18 BULLETIN 208, UNITED STATES NATIONAL MUSEUM 



incubating the eggs and of feeding and caring for the young.^ In 

 other words, the stock closest to the honey-guides are birds in which 

 both sexes are active in all phases of the normal sequence of reproduc- 

 tive activities, and this, in turn, suggests that the originating factor 

 or factors that led to parasitism in the Indicatoridae were proba- 

 bly such as affected both sexes more or less equally. 



The fact that some of the barbets have the habit of using old nest 

 holes of other species as well as their own for sleeping places during 

 the nonbreeding season, and that they often are quite gregarious in 

 these "dormitories," vaguely suggests the possibility that the mutual 

 exclusiveness of nesting sites normal to most birds (and to barbets 

 also) may be subjected to some infringement or weakening thereby.^ 

 However, this is only a passing thought; it may help to account for 

 the tendency of Indicator minor to enter nest holes of barbets and 

 other birds even when not in breeding condition itself. So far, noth- 

 ing is known of the sleeping habits of honey-guides, whether they 

 use old excavations in trees as dormitories or whether they pass the 

 night amid the dense foliage of the trees. Any information on any 

 usage by honey-guides of old nesting sites of other bii'ds may well 

 provide suggestive data. 



Although nothing is known as to the factors that may have con- 

 ditioned, if not brought about, the advent of brood parasitism in the 

 honey-guides, we have some slight evidence as to the geological time 

 of their operation. In our discussion of the evolution of the species 

 of honey-guides it was pointed out that the family is of at least Miocene 

 age, and that its geographic spread appears to have taken place in the 

 Pliocene. The fact that the parasitic habit is present in all sections 

 of the family suggests that it is of greater antiquity than the differen- 

 tiation of the group into its component species and genera, and this, 

 in turn, suggests that the original honey-guide stock probably was 

 parasitic prior to the Pliocene spread of the family. In his recent 

 study of the evolution of parental care in birds, Kendeigh (1952, 

 p. 297, footnote) writes that the evolution of the different behavior 

 patterns of the various families and orders of birds probably developed 

 chiefly during the sixty million years of the Cenozoic period. The 

 fact that a reproductive mode such as brood parasitism could hardly 

 have become successful until the patterns of parental care in the 

 various hosts were well fixed further indicates that these patterns 



2 This is also true of the related puflfbirds (Bucconidae) , in three species of which 

 both sexes are known to share these duties. (Skutch, 1948.) 



* Thus, in the Central American prong-billed barbet, Semnornis frantzii, 

 Skutch (1944) found as many as 16 birds in one such dormitory, although as the 

 breeding season approached the paired barbets began to sleep in their own nests 

 and these dormitories became deserted. 



