98 ECOLOGY AND LIFE HISTORY OF THE COMMON FROG 



moves a rubbish-heap, or takes up a drain, and finds frogs therein. 

 The frog-dealers are reputed to obtain their suppHes from rivers and 

 streams, but they do not write papers about their methods. 



It is obvious that if frogs are to escape destruction by frost, those 

 that hibernate on land must be sheltered, and almost certainly in the 

 dark, a fact of importance for the next chapter. Those in the water are 

 often in the dark, too, for they are buried in mud, or in drains. But 

 sometimes they are in the hght, and can be seen from the bank. One 

 of the Observer's correspondents described the frogs as spreading 

 themselves out over the bottom of the pond when the sun was shining. 

 In one of the ponds in which I have found frogs, they were sheltering 

 under stones in the dark, but in the other they were in the light. 

 Perhaps the most interesting letter was from a Pohsh observer, Miss 

 I. Rovzewska, who found frogs separately frozen into the ice of a 

 small pond. They revived when thawed in warm water. In Poland, 

 ponds normally freeze to the bottom, but it is evident that, never- 

 theless, the habit of underwater hibernation is found in that chmate as 

 well as in the mild British Isles. 



Hibernating frogs are not torpid as a rule. One I found under water 

 with its head wedged in a crevice of the bank was in the same place 

 a week later. I have also accidentally killed a frog in January in my 

 garden which was sheltering under a board with frost on its upper 

 surface. The frog had recently eaten a meal, and I suspect that it had 

 been foraging on the previous night, which had not been very cold 

 for the time of the year. The frogs I dredged up from the streams 

 swam rapidly away when I released them. 



Frogs are, of course, well adapted for underwater hibernation, for 

 they have good cutaneous circulation and at low temperatures have 

 no need of lungs. 



The duration of hibernation must vary very much in different parts 

 of the range. In the high Alps, snow only goes from its habitats in 

 early June and may descend again in September, so that the frogs 

 hibernate for nine months. In the south-west of England and Ireland, 

 frogs may spawn in December. If these frogs go into hibernation at 

 about the same time as other frogs, say in late October or November, 

 then it appears that they cannot hibernate for more than about one or 

 two months. In these areas, hibernation may well start later than in 

 the rest of the country, so that the period may be even shorter. 



It is generally considered that hibernation is necessary for normal 



