16 BULLETIN 2 08, UNITED STATES NATIONAL MUSEUM 



Knowledge of the breeding of too many of the honey-guides is still 

 insufficient to permit of generalizations of more than temporary use- 

 fulness. It may be mentioned, however, that egg-pecking by the 

 laying hen is much more frequent in Indicator indicator than in 

 /. minor; that in the majority of cases for both these species only one 

 egg is deposited in any one nest; that in the majority of cases the young 

 parasite is the sole survivor of the nest contents. The species of 

 Indicator, as far as known, largely restrict their parasitism to hole- 

 nesting birds (including species that breed in enclosed nests, such as 

 some swallows). While the ornithologist may consider it "only 

 natural" for a picarian bird such as Indicator to lay its eggs in nests 

 of a picarian type, it must be emphasized that the birds involved are 

 by no means all of this sort. Starlings of several species, ant-eating 

 chats, swallows, and yellow-throated sparrows are victimized as well 

 as barbets, woodpeckers, bee-eaters, and hoopoes. Furthermore, 

 Prodotiscus insignis departs even further, laying its eggs in open cup- 

 shaped nests of species of Zosterops and Apalis, a completely dis- 

 similar group of hosts. We know almost nothing of the nestling 

 stage of Prodotiscus, but in Indicator the range of hosts poses a very 

 interesting problem. As Lack (1948, p. 33) has shown, birds with 

 short incubation periods have short nestling periods as well (by 

 nestling period is meant the time from the hatching of the egg to the 

 time when the young bird is ready to leave the nest), but there is one 

 notable exception to this rule — the barbets, woodpeckers, toucans, 

 and their relatives, in which the incubation period is fairly short (a 

 little over two weeks) while the nestling period may be a month or 

 even longer. The honey-guides (at least Indicator) agree with this 

 group, having incubation periods of about 12-16 days, and nestling 

 stages of from 35-40 days. This means that a honey-guide in a 

 barbet's, woodpecker's, or hoopoe's nest fits fairly well into the 

 normal time limits of the host's breeding cycle, but that one in the 

 nest of a sparrow, swallow, chat, or starling gTeatly prolongs the 

 normal duration of nestling care and feeding for the foster parent. 

 And yet these birds can and do rear honey-guides. One may only 

 wonder if the group of activities loosely covered by the term "care 

 of nestlings" is one of those things that grows on itself and is there- 

 fore capable of very considerable extension. It would seem, however, 

 that probably the range of host species was originally more restricted 

 to birds of similar breeding cycle characteristics when the parasitic 

 habit began in the honey-guides than it has since come to be. Even 

 now, the passerine host records are considerably fewer in number 

 than are those of picarian and coraciiform victims. This further 

 suggests that the host predilections of Prodotiscus insignis are rela- 

 tively recent, which is in keeping with the conclusion that Prodotiscus 



