168 Crossing the North and South African Ostrich 



Bald Head Patch. 



The crown of the head of the South African ostrich is covered with 

 short, hair-like feathers, which often form a tuft of longer hairs in the 

 middle. A bare pineal spot^ present in all ostriches at the back of the 

 head, is so small in the adult as to be only noticeable when the feathers 

 are turned aside. The North African ostrich on the other hand is 

 distinguished by having the top of the head for the most part naked, a 

 bald patch beginning at the back and extending forwards in a shield- 

 like fashion between the eyes (Text-fig. 1, p. 158). The area is roughly 

 pear-shaped, but may be partly divided down the middle. In diagnostic 

 descriptions the baldness is considered to be a character of some 

 importance in separating the northern species from the southern and 

 is even mentioned in the writings of Pliny 2. 



The extent and shape of the naked space vary a little in different 

 ostriches, but all the North African birds at Grootfontein display it to 

 a greater or less degree. It is quite independent of the pineal spot, and 

 its posterior border may either include this (Text-fig. 1) or pass in front 

 of it. In some birds, instead of forming a continuous patch, it is divided 

 more or less down the middle, having then a decided bilaterality. Often 

 a tuft of long, hair-like feathers remains towards the middle of the 

 hinder border, corresponding with the tuft in the southern bird, and 

 gradually disappears forwards. The area is covered with a horny, scurfy 

 layer, which peels off at times, exposing a fresh, clean surface of the 

 skin with the hard bony skull immediately below. 



The baldness is not apparent in the North African ostrich chick 

 when first hatched. At that time the head is covered with short bristly 

 down as in the South African, and the character becomes established in 

 the course of the first six months or so of growth. It is gradually 

 formed by the dropping out of the hairy feathers from about two months 

 onwards, and in a batch of chicks of the same age practically all stages 

 in the loss can be observed, the feathers to remain longest being those 

 of the middle tuft. No sharp line of separation occurs between the 

 naked and the covered part of the head ; a few stunted feathers represent 



1 An extra-cranial pineal body has lately been discovered in the ostrich. At a certain 

 stage of development it shows as a black pigmented area or vesicle which later disappears, 

 and only a dark, oval area, devoid of feathers remains in the newly hatched chick and per- 

 sists throughout life. Apparently the ostrich is the only bird with such a well-defined 

 pineal body, recalling that of the reptilia and persisting as a pineal spot. 



'^ Hist. Mund. lib. xi. cap. xxxvii. 



