NESTING HABITS OF OROPENDOLA CHAPMAN 375 



group 2. She draws herself up to full height, slightly expands her 

 ruffs, with bill down then curls head downward until bill touches 

 lower breast. Zarhynchus meanwhile cuncerned and whines slightly. 

 The performance is repeated." Less marked was the action of two 

 females who, on February 18, 1928, posed on a limb in the sand- 

 box tree with their bills pointed upward, like boat-tail grackles. 



The probability that Cassidix is aware of the conditions existing 

 in a Zarhynclius colony is indicated by the fact that after the nest- 

 ing colony of lUiiS was abandoned Cajisid'ix was not seen in it. On 

 February 2G my journal reads: ''Apparently not an oropendola left 

 in the tree.'' On the following date this entry appears : '" Cassidix 

 in group 2 examines and enters nearly every nest, its longest stay 

 being three seconds. It was opposed only by male and female 

 Lcgatus. No ZarJiynchus in the tree." This is my last record of 

 Cassidix for the season, though observations were continued until 

 April 1. 



In these ob;r;ervations the long flights, the visits of inspection and 

 the forced entrance into nests are of interest. If Cassidix is para- 

 sitic only on species of the oropendola-cacique group it must cover 

 comparatively great distances in its search for a host. In my ex- 

 perience the nesting places of colonial birds of the same species 

 are not close together. On Barro Colorado, for example, as we have 

 seen, only three colonies of Zarhynchus are known. Cassidix, there- 

 fore, must not only cover much territory but presumably she must 

 be aware of the stage of the nesting season wdiich has beeJi reached 

 by her prospective hosts. It would be useless to deposit eggs in 

 the nests of birds not prepared to incubate them. Unless, therefore, 

 Cassidix can control the development of her ovaries she must either 

 waste eggs or know where to place them to advantage. 



Leyatus albicoUis. — An unexpected result of my studies of ZarAj/n- 

 chus is the discovery that it is parasitized by Leyatus alhicollis. In 

 each of the three nesting seasons devoted to the oropendolas a pair of 

 these flycatchers made their home in the nest tree and constantly 

 harried the oropendolas for the purpose of gaining possession of one 

 or more of their nests. Leyatus was also found in the two other 

 known nesting colonies of Zarhynchus on Barro Colorado, and its 

 association with Zarhynchus^ at least on this island, appears therefore 

 to be habitual. It will be interesting to learn whether it parasitizes 

 other oropendolas. It arrives at about the time or even before the 

 oropendola nests are completed and remains throughout their nesting 

 season. In the morning it appears in the nest tree within a minute 

 or two after the first Zarhynchus call is heard and it remains there 

 until evening. It was never seen to feed from or near the nest tree 

 but at intervals of an hour or more it darted to the adjoining forest 

 evidently for food, but was rarely absent more than three minutes. 



