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IOWA ACADEMY OP SCIENCE Vol. XXIV, 1917 
creasing or decreasing in numbers. However, at a meeting of the 
Sioux City Bird Club on October 1, 1914, one of the best known 
bird authorities for northwestern Iowa, Dr. Guy C. Rich, made 
the statement that “the Bell’s Yireo has decreased in numbers 
in the last thirty years.” A study of the above series of nests 
seems to support Doctor Rich in his statement. 
PEW SUCCESSFUL BROODS. 
The extreme difficulty in raising young vireos is much em- 
phasized in the above series. With the exception of nest number 
5, which was empty, there were only three successful broods of 
vireos raised out of the thirteen nests. These were numbers 3, 
6, and 11. All others were either abandoned or had Cowbird’s 
eggs. Considering the well known characteristics of the latter 
in hatching early and in preventing the young vireos from get- 
ting sufficient food it is safe to presume that very few vireos 
were raised in the nests containing Co whir ds ’ eggs. This pro- 
portion of only three successful broods out of thirteen, if it is 
representative, and it appears to be nearly so, does not present 
a very bright future, at least for an increase in numbers, for 
the Bell’s Yireo. 
THE MORTALITY IN POUR NESTS. 
During the summer of 1915 close watch was kept of four dif- 
ferent Bell’s Yireo nests to find out the rate and causes of 
some of this mortality. The last four of the above nests were 
the ones observed. 
In nest number 10 the Cowbird’s egg hatched, while the two 
vireo’s eggs were infertile, but on July 3 the young Cowbird 
was found dead and the nest abandoned. Out of four vireo’s 
eggs in number 11 three hatched and the young were raised. 
Both nests 12 and 13 were abandoned, the former after the eggs 
had been chipped and the latter before any eggs had been laid. 
The result of this study was to determine that only one out 
of the four pairs of birds was actually successful in raising 
young vireos. Only three birds came from the four nests. Nat- 
urally the parents nested somewhere else after an unsuccessful 
attempt but, if these observations are representative, they prob- 
ably met with a similar degree of failure to raise progeny in 
their further attempts. Storms, animals, Cowbirds and vermin 
