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CIRCULAR 15, FISH AND WILDLIFE SERVICE 



creased 59 percent in numbers 

 during the first 24-hour period 

 and continued to decrease during 

 the six succeeding days. Red- 

 eyed towhees showed a drop of 35 

 percent in numbers, which may 

 have been a reflection of their 

 habit of feeding in duff and litter. 

 Of the five commonest species in 

 the area, three — the Maryland 

 yellowthroat, prairie warbler, and 

 house wren — were reduced 80 

 percent. The total decrease in 

 numbers of the five most abun- 

 dant species, which comprised 77 

 percent of the original popula- 

 tion, was 65 percent. 



The populations of the small 

 mammals in the area were too low 

 for detailed studies of effects to be 

 made. One dead meadow vole 

 was found, however, and DDT 

 was recovered from the tissues. 



PATUXENT RESEARCH REFUGE. 

 LAUREL, MD. 



Late in May 1947 a 117-acre 

 tract of bottom-land woods on 

 the Patuxent Research Refuge, 

 Laurel, Md., was sprayed with 

 DDT by airplane for the third suc- 

 cessive year. For that applica- 

 tion the DDT was used at the rate 

 of 2 pounds to an acre. A casual 

 check of bird residents revealed 

 no effects on the group. No at- 

 tempt was made to get detailed 

 evaluations of the spraying, since 

 the primary objective of this par- 

 ticular investigation is to deter- 

 mine any cumulative effects from 

 repeated yearly treatments. Ex- 

 haustive studies of both the insect 

 and the vertebrate life will be 



made after the fourth or fifth 

 annual treatment of the area, and 

 the findings compared with the 

 detailed information obtained 

 prior to the first spraying. 



BACK CREEK. W. VA. 



A one-mile section of Back 

 Creek, W. Va., was sprayed in 

 1946 with DDT in suspension at 

 the rate of 1 pound to an acre. 

 The results of this experimental 

 treatment were given in the sum- 

 mary of DDT investigations for 

 that year. During 1947, addition- 

 al studies of the bottom fauna were 

 made to determine the extent of 

 recovery. Although bottom or- 

 ganisms were reduced 70 percent 

 in numbers at some stations after 

 the spraying in 1946, investiga- 

 tions a year later showed that re- 

 covery was practically complete. 



On July 23, 1947, a 1-mile sec- 

 tion of Back Creek was again 

 sprayed with DDT in the same 

 proportion as in 1946, but mixed 

 with oil instead of held in suspen- 

 sion. The average quantity of 

 DDT deposited at water level was 

 0.27 pound to an acre, whereas in 

 the tests the year before a some- 

 what greater quantity of 0.39 

 pound to an acre was deposited. 

 Some differences in effect were 

 noted between the two types of 

 formulations. The DDT in sus- 

 pension used in 1946 did not ma- 

 terially reduce the numbers of the 

 surface Coleoptera and Hemip- 

 tera. These same groups, how- 

 ever, were immediately and 

 markedly affected by the lasting 



