88 U.S. NATIONAL MUSEUM BULLETIN 2 6 5. 



own advantage by reducing the clutch size in the parasitized nest, 

 thereby ostensibly aiding the potential success of the young cuckoo, 

 it is inconceivable, that the laying adult can have any anticipatory 

 purpose. Actually, in many egg-removing parasites the evicting habit 

 of their newly hatched young takes care of possible nest-mate com- 

 petitors, rendering the earlier removal of one or more eggs less impor- 

 tant than it might appear to be. It would seem (but at this state of 

 our knowledge "seem" is the strongest word that may be used) that 

 the function of egg removal by the adult parasite is to keep the total 

 clutch in the nest from exceeding the limits acceptable to the incubat- 

 ing host. 



The glossy cuckoos shed no new light on the early stages of this 

 particular behavioral trait, an evolutionary problem of great interest, 

 but one that remains blanketed in obscurity. In fact, we still do not 

 know if all the species even have the egg-removing habit, although 

 it is highly probable that all do. The habit has been reported on good 

 evidence for only four of the species: lucidus (unpublished data from 

 two observers), basalis (Atkins 1922, p. 314; Ingle 1912, p. 254; Ross 

 1919, p. 303); Haas (Pitman, in litt.), and caprius (Pringle 1946, p. 

 368; Skead, in litt.). To this may be added that it has been said to 

 occiu" in maculatus and in xanthorhynchus, although without direct 

 evidence. In the case of cuprevs it has been suggested by Chapin 

 (1939, p. 203) that the male may remove an egg from a nest occa- 

 sionally, but it is not clear that this is necessarily connected with 

 the deposition of a substitute egg by his mate. 



In connection with C. lucidus plagosus it may be noted that Braddy 

 (1949, p. 238) and Chalk (1950, pp. 219-220) both recorded seeing an 

 adult glossy cuckoo that flew to a thornbill's nest (Acanthiza chrysor- 

 rhoa) and "clung by its feet to the lower part of the nest and rapidly 

 searched for and found the entrance, into which it thrust itself, leaving 

 only the end of the tail exposed. In a split second it withdrew itself 

 backward from the nest with the egg of the thornbill in its bill. This 

 it cast to the ground. A second time it plunged into the nest and 

 repeated the act, except that the second egg thrown out proved, en 

 our investigating it, to be that of its own species . . . ." This obser- 

 vation is given here because it shows the instinctive nature of the act, 

 with no recognition of the difference between the eggs of the host 

 and of the parasite, which is what is tacitly assumed to hold as well 

 for the host in its usual acceptance of the alien egg. In this particular 

 instance both eggs were in an advanced state of incubation, which 

 indicates that a considerable number of days had elapsed since the 

 act of parasitism. It is, of course, impossible to tell if the egg-removing 

 cuckoo had also laid the egg in the nest. Even if it was the same bird. 



