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their young mostly on insects, there are very many more 

 species, at least fifteen to one, probably more, of insectivorous 

 birds found in the forest than there are in the open. 



"Frederick J. Jackson." 



Mr. C. F. M. Swynnerton replied, December 22, 1911, 

 describing the conditions in Chirinda forest, Gazaland, S.E. 

 Rhodesia : — 



" You ask whether birds are specially partial here to forest 

 and lizards to open country. 



" Our lizards are specially partial, apparently, to the sparse 

 wooding of our open country, not but that there may be purely 

 Hi] 



arboreal species in Chirinda (apart from Rhampholion marshalli) 

 that have not yet come within my ken. 



" Birds, however, are abundant in both types of country. 

 Bird species are more plentiful in the open country, bird- 

 population to the acre greater, probably, in the forest ; but 

 in this connection it must be remembered that the forest- 

 birds have several ' upper storeys ' to work, the forest trees 

 running from 100 to 180, and exceptionally, 200 feet in height, 

 against the 30 feet or so of the open woodlands, — and the 

 view to take of this sort of thing must be a ' cubic ' not a 

 'square' one ! Again, owing to the greater density of the 

 cover in the forest, the insect population is probably, taking 

 the year round, relatively greater. 



" I should imagine that there may be very little to choose 

 between the forest and the veld in the matter of severity of 

 selection. And that the veld-factors are capable of producing 

 as good mimicry as the forest ones seems to be well shown in 

 the Danaida combination. 



" May not the phenomenon you refer to be, in part, depend- 

 ent on the larval food-plant 1 



"Thus Danaida s food-plant here consists of various species 

 of Asclepias, a genus that I have not found inside the forest. 

 On the other hand the food-plant of A. albimacidata occurs 

 only in forests or in dense thickets. I do not know those of 

 our other Danainae, but, seeing that these belong to the same 

 genus as A. albimacidata, it seems just possible that they may 



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