THE DUCK SICKNESS IN UTAH. 15 



THE CAUSE. 



In the course of the investigations it has been established definitely 

 that the duck sickness in Utah is caused by the toxic action of certain 

 soluble salts found in alkali. In other words, it may be said that it is 

 due to poisoning by alkali, as that term is used in the West. By 

 actual experiment it has been found that the duck sickness may be 

 caused by the chlorides of calcium and magnesium. Experiments 

 have indicated that other salts may be incriminated in Utah and 

 elsewhere, but this statement is made with reserve, as it has not yet 

 been definitely established. 



The Salt Lake Valley is well cultivated and productive and owes 

 its fertility almost entirely to irrigation. In the last 15 years the 

 amount of arable land actually under water has greatly increased, and 

 the stream flow at the river mouths has correspondingly decreased. 

 In midsummer of ordinary years little or no water now passes the 

 irrigation dams on Bear Iiiver. The water found at that season in 

 the lower channels comes from such small tributaries as enter below 

 the dams and from seepage from water used in irrigation. Practically 

 the same condition holds in the other streams that flow into Great 

 Salt Lake. Thus irrigation has decreased the amount of water sup- 

 plying the marshes on the lake front, and the resulting slow drainage 

 induces stagnation over large areas. After June 15, as the spring 

 waters in Bear River recede, great expanses of mud flat are laid bare 

 in the sun. Surface evaporation and capillary attraction rapidly 

 draw the salts held in solution in the mud to the surface and there 

 concentrate them. As the mud becomes drier these concentrates are 

 visible as a white deposit or scale (efflorescence) . This in many cases 

 is exposed only an inch or so above the surrounding water level 

 (PI. I, fig. 2). In the large bays strong winds bank up the water and 

 blow it in across these drying flats. As it advances it takes rapidly 

 into solution the soluble salts, largely sodium chloride, but containing 

 calcium and magnesium chloride also. This inflow of water carries 

 with it quantities of seeds and myriads of beetles, bugs, and spiders, 

 washed out of crevices and holes in the dried and cracking soil. The 

 ducks come in eagerly to feed on this easily secured food and work 

 rapidly along at the front of the advancing water, each bird hurrying 

 to get his fill. Many individuals in this way secure a sufficient 

 quantity of these poisons to render them helpless. As the water 

 recedes again small pools are left in shallow depressions, and other 

 ducks and shorebirds feeding in these are affected. 



When this phenomenon was understood the writer was able in 

 many cases to predict that with certain strong winds sick birds 

 would occur in numbers in certain localities, and after a proper 

 interval to send out and have them brought in to the laboratory. 

 The alkaline deposits at the mouth of the large channel known as 

 Brown's Overflow were specially strong in the chlorides of mag- 



