1914] Grinnell: Mammals and Birds of I III ('nlorado Vallnj 11 



the conditions above the Latruna Dam. Here the whole association 

 had been effaced by drowning. On the other hand, the me.squite is 

 unable to exist on the desert proper, even in the larger washes. Only 

 at the mouths of these did scattering examples extend away from the 

 actual river bottom, and then, in the most favored places, for not more 

 than a quarter of a mile. 



Man's occupancy of the region has affected the mesquite associa- 

 tion more than any other. The great value of the mesquite trunks 

 for fuel has led to its practical disappearance as a tree along much 

 of the lower course of the river. The steamboats which once plied 

 regularly between Needles and Yuma are said to be chiefly respon- 

 sible for this depletion. Several pumping plants contributed to the 

 demand for fuel. Mesquite trees are very slow of growth; tracts of 

 stumps now mark many areas where luxuriant groves once stood. 



A considerable number of low-growing plants find places as elements 

 in the mesquite association, but by far the most important to the 

 animal life is the mesquite itself. This shrub, or tree, provides both 

 shelter and food, the latter through its fruit and foliage (see pi. 6. 

 fig. 7) either directly or by way of insects. The mesquite serves also 

 as the host of a parasitic plant (pi. 6, fig. 6). a species of mistleto(! 

 {Phoradeiidron calif ornicum) , which when in blos.som is \isited by 

 myriads of insects, and w-hich produces an abundant and almost con- 

 tinuous crop of berries. Several of the winter and resident birds of 

 the mesquite a.ssociation depend almost wholly on these mistletoe berries 

 for their food. Notable among these are: Pliainoprpla, Mimus. Orro- 

 scoptes, Planesticus and Sialia. 



Four species of breeding birds {Pipilo aberfi, To.rostoma crissalr. 

 Vermivora luciae, and Phainopepla nit ens) find in the mesquite asso- 

 ciation the center of their abundance. One mammal is characteristic 

 of the same association, namely Xeofom/i alhicjida v< nusta. 



Saltbttsh Association' 



BIRDS 



Lophortyx gambeli: min.; resident PhalaenoptiUis nuttalli nitidus: iiiin. 



Zenaidura macroura marginella: resident (?) 



max.; winter (hordeiles acutipennis texensis: min. 



Geococcyx calif ornianus: min.; resi- summer (only as a forager) 



dent Sturnella neglecta: exel. ; winter 



Phalaenoptilus nuttalli nuttalli: Poceeetes gramineus confinis: exc-l.; 



min.; winter winter 



