tid 
ArticLtE I—The Orchard Birds of an Illinois Summer. By 
STEPHEN A. ForBES AND ALFRED O. Gross. 
From 1894 to 1917 the Illinois State Laboratory of Natural History 
(since merged in the Natural History Survey of the State), of which the 
senior author of this paper was director, was active in quantitative studies 
of the plankton of the rivers and lakes of Illinois, making common use, 
in securing collections, of a ring net of very fine mesh, hauling it definite 
distances and at a fixed rate, measuring the product of each haul, identify- 
ing and sometimes counting the plankton organisms collected, bringing 
into comparison by this means the yield of different waters, situations, 
and seasons, and drawing such inferences as to cause and condition as 
were warranted by the data so obtained. 
Having realized for many years the urgent need of numerical data 
concerning the species of birds in the state as indispensable to their valu- 
ation as ecological, and especially as economic, agencies it occurred to the 
senior author in 1905 that an equivalent of the plankton method might 
be used in the ornithological field by putting in place of the plankton net 
two men who should walk in parallel lines a definite distance apart, should 
identify and count all the birds flushed by them or crossing their track 
on a strip of a given width—say 150 feet—and should make at the same 
time a precise record of the kinds of surface and situations which they 
were traversing, of the distances traveled over each successively, and of 
the kinds of birds seen and the numbers of each kind on each such sec- 
tion of the 150-foot strip. The product of such a series of expert observa- 
tions would be like that of a huge net a hundred and fifty feet wide, 
‘drawn in straight lines across every kind of crop or other surface vege- 
tation,* by which all the birds found there should be caught and held 
until they had been identified and counted. The data so obtained would 
evidently be quite as useful for their purpose as those of the plankton 
net, and the results of their collation and analysis would be quite as 
dependable. 
A satisfactory test of the method having been made during the sum- 
mer of 1905 on a 400-acre grain and stock farm belonging to the Uni- 
versity of Illinois, two assistants were engaged, both students of the Uni- 
versity at the time—one the junior author of this paper, who was respon- 
sible for the identification and counting of the birds, and the other a 
companion whose duty it was to walk at a measured pace at a fixed dis- 
tance to the left of his leader, and to count and record the number of 
* Forests of tall trees were avoided, since the birds there could not be listed ex- 
haustively ; and in orchards, the more open woods, patches of close shrubbery, and the 
like, the strip surveyed was usually narrowed to sixty feet. 
