THE HONEY-GUIDES 81 



Somewhat less like wax, but still of interest as comparable materials, 

 are the cambium and bast of trees. In his study of the food habits 

 of the aberrant American woodpecker, the yellow-bellied sapsucker 

 (Sphyrapicus varius), McAtee (1911, p. 17) found that these items 

 formed 16.7 percent of its diet. 



Another item of suggestive value, even though only inferential in 

 nature, is expressed by "L. S. V. V." (Ibis, vol. 92, p. 330, 1950) in a 

 review of a paper by Fisher and Hinde on "The Opening of Milk 

 Bottles by Birds." He expresses the thought that this recently 

 developed habit may have "started by tits pecking at the waxed tops 

 because of the fat-content." While wax does not have the "fat- 

 content" he seems to assume, it does have a "fatty" texture, which 

 may be attractive to the birds. 



Origin of cerophagy 



While it is clear that wax-eating is not wholly peculiar to the honey- 

 guides, it is true that no other birds show such an avidity for beeswax, 

 or consume it for its own sake. How the honey-guides came to feed 

 so extensively on wax is, of course, unlaiown, but there are some 

 pertinent data worth mentioning here. 



Aside from the fact that a peculiar and restricted habit such as 

 cerophagy is hardly likely to have been an ancestral trait, there are 

 two independent bits of suggestive evidence which indicate that 

 probably the group descended from a noncerophagous ancestral 

 stock. One is the fact that honey-guides get no wax in their food 

 until they are practically full grown; the various host species feed the 

 parasitic nestlings on their own diet, which does not include beeswax. 

 Cerophagy therefore seems to be something added to the more 

 ordinary entomophagy common to so manj'^ groups of small birds, 

 and not something essential to the gi'owth and development of the 

 honey-guides. 



The other line of evidence is the complete absence of any anatomical 

 specializations for wax-eating. Beech er (1953), who dissected a num- 

 ber of honey-guides at my request and compared them with other 

 picarian groups, reports that the heavy jaw musculature of honey- 

 guides is as unspecialized as that of the barbets, but in the honey- 

 guides the bill and its musculature are generally weaker, although 

 the palatine retractors are strong, possibly to give a slightly more 

 powerful bite at the tip of the bill. The honey-guides furthermore 

 show no specialization of the digestive organs, no sign of enlarged 

 palatine salivary glands such as occur in all the nectar-eating groups 

 (Dicaeidae, Nectariniidae, Meliphagidae, and Coerebidae). 



309265—55 6 



