191^] GrinneU: Mammals and Birds of the Colorado Valley 151 



distinctly whitish. This results in a casual similarity to E. trailli : all 

 of the other characters are normal for difficilis. however. 



There is al.so in the Mu.seum a skin (no. 4302) taken b.y J. G. 

 Cooper at Fort :Mohave, ]\Iay 20, 1861. 



Empidonax trailli trailli f Audul)i)n) 

 Traill Flycatcher 



First detected April 28 and 29. when several were discovered in 

 a tract of willows on the California side within a mile below Potholes. 

 There were several of the birds, keeping in the upper foliage of the 

 trees on ground overflowed from the adjacent canal to a depth of two 

 feet or less. 



On the same side of the river five miles northeast of Yuma several 

 Traill flycatchers were observed May 4 and 5 close along a rapidly 

 filling slough lined with willows. On both sides of the river in the 

 vicinity of Pilot Knob the species was frequently observed up to the 

 date of our departure, May 15. The birds were never detected away 

 from dense willow growths close to the water, just such a type of 

 locality as is chosen elsewhere for nesting ground. This fact and the 

 behavior of the birds led me to believe that they would nest in the 

 vicinity. If so, this is the only Empidonax to breed in the lower Colo- 

 rado Valley. Two specimeiLs taken, nos. 121)10. 12911. both males, are 

 quite like more northern and western breeding birds. 



Empidonax hammondi 'Xantus) 

 Hammond Flycatcher 



First observed April 3, on the California side opposite Cibola: 

 next April 6, at the same place; thereafter almost daily all along down 

 the river, usually in the mid-branches of large willows. Thirteen 

 specimens taken (nos. 12883-12895) from: Arizona side: ten miles 

 below Cibola : California side : oppo.site Cibola, twenty mil&s above 

 Picaeho. eight miles below Picaeho. Potholes, Pilot Knob. At the 

 latter point the species was noted up to and including Jlay 11. It 

 appears that the species is only a transient through the region. 



