2 Department Circular 261 , U. S. Dept, of Agriculture . 
WHAT A BIRD CENSUS IS. 
By a bird census is meant the exact enumeration of the birds 
actually nesting within th$ boundaries of a selected tract of land. 
Birds that only visit the area should not be counted, no matter how 
close to the line their nests may be situated. Approximate figures, 
though of interest as descriptive of the tract, are quite useless for 
purposes of comparison. Only the person who surveys the land has 
the necessary knowledge of conditions to tell whether “ 2-4 ” means 
2, 3, or 4 pairs of birds. Reports so rendered can not be used in 
tabulating results. 
HOW TO DO THE WORK. 
The most convenient way of taking a bird census is to count the 
singing males early in. the morning before they begin to feed. Then 
every male bird can be found usually in full song, and near the nest 
site; and, after migration is over, it may safely be considered to 
represent a breeding pair. 
Begin at daylight some morning at the height of the breeding sea¬ 
son, and zigzag back and forth across the tract, counting the singing 
birds. Care must be exercised to count each bird only once (espe¬ 
cially if it is necessary to retrace one’s steps) and only one of a 
pair. Mistakes in the latter particular are especially to be guarded 
against in the case of species in which the sexes are nearly or quite 
alike. The count should be repeated at least once, a few days later, • 
or checked by subsequent observations throughout the breeding sea¬ 
son, to be sure that no birds have been missed and that all birds 
counted actually nest within the selected area. In the case of un¬ 
usual species, and especially those outside their usual breeding range, 
the nest, must be found or other satisfactory evidence obtained to 
show that the birds are actually breeding and are not merely wan¬ 
derers or delayed migrants. A note regarding this evidence should 
accompany the report. 
THE TIME TO BEGIN. 
Censuses should be made after the migration is over, at the height 
of the breeding season, when the greatest number of birds have eggs 
or young in the nest. If the work is done too early, some individuals 
may be counted as nesting that will go farther north before they 
breed, and if done so late in the season that the young are on the 
wing, some may have left the area where they were hatched. In 
the latitude of Washington, D. C.—latitude 39°—the first count 
should be made about June 1; in the latitude of Boston, work 
should not begin until at least a week later; south of Washington, 
a correspondingly earlier date should be chosen. 
AREA TO BE COVERED. 
The plot chosen should contain from 40 to 80 acres. A tract of less 
than 40 acres, especially in the case of farm land, will seldom be 
representative, and 80 acres are as much as can be accurately covered 
by one enumerator under most circumstances. So far as possible, 
areas should be selected on which conditions are not likely to change 
