24 BULLETIN 208, UNITED STATES NATIONAL MUSEUM 



mention is made to the effect that the tip of the mandible is equally 

 as hard as the maxillary callosity, but it is suggested by inference 

 rather than by actual statement that the two are similar. 



In this connection, I examined alcoholic specimens of nestlings of 

 several species of woodpeckers {Colaptes auratus, Picuides tridactylus, 

 and Dendrocopos pubescens) and one barbet (Megalaima asiatica). 

 The barbet showed no sign of any mandibular callosity, but had the 

 short, somewhat upturned symphesis of the two rami hard, like the 

 maxillary egg-tooth and cap (the rest of the bill being softer) and 

 terminating in a sharp point, in this respect not wholly unreminiscent 

 of the sharp mandibular hook of Indicator indicator and of I. minor. 

 This point, it must be emphasized, was not an extension from the 

 mandible but merely the form of the gonydeal edge of the union of 

 the two mandibular rami; it could be distinguished more readily by 

 touching with the finger than it could be seen even with a hand lens. 

 In two examples of the three-toed woodpecker, Picoides tridactylus, 

 the tip of the maxilla was white and hard with a small egg-tooth on 

 the middorsal ridge just where the tip itself turned down a little; 

 the mandible was noticeably longer and had its ramial symphysis 

 similarly hard and whitish and very slightly upturned. This con- 

 dition was also found in two specimens of the flicker, Colaptes auratus, 

 and in three downy woodpecker chicks, Dendrocopos pubescens. In 

 all three species the upward terminal inflection of the mandible and 

 the downward curvature of the maxilla just at the locus of the egg- 

 tooth can easily be overlooked; they are not sizable, conspicuous 

 features and consequently they have gone almost unnoticed in the 

 literature of these birds. The hooks of Indicator chicks are not too 

 different in kind from these beginnings. Chapin (1924, p. 335) has 

 suggested that these hooks m.ay be "homologous with the extensive 

 calcareous cap which at first covers the entire tip of the upper 

 mandible of young woodpeckers." Our present examination bears 

 this out. 



Thus, while there is some evidence for the occurrence, elsewhere 

 among birds, of double bill callosities, it remains that the condition 

 found in the honey-guides is unique. We need much more informa- 

 tion on the bills of newly hatched honey-guides of other species and 

 genera before we can hope to enlarge our understanding of this 

 phenomenon, but it appears to be a specialization of such a degree 

 as to argue for the great antiquity of the mode of life towards which 

 it is an adaption. For a detailed description of the use of these 

 hooks by the honey-guides, the reader is referred to the account of 

 the nesthng lesser honey-guide (p. 206). 



