ON THE PAIRING AND INCUBATION OF BIRDS. 59 



gamous, and of course pair, others are ^polygamous, and 

 never, unless compelled, confine themselves to individual 

 association. 



All the rapacious tribes belong \o the monogamous class ; 

 the same may be said of the Perchers ; the Pigeon tribe 

 are also generally monogamous ; so also appear to be all 

 llie strutkious class; but the aquatic birds and leaders vary 

 in this respect ; some are monogamous; others polygamous. 

 The gallinaceous tribe are generally polygamous. Although 

 the puerile notion that birds pair on Valentine's day in this 

 country is not, of course, entitled to the slightest credit, yet 

 there is no question, however, that about that period, or 

 sooner or later in the spring, many birds cease their grega- 

 rious association, and meet only in pairs for the performance 

 of the important office of incubation and rearing their 

 young. Whether this association in pjiirs continue for 

 more than one season by the same birds does not appear to 

 be yet accurately ascertained. The Cuckoo is also said to 

 be a pol}gamist; but we do not jct know sufficient of the 

 habits of this bird. 



There is one other fact relative to the change in the plu- 

 mage of birds which may be mentioned here, namely, that 

 sometimes the female assumes the feathers and appearance 

 of the male bird ; this has been noticed in the Common 

 Hen, the Pea-hen, and a lew others ; and as this change 

 has been most commonly observed in old birds, it has been 

 attributed to age alone ; but some late observations tend 

 to prove that the change arises from some disease of the 

 genital organs in female birds : for some young female 

 birds have also been observed with male feathers ; and 

 dissections in ail prove the diseased state of those organs. ' 



Although the Periods of the Incubation of Birds are 

 generally pretty regular, they are by no means exactly so, 



