96 U.S. NATIONAL MUSEUM BULLETIN 265 



Eviction of nest-mates by nestling cuckoos 



Like the related genera Cuculus and Cacomantis, CJirysococcyx also 

 evinces the behavior pattern of eviction of nest-mates by the newly 

 hatched young. As in the other two genera, this habit is dispalyed 

 only in the first days of the nesthng's life and disappears by the time 

 the young cuckoo's eyes begin to open. Eviction of nest-mates, either 

 young or eggs, has been observed and recorded for five species of 

 CJirysococcyx — lucidus, basalis, osculans, Haas, and caprius, and in- 

 ferred, without actual direct observation, for maculatus, xanthorhyn- 

 chus, and cwpreus. In all probability the habit occurs in the other 

 glossy cuckoos as well, but as yet no data are available on them.^' 



In the case of C. lucidus, Oliver (1955, p. 535) concluded that the 

 parasitism of this species must have a considerable effect on the popu- 

 lation of its chief host in New Zealand, the gray warbler, Gerygone 

 igata, whose "first brood . . . unless delayed, escapes the attention of 

 the cuckoo but [whose] later broods suffer heavy casualties in their 

 nestling stage as the young cuckoo invariably throws out all eggs and 

 young from the nest it occupies . . . ." In other species of Chrysococcyx 

 it appears that eviction of nest-mates is frequent, but not invariable. 

 Both Pitman and Chapin (in Friedmann 1949a, pp. 180-181) have 

 sent me notes on nests containing young of the host and of the cuckoo 

 (caprius), but we do not know if these were instances where the 

 young parasite made no effort to oust its companions or if it tried to 

 do so but failed. 



In a previous discussion (1956, pp. 404-405) I pointed out that no 

 one had yet made a direct observation of the actual evicting act by a 

 young caprius, a statement that is still true a decade later. The 

 precise age, in days, at which the newly hatched young cuckoo be- 

 comes an evictor and the age at which it ceases to be one has been 

 reported with some variation. Thus, Skead (1952, pp. 7, 9) noted that 

 a nestling caprius in a Motacilla nest made no effort to oust the two 

 eggs of the host for its first two days, after which it proceeded to evict 

 them both. In a Ploceus capensis nest, a young didric evicted an egg 

 and a newly hatched young of the fosterer on its second day. In 

 another Ploceus nest the young parasite was half way through its 



" For pertinent published references on eviction of nest-mates see: lucidus — 

 Campbell 1901, p. .581; Dickison 1928, p. 151; Oliver 1955, p. 535; basalis— 

 Campbell, 1901, p. 579; de Warren 1926, p. 78; Dickison 1928, p. 151; Leach 1929, 

 pp. 177-182; osculans — Chisholm 1935, p. 70; maculatus and xanthorhynchus — 

 Baker 1942, p. 155; /riaas— Friedmann 1956, pp. 399-400; MacLeod and Hallack 

 1956, pp. 2-5; caprius — Friedmann 1956, pp. 404-405; Hunter 1961, pp. 5.5-63; 

 Reed 1953, pp. 138-140; Skead 1952, pp. 7, 9; Skead, in Rowan and Broekhuysen 

 1962, p. 28. In addition to these I have numbers of unpublished notes from Pitman, 

 Chapin, and other observers in my files. 



