FOOD, HIBERNATION AND MIGRATION 99 



reproduction. If this is so in nature, then this might be another 

 iactor Hniiting the distribution of this animal to countries cold enough 

 for liibernation to occur. But our warm areas owe their mild climates 

 so much to oceanic influences that places much further south on the 

 Continent have colder winter climates than Cornwall or Kerry, and, 

 on the whole, it seems more likely that other factors are at work, as 

 suggested in Chapter i. 



As so often happens, this question is made more difficult because the 

 physiological experiments are carried out on frogs in captivity, 

 commonly under very artificial conditions. However good the 

 observations and experiments may be, they could be quite irrelevant 

 to events in the field. A frog in Cornwall which never hibernated for 

 long, if at all, might in nature become sexually mature all the same — 

 who knows? 



In spite of the generally satisfactory state of the information about 

 hibernation, it is, of course, incomplete and qualitative. Dolk and 

 Postma (1927) showed that frogs use fat but not carbohydrate during 

 liibernation, but apart from this there do not seem to be any ecological 

 quantitative measurements, such as temperatures of the hibernacula, 

 losses or gains of water, speed of digestion and frequency of feeding. 



Migration 



In the late winter and early spring, frogs move from their winter 

 quarters to the breeding ponds. We have now to consider how they 

 behave when on migration, what prompts them to begin the journey, 

 and how they are guided to their destination. 



There is a fairly considerable literature on the migration of other 

 species, but, except for some observations by Neal (1956) dealing with 

 the arrival in the pond, there seems, to be no detailed work on the 

 actual migration of this frog, except in my 1935 paper. It seems there- 

 fore desirable to begin with an account of what happens in the field, 

 before going on to analyse the reasons for the things that have been 

 seen. 



It is sufficient for this purpose to take that part of the migration that 

 took place near the main pond. Large Totteridge, used for these 

 observations. Reference should be made to the map. Fig. 25. The 

 pond was situated nearly at the highest point of a ridge rising from a 

 valley at about 200 feet to the summit at about 410 feet, only about 

 thirty yards from the pond. Witliin the area chosen for this shortened 



