552 Mr. D. A. Bamiermaii on the [Ibis, 



Partis c. tenerifcB (Plate XV. fig. 2), Parus c. ombriosus 

 (Plate XV. fig. 4), aiul Pants c. palmensis (Plate XV. fig. 3). 



Can it be tbe brighter refleeted light from the snows of 

 the Peak of Tenerife which has affected the plumage of 

 Fringilla teydea teydea and so caused it to be brighter than 

 the Gran Caiiarian Blue Chaffinch living in the Pinar 

 Pajonal, where the light may be slightly less bright ? 



The daily search for food is more likely to cause structural 

 differentiation than any other factor which avc can name. 

 The Barn Owl of the eastern islands (Tyto alba <jracilirostris) 

 is strucluially modified by having a long slender bill, so as 

 more easily to obtain its food among the holes of the 

 lava rocks, for it lives chiefly on lizards. This is a fairly 

 obvious change which has taken place in the bird to aid it 

 in its struggle for existence, for the western Canarian Barn 

 Owl has many more opportunities of feeding on mice and 

 beetles than the allied form we have been considering, and 

 is therefore unmodified in this respect. Doubtless there are 

 other less obvious instances in the avifauna of the ( Janaries, 

 the birds of which tend to possess stronger tarsi and longer 

 bills than their Continental allies, though this character is 

 not always constant. 



The presence of enemies in an island has already been 

 mentioned, and this leads to the need of Protective Resem- 

 "blance and possible requirement of Mimicry for pui'poses of 

 aggression; the two expressions "protective resemblance" 

 and " mimicry ^^ must not be confused. There are no 

 instances of mimicry among the birds of the Canary Islands, 

 and indeed it is very rare among all birds, being confined 

 almost entirely to tiie Ckickoos, of which there is no resident 

 form in the Archipelago. 



Protective Resemblance, on the other hand, is well illus- 

 trated. Vv^e need only instance the Rock-Sparrow, tiie Courser, 

 tlie Sand-Grouse, the Quail, and the Bustard, although the 

 instances in the Canarian avifauna could be greatly multi- 

 plied, especially among the young of many species. Of the 

 cases cited the Bustaiil is the most instructive, obviously 

 descended from the Houbaia Bustard of North-West Africa; 



