£o\) Wetmore, Birds of Lake Burford, N. Mex. [ April 



mens. On June 15 I had a pair of Mallards under observation 

 for some time and from their actions was certain that they were 

 mated as the female remained constantly near the male and the 

 two had all of the mannerisms of mated birds. A short time after 

 I came nearer and finally shot them both. On dissecting the fe- 

 male I found that the ovary showed little or no development 

 while the ova exhibited the diseased condition known as black 

 atrophy, an affection that is little understood, but one that is 

 known to render birds sterile. The oviduct in this Mallard could 

 be barely distinguished and showed no development whatever, 

 though in healthy breeding females taken at this same time the 

 oviduct was greatly enlarged, and exhibited the condition of tur- 

 gidity common to the breeding and laying season. The male that 

 accompanied this female was molting rapidly into eclipse and had 

 already lost much of the breeding plumage. On examining the 

 sexual organs in this bird I found the cloacal portion still swollen 

 and enlarged, but the testicular substance degenerating so that 

 it had been resorbed to a point where the testes were shrunken to 

 one-fourth of the full normal size. 



The instances outlined here are a further example of the care 

 necessary in allotting ducks as breeding in certain localities simply 

 because of their presence there in breeding season. This would 

 apply especially to more unusual records in extension of range. 

 Further observations on the occurrence of mated sterile females 

 among ducks and other birds are of importance and the question 

 is one that will repay careful investigation. 



Migration 



At the time of my arrival there was still some movement in 

 migration both among the smaller insect-feeding passeriform 

 species and the larger water birds. Cliff swallows were not ob- 

 served until May 25, Western Warbling Vireos arrived about May 

 31, and Orange-crowned Warblers, June 2. Grinnell's Water- 

 thrush was seen on May 23 and 25, and the Pileolated Warbler on 

 May 26 and June 2. 



A few observations seem to indicate that Lake Burford is on 

 one of the lines of flight for birds passing to and from the Salt Lake 

 Valley, Utah. Snowy Herons observed at the lake at intervals 



