THE ANIMAL COMMUNITY 65 



between niches in widely separated communities. In the 

 arctic regions we find the arctic fox which, among other 

 things, subsists upon the eggs of guillemots, while in winter 

 it relies partly on the remains of seals killed by polar bears. 

 Turning to tropical Africa, we find that the spotted hyaena 

 destroys large numbers of ostrich eggs, and also lives largely 

 upon the remains of zebras killed by lions.12^ The arctic fox 

 and the hyasna thus occupy the same two niches — the former 

 seasonally, and the latter all the time. Another instance is 

 the similarity between the sand-martins, which one may see 

 in early summer in a place like the Thames valley, hawking 

 for insects over the river, and the bee-eaters in the upper part 

 of the White Nile, which have precisely similar habits. Both 

 have the same rather distinct food habits, and both, in addition, 

 make their nests in the sides of sand cliffs forming the edge 

 of the river valleys in which they live. (Abel Chapman ®^° 

 says of the bee- eaters that *' the whole cliff- face appeared 

 aflame with the masses of these encarmined creatures.") 

 These examples illustrate the tendency which exists for 

 animals in widely separated parts of the world to drift into 

 similar occupations, and it is seen also that it is convenient 

 sometimes to include other factors than food alone when 

 describing the niche of any animal. Of course, a great many 

 animals do not have simple food habits and do not confine 

 themselves religiously to one kind of food. But in even these 

 animals there is usually some regular rhythm in their food 

 habits, or some regularity in their diverse foods. As can be 

 said of every other problem connected with animal com- 

 munities, very little deliberate work has been done on the 

 subject, although much information can be found in a scattered 

 form, and only awaits careful coordination in order to yield a 

 rich crop of ideas. The various books and journals of orni- 

 thology and entomology are like a row of beehives containing 

 an immense amount of valuable honey, which has been stored 

 up in separate cells by the bees that made it. The advantage, 

 and at the same time the difficulty, of ecological work is that 

 it attempts to provide conceptions which can link up into some 

 complete scheme the colossal store of facts about natural 



