130 SKXUAL DIMOKPHISM 



the blow was delivered not outwards but forwards and some- 

 what downwards. 



Our knowledge of the birds' habits is almost entirely 

 derived from Leguat's description. He says that they were 

 monogamous, and moreover paired for life, like modern 

 pigeons. The male and female incubated alternately, and 

 incubation lasted seven weeks. If a female came near the 

 nest, the female possessor drove it away, while if the intruder 

 were a male, he was attacked by the male. This is all far 

 from being in harmony with pronounced sexual dimorphism, 

 but other actions are mentioned which are probably more 

 relevant to the question in hand. To quote the original 

 words : " lis ne volent pas, leur ailes sont trop petits pour 

 soutenir le poids de leurs corps. lis ne s'en servent que pour 

 se battre, et pour faire le moulinet quand ils veulent s'appeler 

 Tun l'autre. Ils font avec vitesse vingt ou trente pirouettes 

 tout de suite du meme cote pendant l'espace de quatre ou 

 cinq minutes : le mouvement de leurs ailes fait alors un bruit 

 qui approche fort de celui d'un crecerelle,et on l'entend de plus 

 de deux cents pas." Thus, besides fighting with their wings,. 

 the birds, probably the males only, had a habit of twirling 

 round in one direction four or five minutes at a time, during 

 which process the wings made a noise like a rattle. The 

 anonymous manuscript, Relation de Vile Rodrigue, says that 

 the noise is made with the wings when the birds are angry, 

 and that the noise is like rumbling thunder : " le bruit 

 approche fort de celui du tonnerre qu'on a un peu de peine a 

 entendre." Neither of these descriptions attempts to explain 

 exactly how the noise, which evidently impressed the writers 

 as very remarkable, was produced. Judging from the shape 

 of the skeleton, I have come to the conclusion that the noise 

 was produced by the striking of the wings together in front 

 of the breast. In this case the wings would strike one 

 another exactly where the exostoses are situated, and thus 



