\ 
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 aflected, 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 involying 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 steady 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 
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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 urigation 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. 
1 =. 
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. 
ag 
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 
