28o BIRD BEHAVIOUR 



even birds which are social in winter nest in separate 

 pairs, though associations of two males and one 

 female, or vice versa, have been recorded ; and 

 polygamy is well known in many game-birds and 

 in Whydah-birds {Viduince), while polyandry appears 

 to be normal in Hemipodes and Tinamous, and 

 the parasitic nesters like Cuckoos and Cow-birds 

 are credited with promiscuity. 



Generally, however, the pair are faithful, not 

 only for the season, but, so far as evidence goes, 

 for several years, probably until a stronger rival 

 ousts the older and weaker partner, for strength 

 appears to be the chief determining factor in bird 

 marriage. At the same time, sentiment presum- 

 ably has something to do with it, because one so 

 often sees cross-matings among the various species 

 of Geese kept in our parks ; Geese are very intelli- 

 gent, and not very amorous, and wild hybrids 

 among them are practically unknown, so that it 

 would seem that these irregular alHances are dic- 

 tated by congeniality of disposition where there 

 are but few of each species to choose from. 



