8 THE AUDUBON (BU CCE 
box with mud and rounded the corners with the same material. Later she 
moved several miles south and nested again, building a nest similar in 
every respect to the earlier structure. 
Most nests have full complements of eggs by the first week in April. 
In this first nesting the eggs number four, five or six, averaging slightly 
more than five to a nest, with a better than 90% maturity. Recently 
several letters have been received—one from a museum, one from the New 
York office of the National Audubon Society—asking a verification of the 
interior dimensions of my box plans. Several persons have changed or 
enlarged this size. Certainly this is wise if an operative has big hands. 
It makes the interior large enough to allow easy access. But the box as 
described in my plans is larger than the nest cavity of a downy wood- 
pecker, which is the favorite site of the bluebirds, and it will safely protect 
and develop six babies. But once have I encountered seven eggs laid by 
one mother in a single nest, and I have handled and banded literally thou- 
sands of young bluebirds. I have found the size sufficiently large. 
The second nesting finds three, four, and five egg complements; but 
the season has advanced, the weather is much warmer, and the mother has 
already reared one brood. Only 53% of the young mature safely. 
The eggs normally are a delightful blue, yet albinism is very common. 
About 5 to 6% of the nests contain creamy white eggs, yet Mrs. Laskey, 
of Nashville, reports that babies born from white shells in turn lay blue- 
shelled eggs. In Nashville, Tennessee, where she experiments, bluebirds are 
permanent residents and the same birds often use a box several times in 
succession. In Adams County the birds are migrants, and a banded bird 
using a box on Route 96 seldom repeats. It normally wanders and I often 
find its second nest on Routes 104 or 36, several or many miles away. 
During normal seasons the size and shape of eggs is constant. How- 
ever, in 1943 I found many variations. There were several pewee eggs— 
yolkless little blue eggs about half the normal size—and one jumbo egg was 
as large as a quail egg and contained a double yolk. Pictures of these eggs 
will in all probability be published later in the season in Bird Banding 
Magazine. 
Predation is limited. As I post the box with the barbed fence wire 
protecting one side, I seldom find damage from cats. Normally I place the 
box within several posts of the corner or intersection of two right angle 
fences. The corner normally harbors a few trees and bushes which furnish 
protection and food. Never place the boxes too close to wild grape vines 
or bushes, as inquisitive chipmunks, deer mice, or flying squirrels might 
discover the precious eggs. Snakes occasionally find and strip the boxes 
of young. However, the percentage of loss from such sources is small. 
The worst interloper is the house wren. Normally the bluebird is 
located and has young by the time the male wren appears (April 16 to 21). 
On such years egg piercing is almost negative. The wrens are already 
established by the time the first brood of little blues take to the air, and 
the parents have rested and reestablished themselves before the wrens 
consider nesting a second time. 
