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292 TROPICAL NATUREtion of very large, there is a corresponding increase in thenumbers of very small species.The much greater size reachedby many tropicalinsects is no doubt due to the fact that thesupply of food is always in excess of their demands in thelarva state, while there is no check from the ever-recurringcold of winter ;and they are thus able to acquire the dimensionsthat may be on the whole most advantageous to the race,unchecked by the annual or periodical scarcities which in lessfavoured climates would continually threaten their extinction.The colours of tropicalinsects are, probably, on the averagemore brilliant than those of temperate countries, and some ofthe causes which may have led to this have been discussed inanother part of this volume. 1 It is in the tropics that wefind, most largely developed, whole groups of insects whichare unpalatable to almost all insectivorous creatures, and it isamong these that some of the most gorgeous colours prevail.Others obtain protection in a variety of ways; and theamount of cover or concealment always afforded by theluxuriant tropical vegetation is probably a potent agent inpermitting a full development of colour.BIRDSAlthough the number of brilliantly-coloured birds in almostevery part of the tropics is very great, yet they are by nomeans conspicuous, and as a rule they can hardly be said toadd much to the general effect of equatorial scenery. Thetraveller 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 outhow many beautiful living things are concealed byits densefoliage and gloomy thickets. A considerable number of thehandsomest tropical birds belong to family groups which areconfined to one continent with its adjacent islands, and weshall therefore be obliged to deal for the most part with suchlarge divisions as tribes and orders, by means of which todefine the characteristics of tropical bird-life. We find thatthere are three important orders of birds which, though byno means exclusively tropical, are yet so largely developedthere in proportion to their scarcity in extra-tropical regions,1 Chapters v. and vi, post. The Colours of Animals and Plants.