^°'i9l4^^] Recent Literature. 411 



Dr. Defant's report on the influence of weather conditions on migration 

 deserves careful study. It is interesting to note that in tabulating the 

 data to show which days are characterized by the greatest number of 

 arrivals he adopts the same plan used bj' the Delaware Valley Ornithologi- 

 cal Club in ' Cassinia,' except that he does not reject the obviously ' late 

 dates.'— W. S. 



Grinnell on the Mammals and Birds of the Lower Colorado Val- 

 ley.^ — The latest of Dr. Grinnell's studies of California birds and mammals 

 and their distribution has to do with that portion of the Colorado River 

 vallej^ which forms the southeastern boundary- of the state. The expedi- 

 tion which furnished most of the data and material for the present report 

 was made possible by the generosity of Miss Annie M. Alexander, founder 

 of the California Museum of Vertebrate Zoologj'. Dr. Grinnell took per- 

 sonal charge of the field work and was assisted bj' Messrs. Frank Stephens, 

 Joseph Dixon and L. HoUister Jones. The party descended the river 

 /by boat from Needles nearly to the Mexican line below Yuma, making 

 twenty-nine stops, and occupying three months' time, from February' 15 to 

 May 15, 1910. A collection of 1272 mammals and 1374 birds was secured 

 as well as many other specimens. 



To the carefully prepared annotated hst are added chapters on the ' Zonal 

 and Faunal Position of the Region ' ; the ' Associational Areas ' ; ' The 

 Colorado River as a Highwaj^ of Dispersal '; and as a ' Hindrance to Dis- 

 persal ' and ' The Problem of Barriers with Regard to Birds and Mammals.' 



Under these headings Dr. Grinnell continues the discussion of the 

 problems and principles of distribution which has characterized his recent 

 papers. Attention is called to the " two schools of faimistic students," one 

 of which regards temperature as the chief factor in controlling distribution 

 while the other advocates " a composite control, of many factors resulting 

 in ecologic ' associations,' " and the author attempts to* bring these views 

 into accord on the theorj-, which we heartily endorse, that they are 

 due simply to " difference in perspective." He recognizes again zones 

 due to climatic differences; faunas, due to differences in humidity; and 

 associations, due to environmental conditions — both inanimate and 

 animate. 



Eleven different associations are recognized — the River, Willow-Cot- 

 tonwood, Tule, Arrowweed, Quail-brush, Mesquite, Saltbush, Creosote, 

 Catclaw (or Wash), Saguaro, and Enceha (Rocky Hills) — with Usts of 

 characteristic birds and mammals. The species are separated into several 

 categories according as whether they are exclusively restricted to the given 

 ' association ' or are at their maximum or minor abundance there. The 



> An account of the Mammals and Birds of the Lower Colorado "Valley, with 

 Especial Reference to the Distributional Problems Presented. By Joseph Grin- 

 nell. Univ. of Cal. Publ. in Zoology, Vol. 12, No. 4, pp. 51-294, pis. 3-13. 9 text 

 figs. March 20, 1914. 



