habitats was unknown. The problem of foraging pref- 
erences of purple martins and other swallows could 
better be studied at individual colonies so that habitat 
use can be determined in relation to habitat availabil- 
ity. At present there are no such data available, and 
studies are needed. 
Most significant and interesting are the studies of 
Karl Bartel (1945, 1946, 1955, 1959), who, with the 
help of Alfred H. Reuss, Jr. in the early years, cen- 
sused the nesting martin population of Blue Island, 
Illinois, annually beginning in 1936. Blue Island, a 
city of about 22,000 people in northeastern Illinois, 
has an area of about 3.5 square miles (U.S. Bureau of 
the Census 1960). Between 1936 and 1959, Bartel 
(1959) recorded a low population of 151 pairs (about 
13 birds per 100 acres) in 1937, and a high of 331 
30 
Fig. 27.Adult male and fem: 
martins at nest box. The bird on t 
of the box is a first-year male. 
pairs (about 29 birds per 100 acres) in 1945 i 
1950. On the average, the population varied ¢ 
about 11 percent from one year to the next, but | 
maximum variation was 29 percent between 1937 
1938. Bartel also provided data on nest box util 
tion. Between 1936 and 1948, each year about 60 
cent of the 53 available houses (yearly average) — 
martins. Over a period of years about 92 percen 
the available houses were used by martins, based 
data from Bartel (1946). Of 10 houses that were 
23 years, three had martins every year. At St. Le 
Widmann (1922) had 86 percent occupancy of | 
boxes by martins in 1888. Comparative data 
needed for other areas of the state. . | 
The ups and downs of the Blue Island martin / 
ulation could not be explained on the basis of 
