VI AY 5 1923 
UNITED STATES 
DEPARTMENT of AGRICULTURE 
DEPARTMENT CIRCULAR 261 
------- — - 
Washington, D. C. April, 1923 
♦ 
THE PURPOSE OF BIRD CENSUSES AND 
HOW TO TAKE THEM. 
By MAY THACHER COOKE, 
Assistant in Biological Investigations, Bureau of Biological Survey. 
WHY TAKE A BIRD CENSUS? 
One of the chief means of solving many problems concerning the 
distribution of bird life is found in bird censuses, or counts of breed¬ 
ing birds, such as have been made for several years under the direc¬ 
tion of the Biological Survey. It is very desirable that this form of 
research work be continued on an increased scale, in order that more 
information may be available regarding the numerical distribution 
of the birds breeding in different sections of the country and on 
different types of land; the relative numbers of the several species; 
and the fluctuations that take place in bird life. Knowledge of the 
approximate numbers and relative abundance of birds, both game 
and insectivorous, such as can be gained in this manner, is not only 
of great value but is also a prerequisite for the proper administra¬ 
tion of Federal and other laws for bird conservation. For this 
reason data are needed to show what effect existing laws have had; 
how much birds have increased under protection; and what species 
have been most affected. 
To obtain satisfactory results the work must be continued for 
many years. It is of the utmost importance that the counts be 
repeated on the same tracts year after year, in order that the accumu¬ 
lated records may furnish material for comparisons by which to 
learn what changes take place in the number and distribution of 
birds. For this many more series of reports are needed. Usually 
records for at least five years for a given tract are necessary for 
forming an adequate idea of the bird life thereon. 
The department has no funds to pay for this work, but must de¬ 
pend wholly on the assistance of volunteer observers. The work of 
those who have helped in the past is greatly appreciated; and it is 
hoped that not only will their cooperation be continued, but also 
that many more will give assistance in this interesting and valu¬ 
able work. 
29649°—23 
