 spring and fall also), transient (merely passing through during migra- 

 tion). 



River Association 



BIRDS 



Gavia immer: excl.; winter Erismatura jamaicensis: excl.; winter 



Sterna forsteri: excl.; transient Chen liyberboreus hyperboreus: excl.; 

 Phalacrocorax auritus albociliatus: winter 



excl.; winter and transient Plegadis guarauna: excl.; transient 



Pelecanus erytkrorliynchos : excl.; win- Mycteria americana: excl.; summer 



ter and transient Ardea herodias treganzai: excl.; res- 

 Mergus serrator: excl.; winter ident 



Anas platyrhynchos: excl.; winter Butorides virescens antlionyi: excl.; 

 Nettion carolinense: excl.; winter transient 



Querquedula eyanoptera: excl.; trail- Nycticorax nycticorax naevius: excl.; 



sient resident 



Spatula elypeata: excl.; winter Grus canadensis: excl.; winter (?) 

 Dafila acuta: excl.; winter and transient 



Marila affinis: excl.; winter Fulica americana: min.; transient 



