26 ECOLOGY AND LIFE HISTORY OF THE COMMON FROG 



The vegetation was abundant, and besides the patches of starwort, there 

 were floating patches o£ algae in many places. The water was clear. 



When the pond was next visited on 20th April, no tadpoles could be 

 seen anyAvhere, and numerous sweeps of the net failed to collect even 

 one. On 26th April, however, tadpoles had returned to the spawn site 

 in large numbers, and were forming a dense and very active aggre- 

 gation. Not many were seen anywhere else. On 3rd May, the general 

 behaviour was similar, but the dense aggregation had moved about 

 2 m further east. Many sweeps with the net were made at the west 

 end, without result. On nth May, no tadpoles could be seen at the 

 places where they had been so abundant and only a few could be 

 collected in the net. The west end now for the first time contained a 

 dense aggregation, both among the starwort and also among some 

 decayed rushes on the north bank, at the collecting spot known as 

 "Sallow." One sweep brought up many hundreds of tadpoles. From 

 Fig. 5 it can be seen that the weights of the tadpoles collected from 

 different places differed considerably. On 21st May, large numbers of 

 tadpoles had returned to "Spawn Site" (about 12 per 100 cm^), and 

 some were seen elsewhere in the pond. There were now definite signs 

 that the tadpoles were dispersing — there were colonies, widely separated 

 from each other, with the intervening spaces free from the animals. 

 Within each colony, the population was dense — in one case, there were 

 as many as 100 per 100 cm^, and the pond was conspicuously crowded 

 with tadpoles. At the next visit, on ist June, it was at once obvious that 

 a change had occurred. Although many tadpoles were to be seen 

 almost all over the pond, there were no dense, heaving masses of them, 

 but, on the contrary, each tadpole was leading a solitary hfe, with few, 

 if any, signs of vigorous feeding movements. On 7th June, some of the 

 animals had metamorphosed, little frogs being seen in the neighbouring 

 ditch as well as in the pond itself. There were, however, still some tad- 

 poles left in the pond, and, on 1 6th June, the patches of algae which 

 had disappeared began to reappear. Reference to Fig. 5 shows that the 

 mean weight of the tadpoles did not increase from 21st May to 29th 

 June, but that after this date there was a sharp increase. The final 

 tadpoles collected were much larger than those that had meta- 

 morphosed weeks before, although there were very few of them. On 

 1st August, no tadpoles could be found. 



The weather during the season was hot and dry almost all the time, 

 with one wet spell in May. The level of the water fell, except during 



