CIRCULAR 15, FISH AND WILDLIFE SERVICE 



394.0 pairs per 100 acres, a de- 

 cline of 9.5 percent. In the check 

 area, populations during- this same 

 interval declined 10.6 percent, 

 from 376.5 to 336.5 pairs per 100 

 acres. The slight drop in numbers 

 in both areas was believed due to 

 completion of nesting. Territorial 

 maps accounted for practically all 

 the original individuals through- 

 out the study, and numerous nests 

 and family groups appeared un- 

 affected. 



A possible effect of the spray 

 on bird behavior was noted in 

 Townsend's warbler. This spe- 

 cies, normally a canopy feeder, 

 was commonly seen feeding at or 

 near the ground level after the 

 spray application. This unusual 

 habit was not noted prior to treat- 

 ment of the area. A careful check 

 of nests and young of the species 

 showed no measurable effect on 

 either the young or the adults. 



Fishes 



Of the more than 50 streams in 

 the treated area, 40 were known 

 to contain trout and 18 were listed 

 as fair to excellent fishing streams. 

 Rainbow, eastern brook, and cut- 

 throat trout were not affected by 

 the insecticide during the 5-week 

 period of observation. Large pop- 

 ulations of speckled dace and red- 

 sided bream were also unaffected 

 by the poison but cottoids, moun- 

 tain suckers, and black catfish 

 suffered heavy losses in rather 

 limited areas. 



Seventy-two trout stomachs 

 were examined, of which 35 were 

 from trout taken from stream sec- 



tions treated with DDT. Volu- 

 metric comparison indicated a 50- 

 percent reduction in available 

 food, largely in aerial insects and 

 riffle forms. Ants and worms 

 were important items of diet both 

 before and after treatment. Cray- 

 fish, paralyzed by DDT, com- 

 prised 99.2 percent of the contents 

 of the stomachs of 21 brook trout 

 taken in one treated locality, 

 whereas no crayfish were found 

 in stomachs of fish taken in un- 

 treated areas. All specimens were 

 caught by rod-and-line fishing, and 

 there was no evidence that the 

 vitality of the fish declined after 

 treatment. 



The ecology of stream sections 

 that received a heavy deposit of 

 spray was considerably altered. 

 Annelids and molluscs were not 

 affected, but insect larvae and 

 nymphs were virtually eliminated 

 from the riffle fauna. Even in 

 fast-moving streams, lethal quan- 

 tities of DDT were not transmit- 

 ted far beyond the areas of direct 

 application. Such limits were 

 definitely less than 3 miles, prob- 

 ably not more than 1 mile, con- 

 sidering the possible drift of air- 

 borne spray. 



Stream sections in which a se- 

 vere kill of invertebrate life had 

 occurred were soon marked by a 

 luxuriant growth of algae, which 

 completely blanketed many of the 

 riffles. The earliest replacement 

 of riffle organisms was a hatch of 

 mayflies noted 2 months after the 

 area had been treated. 



Although there was no evidence 

 of immediate damage to game-fish 



