MORTALITY AMONG WATERFOWL. 7 



It is well known that a large percentage of the afflicted birds recover 

 if they are given fresh water. During the investigations at the mouth 

 of Bear River, 586 sick ducks of 6 species were taken from the flats 

 and placed in pens at the Duckville Gun Club, where there was running 

 water from Bear River. Of this number, 426 birds, or 73 per cent 

 (see p. 9), entirely recovered. Had the cause of the trouble been 

 bacterial infection, such a recovery would not have been possible. 

 The large assortment of species of birds affected, ranging from grebes, 

 ducks, gulls, shorebirds, and snowy herons to an occasional land bird, 

 is in itself an argument against the disease theory and points unmis- 

 takably to the conclusion that a poison is the real cause. Diseases 

 which are fatal to even closely allied species are not common, and 

 one involving many species among birds belonging to several different 

 orders is unknown. 



The fact that a similar mortality occurs in California also goes to 

 prove that the trouble is due to a salt or an alkali. In a careful study 

 of local conditions there, it was possible to establish this similarity 

 and to check doubtful points encountered in the Utah work. 



Around Great Salt Lake the birds undoubtedly sicken in the shallow 

 water bordering the mud flats. As these flats dry after high water, 

 salts and alkalis crystallize on the surface of the ground. When light 

 rains form pools on the flats, or when a stead}^ wind blows the water 

 across the dry barrens, pintails, green-winged teal, and other water- 

 fowl follow, eager to feed on the newly flooded lands. As the highly 

 soluble salts are taken up by the water from the previously dry sur- 

 face, the birds feeding here sicken and die in large numbers. Every 

 unusual outbreak on Bear River during the past summer was found 

 to correspond with some such phenomenon. In other localities, as 

 the mouth of the Weber, the poorly drained pools contain a solution 

 concentrated by evaporation. As soon as irrigation ceases and there 

 is a great increase in the amount of water coming down the river the 

 constant flow steadily drains the flats, removing the stagnant water, 

 and the mortality ceases almost at once. 



At Tulare Lake, Cal., it may be found that the mortality will 

 increase when the water is blown out by the wind to cover new ground. 

 During the summer of 1914 large areas along the south shore of the 

 lake were flooded before wheat planted there was ready to harvest, 

 and on these flats were found great numbers of ducks and other birds 

 dead. 



Birds resident on Bear River undoubtedly establish a certain 

 degree of immunity from the mortality. In spring when migrants 

 first return from the south it is said that a few sick birds may be found 

 along the overflows. Later these disappear and few of the breeding 

 individuals are markedly affected until mid- July. It is certain, 

 however, that water harmless to these individuals is highly toxic to 



