292 TROPICAL NATURE 



tion of very large, there is a corresponding increase in the 

 numbers of very small species. The much greater size reached 

 by many tropical insects is no doubt due to the fact that the 

 supply of food is always in excess of their demands in the 

 larva state, while there is no check from the ever-recurring 

 cold of winter ; and they are thus able to acquire the dimen- 

 sions that may be on the whole most advantageous to the race, 

 unchecked by the annual or periodical scarcities which in less 

 favoured climates would continually threaten their extinction. 

 The colours of tropical insects are, probably, on the average 

 more brilliant than those of temperate countries, and some of 

 the causes which may have led to this have been discussed in 

 another part of this volume. 1 It is in the tropics that we 

 find, most largely developed, whole groups of insects which 

 are unpalatable to almost all insectivorous creatures, and it is 

 among these that some of the most gorgeous colours prevail. 

 Others obtain protection in a variety of ways; and the 

 amount of cover or concealment always afforded by the 

 luxuriant tropical vegetation is probably a potent agent in 

 permitting a full development of colour. 



BIRDS 



Although the number of brilliantly-coloured birds in almost 

 every part of the tropics is very great, yet they are by no 

 means conspicuous, and as a rule they can hardly be said to 

 add much to the general effect of equatorial scenery. The 

 traveller is almost always disappointed at first with the birds, 

 as he is with the flowers and the beetles ; and it is only when, 

 gun in hand, he spends days in the forest, that he finds out 

 how many beautiful living things are concealed by its dense 

 foliage and gloomy thickets. A considerable number of the 

 handsomest tropical birds belong to family groups which are 

 confined to one continent with its adjacent islands, and we 

 shall therefore be obliged to deal for the most part with such 

 large divisions as tribes and orders, by means of which to 

 define the characteristics of tropical bird-life. We find that 

 there are three important orders of birds which, though by 

 no means exclusively tropical, are yet so largely developed 

 there in proportion to their scarcity in extra-tropical regions, 

 1 Chapters v. and vi, post. The Colours of Animals and Plants. 



