THE AMPHIBIA OF OKLAHOMA 



be noted, however, that not all possible factors were tested. Oxygen determi- 

 nations were omitted deliberately since the prevailing water temperatures 

 (25-33° in all pools) during most of the time indicated that not much could 

 be held by the water. That oxygen was deficient was also indicated by the 

 fact the tadpoles often gulped air at the surface. 



The behavior of tadpoles in forming huge feeding aggregations in lim- 

 ited areas suggested that they might react to concentrations of organic matter 

 locally on the pool's bottom. Some very simple observations were made, both 

 in the pools and in the laboratory, to check this possibility. 



At Pool D at a time when huge feeding aggregations were forming and 

 breaking up into agitated schools, I scratched away the upper layer of organic 

 matter on the bottom in an area approximately one inch square or less. This 

 was done in a region of non-aggregation. Almost immediately two tadpoles 

 found this and began feeding here voraciously. Others joined them in increas- 

 ing numbers till within ten minutes thousands of agitated, struggling tad- 

 poles had piled up in an aggregation, all attempting to feed from this small 

 disturbed area of the bottom. The scratching had been done with my finger 

 and there was a possibility the tadpoles were reacting to me rather than to 

 the bottom materials. I slowly lowered my finger into the water, being careful 

 not to touch the bottom. It was immediately attacked by tadpoles and an 

 agitated aggregation formed about it nibbling so effectively that they could 

 easily be felt. (At other times tadpoles of S. hurierii have attacked my bare 

 feet as I waded a pool.) But when the bottom was disturbed with a small 

 stick, an aggregation formed as before. These observations were repeated 

 several times with comparable results. It was concluded that, under condi- 

 tions in this pool at this time, the tadpoles reacted positively both to a dis- 

 turbance of the bottom and to my finger suspended in the pool. In contrast, 

 tadpoles of several other species, abundant in this same pool, did not so react. 



Comparable observations made in the laboratory support these obser- 

 vations in the field. About five hundred tadpoles of S. hurterii collected from 

 Pool D, six days from egg laying were placed in a large, flat class culture dish 

 filled with clear tapwater. Here they swam almost continuously for several 

 hours each apparently paying no attention to the others. This behavior con- 

 formed to the typical pattern observed many times earlier when no food was 

 available. 



A very small amount of Hartz-Mountain Fish Food (representing a 

 mixed organic food source) was lightly sprinkled on the water surface near 

 the center of the dish. The animals became more active immediately and be- 

 gan to concentrate in the region of the particles, spread by surface tension 

 over the water's surface. Originally, two happened to be near the surface. In 

 thirty seconds, six were there and more were coming up. In one minute fifty- 

 six were concentrated at the surface. In five minutes so many were concen- 

 trated that they could not be counted. In twenty minutes I estimated that one- 

 half of the total were at the surface. 



Another sprinkle of the fish food caused the animals to become greatly 

 agitated, swimming along the surface sometimes in small schools and clumps, 



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