KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 47. NIO 5. 9S 



Two days before an adult female of the same kind had been shot at the same place. At 

 the Homestead, Nairobi, a young bird in which the breast still was streaked with black 

 but the head already quite black had been shot he 29 th of Dec. 1910 in comparativcl v 

 open country with scattered trees. I thus got the impression that the Oriole of the country 

 round Nairobi belonged to the race O. 1. rolleti. 



The 31th of Jan. I shot a beautiful male Oriole in a forest near Meru borna. When 

 I had returned to the camp I showed this bird to Mr. Bl. Percival, who then happened 

 to be there, and he pointed out to me that this specimen, as its black median tail feathers 

 proved, belonged to the race which he had discovered, and which had been named after 

 him. Two days låter I succeeded in shooting a similar bird in a forest two hours march 

 north of Meru borna, and I saw several more there. 



In the beginning of April when I had returned to Nairobi I shot a typical O. 1. per- 

 civali in the forest reserve at the Limuru road in the same place where I had shot O. 1. 

 rolleti before. But in addition to this I shot the same day, and at the same place a speci- 

 men which was intermediate between the two, rolleti and percivali, viz. in which the me- 

 dian rectrices were olive green on the greater part of the web, but with black centre and 

 black tip (conf. theplate). A female from the same place was similar. Then some doubts 

 arose about the constancy of both forms. With regard to their dimensions both forms 

 appear to very much alike as far as my material is concerned as the f ollowing measurements 

 pro ve: 



Length of wing 



A. J 1 of »0. 1. percivali-» from Meru boma 31 /i 133 mm. 



B. » » » » » » » s /s 133 » 



C. » » » » Nairobi °U 130 » 



I). » » » (intermediate) from Nairobi 9 /* 129 » 



E. » » »0. /. rolleti» » » 2 /i 130 » 



F. $ » » » » » 30 /i2 130 » 



G. » » » » (intermediate) 9 /* 132 » 



H. juv. » » » 29 /i2 124 » 



The size of the bill is somewhat variable. The length of the culmen is in A — 24,5 

 mm; in B — 23 mm; in C — 25 mm; in D -- 22 mm; in E — 22,5 mm; in F — 23 mm; 

 in G — 23,5 mm. The specimens with the largest bilis are undoubtedly the oldest birds, 

 but it must be remembered that all these A to G are adult and breeding brids. B for 

 instance had the testidés strongly swelled, although its bill was among the shorter. 



The question is then in which relation do these differently coloured birds stånd to 

 each other? The easiest is to assume that the birds with pure black tail feathers are fully 

 adult, or the most highly developed birds, and that younger stages have the median rec- 

 trices more or less green. It is very possible that so is the case, and, if this is correct, all 

 my specimens should be different stages of percivali, although it must be admitted that 

 there is some irregularity in the assuming of the perfect plumage. This is, however, not 

 an uncommon thing among some species of birds. 



But all difficulties are not put to the side by such a theory. 0. percivali has been 

 recorded from many places now. It was discovered in the Kikuyu forest, and has then 

 been obtained from Elgon, Nandi and finally as far east as in the Mpanga forest. The 

 fact that I found it common as well at Nairobi as near Meru boma makes it probable that 



