568 Mr. R. C. L. Perkins — Introduction to 



competition for food loetween the various species which have 

 similar habits, and between the individuals of each, cannot 

 be doubted. The number of birds that can exist in a given 

 area is obviously only that which can be supported when the 

 food-supply is at a minimum. At the present day, when the 

 " Ohia" is in bloom over miles of country, the food-supply 

 seems inexhaustible ^ but between the flowering periods it is 

 limited, and often leads to a decided migration of the birds 

 either from one district to another, or to dififerent elevations 

 in the same district, where, owing to the varying climate, the 

 trees blossom at different seasons. Certainly the arrival of the 

 " Ohia '' must have been a powerful agent in the increase of 

 individuals of honey-sucking species; and the competition 

 for food must have been much more keen previously. One 

 can hardly doubt that the primitive Drepanid was a honey- 

 sucker, and that the now purely insectivorous, as well as 

 the thick-billed frugivorous forms, were a later development, 

 although the honey-suckers were no doubt at all times 

 partly insectivorous, as they are at present. With the in- 

 crease of the insect-fauna there would certainly be a tendency 

 among the honey-sucking forms to become more largely, 

 or even entirely, insectivorous, as in fact has been the case. 

 The examination of a series of species of the Lobeliacese will 

 show great differences in the length of their flowers ; and while 

 in some the nectar can be reached by the moderate tongue 

 of Chlorodrepanis, in others it can only be procured by the 

 extremely long-billed and long-tongued forms of Drepanids, 

 and the long-tongued Meliphagine Moho, the latter also a 

 peculiar and probably very ancient denizen of the islands. 



A series of observations made on one of the most superb of 

 the Lobeliacese showed that it could only be fertilized by these 

 highly specialized birds. In this species the pollen is mature 

 before the stigma is exserted, by which time the pollen has 

 vanished. The latter cannot be wind-borne, because it is shed 

 in a viscid mass on contact, and so is constantly deposited 

 on the bird's forehead, from which it is difficult to remove it. 

 With these considerations in view the cause of the develop- 

 ment of the most remarkable forms in each group of birds 



