BELL’S VIREO STUDIES 
293 
are all possible causes of this unusual lack of multiplication 
of the species. 
These two things, then, an unusual number of Cowbirds’ 
eggs in nests and the raising of only three vireos in the four 
nests — 10, 11, 12, and 13 — point to a probable diminution in the 
numbers of Bell’s Vireos, at least in 1 he neighborhood of Sioux 
City, Iowa. 
Department of Zoology, 
Grinnell College. 
