100 ECOLOGY AND LIFE HISTORY OF THE COMMON FROG 



account there are ten ponds, and arrangements had been made with 

 the landowners for work to go on all round the pond at any hour of the 

 day or night. Observations were made in four seasons, 193 1-1934, but 

 mainly in the last two. A fairly busy road passes alongside the pond, 

 and large numbers of frogs were killed by the traffic. It is reasonable 

 to suppose that the same fraction of the total numbers of frogs crossing 

 the road was killed every night. This provided a method of estimating 

 quantitatively the amount of migration, for I passed along the road 

 almost every day early in the morning, and had only to collect the 

 bodies to get the information I needed. 



In the winter of 1933 I came to the conclusion that, if the smell 

 hypothesis was correct, I should fmd frogs working their way up 

 streams that flowed out of ponds, because these streams would contain 

 odorous water. Frogs, hopping at random in the fields, on coming to 

 such a stream have only to follow it upwards to reach the pond. They 

 ought not to be found to the same extent in ditches that do not have 

 their origin in ponds. The winter was wet, and, when I started night 

 observations, the ponds were full. On 9th March, there were many 

 frogs already in Large Totteridge, with much croaking. On the loth, 

 I searched the rising ground above the pond, which includes several 

 ditches running into it, but found no frogs. On the road, however, I 

 found three recently killed ones, all pointing towards the pond. In 

 the drainage ditch that runs under the road, and contains pond water, 

 there was a pair facing the pond about a yard from it. Farther west on 

 the road, there was a dead female facing the pond. In Middle 

 Totteridge, a pond not usually used by frogs, there was a female on the 

 west side, and at the roadside six yards farther west, there was a male 

 facing the pond. No frogs were seen in West Totteridge. 



On the 15th, there was much croaking in Large Totteridge, but I 

 could see no frogs going to it. There was a pair at the roadside edge 

 of Middle Totteridge, and I found a female at the south-west comer, 

 a male in the outflow ditch to the west, and, farther along the same 

 ditch, a pair scrambhng up the bank. On the i6th it was raining. 

 Frogs were in East Totteridge, and I found a female crossing the road 

 to it. I found no frogs in the ditch leading out of this pond to the east. 

 There were several pairs and some single animals in the ditches along- 

 side the footpath opposite Large Totteridge, and there were several on 

 the road, all apparently working their way to this pond, and some more 

 in the ditch flowing from Middle Totteridge. There was no croaking 



