200 Conservation Department 



portion to their width than wider streams less favorably situated. 

 Thus it is shown that width alone is not a true criterion for avail- 

 able drift food in streams. Stream environment must also be 

 considered. 



By comparing the average weights, shown in Table 4, of drift 

 food per 100 square feet found in each type of stream habitat, 

 i. e., arboreal, densely brush-shaded, semi-exposed and exposed, it 

 is seen that the arboreal type of environment contributed the most 

 food per 100 square feet of surface, .013 grams. The four types 

 of stream environment intergrade more or less but are sufficiently 

 distinct for general comparisons. 



The arboreal type of stream environment as considered here 

 consists of a tall growth of hard woods and conifers bordering the 

 stream and generally not shading the stream center. Such habitats 

 naturally shelter large numbers of terrestrial insects and since it 

 is somewhat open to the wind, many are doubtless dislodged and 

 fall into the water. Probably because of these factors, this type 

 of habitat furnished the largest amount of drift food per 100 square 

 feet of surface. Stream habitats densely shaded with low brush and 

 small trees are common at the headwaters of streams in this 

 vicinity. These also shelter many insects but being less open to 

 the force of the wind, fewer insects are dislodged into streams 

 at such places and less drift food is present in them. Semi- 

 exposed stream habitats are bordered partially by pasture and 

 partially by scattered trees such as alders, willows and sycamores. 

 In exposed habitats the streams flow entirely through meadows and 

 pastures and have only low grasses and herbs on their margins. 

 The semi-exposed habitats furnished slightly more food, per 100 

 square feet of surface, than the exposed, probably because the 

 few trees growing along the banks of the former, harbored 

 more terrestrial insects than the low grasses and herbs along the 

 banks of exposed streams, and because the force of the wind on the 

 scattered clumps of tall vegetation found in the semi-exposed areas, 

 would dislodge many possible forage organisms. 



Three drift catches were made at dusk at stations 1, 2, and 6 

 in July to determine whether or not more food was available in 

 streams at this time of day. It was found that slightly less drift 

 food was available at this time as compared to that found during 

 the full daylight hours. Two drift studies were also made at mid- 

 night. Although the differences in productivity per unit area were 

 very slight between dusk and midnight drift catches, it was found 

 that in daylight hours, slightly larger amounts of forage organisms 

 were available, less being found at dusk and least in the midnight 

 catches. However, the figures available are too few to draw 

 definite conclusions on the diurnal fluctuations in stream drift 

 at this time. 



A general comparison of weights of the drift catches showed 

 that the greatest amounts of drift food was available in June, 

 there following a decrease through July and the least in August. 



