EFFECTS OF DDT AND OTHER INSECTICIDES 



Table 1. — Population records for 9 species of birds that appeared to he most 

 seriously affected by application of DDT dust 



Species 



Texas wren 



Carolina wren 



Kentuclty warbler 



Yellow-breasted chat 



Cardinal 



Blue grosbeak 



Painted bunting 



Lark sparrow 



Field sparrow 



Total 



Number of pairs 

 counted before 



dusting 



Number of pairs counted during the first 6 

 days after dusting 



1st day 2d day 3d day 4th day 5th day 6th day 



17 



Other Species of Wildlife 



Four insectivorous rough green 

 snakes (Opheodrys aestivus) and 

 one large spiny lizard (Sceloporus 

 olivaceous) were found dead in 

 the study area after the dusting 



operations. It is believed that 

 mortality among these forms of 

 wildlife was heavy, although be- 

 cause of their secretive habits and 

 the heavy ground cover compara- 

 tively few victims were found. 



FIELD TESTS 



AGRICULTURAL RESEARCH 



CENTER, 



BELTSVILLE. MD. 



At the Agricultural Research 

 Center, Beltsville, Md., a 90-acre 

 tract covered with a 5-year-old 

 growth of scrub and saplings was 

 sprayed experimentally with DDT 

 in the proportion of 5 pounds to 

 an acre, and a detailed study was 

 made of the effects on the bird 

 population. 



Prior to spraying, repeated cen- 

 suses determined the nesting-bird 

 population on a 30-acre plot at the 

 center of the test area and also in 

 a comparable check plot situated 

 half a mile away. The area was 

 sprayed on the morning of July 3, 

 1947, and the effects on the birds 

 were noticeable within 24 hours. 

 Although the extremely dense 



undergrowth impeded the search 

 for sick or dead birds, seven indi- 

 viduals with typical DDT symp- 

 toms were seen on the day after 

 the spray application. Census 

 counts revealed a rapid decline in 

 populations. The number of Mary- 

 land yellowthroats decreased 63 

 percent in the first 24 hours, and 

 the total decrease for the species 

 during the period of the study 

 was 79 percent. Prairie warblers 

 declined 64 percent in numbers 

 during the first day and at the end 

 of 48 hours they were down to 7 

 percent of their prespray popula- 

 tion. A slight increase in the 

 numbers of this species was noted 

 a week later, however, which may 

 have been due to movement of in- 

 dividuals into the plot from sur- 

 rounding areas. House wrens de- 



