TIME AND ANIMAL COMMUNITIES 89 



ecological work, that the routine observations taken by meteoro- 

 logists were not always of much use in the study of animals. 

 Their observations are taken at rather arbitrary times and 

 under extremely unnatural conditions, and are therefore often 

 of little value to the ecologist. To take a simple example, 

 meteorological screens are usually fixed at a height of 4 feet 

 from the ground and the instruments in them record the 

 climate at a height where comparatively few animals live. 

 Furthermore, very few animals live in the open at that height — 

 except cows and zebras and children and storks and certain 

 hovering insects. What we have said is particularly true 

 when the communities of animals at night and in the day are 

 being worked out. As a matter of fact, the only kind of data 

 which are of any use in the solving of this kind of ecological 

 problem are accurate charts of temperature, humidity, and rain- 

 fall, obtained from continuously recording instruments placed 

 actually in the habitat which is being studied. In most places 

 only the first of these is available, and even that may be absent. 

 8. A careful study of the changes in external conditions 

 during the day and night with reference to corresponding 

 changes in the activities of animals is very badly wanted, for 

 our ignorance of the matter is profound. It is remarkable to 

 reflect that no one really knows why rabbits come out to feed 

 only at certain times, and on different times on different days. 

 Weather and diurnal changes are no doubt partly responsible, 

 but there our knowledge ends. And yet rabbits are common 

 animals and of great practical importance, and millions of 

 people have watched their habits. We do not know whether 

 Hght, temperature, humidity, or something else determines 

 the appearance and retirement of animals at certain times. 

 About the food-relationships of nocturnal animals we know 

 less than about those of animals which come out in the day, 

 and that is to say we know pathetically little. And, after all, 

 it is quite as important to have information about the factors 

 which limit animals in time as those which limit them in their 

 spatial distribution, from whatever point of view we regard 

 the question, whether from that of evolution or of wider 

 problems in ecology. 



