288 
IOWA ACADEMY OF SCIENCE Vol. XXIV, 1917 
above, measures on the inside ll/ 2 inches across by iy 2 inches 
deep and on the outside 2 1 ./> wide by 4 inches deep. It is made 
of plant fibers, grasses and leaves and is lined with plant fibers 
and very fine grasses. In other cases a few occasional hairs 
may be found in the lining. All of these materials are very com- 
pactly woven together into a rather firm structure. 
THE EGGS. 
In such a nest the four or five eggs are laid, and incubation 
Fig. 44. — The three young vireos which hatched from the four eggs in 
the above nest. 
begins immediately. The duration of the incubation period, as 
illustrated in nest number 11, is about thirteen days. 
A SITTING HABIT. 
During incubation several nest habits characteristic of the 
Bell’s Yireo have been found. For instance, in nest number 
10 the bird had a habit of sitting absolutely motionless at the 
edge of the nest — this at more or less regular intervals. While 
in this attitude the bird would not even move its head from 
