FOREWORD 11 
We cannot mate mid animals and birds simply by 
putting males and females together in the same cage. 
Domestic mammals and birds usually mate under such 
conditions, but mid ones often refuse. Many mammals 
and probably all birds that are not polyandrous or 
polygamous reserve the right to select their mates, and if 
the sexes are put together by man they may view each 
other with indifference or with animosity. There are 
many males and females of the same species of mammals 
at the Zoological Garden that will not consent to live 
together. A male monkey in a cage with several females 
will very often select one female for his mate and will 
have nothing to do with the others. 
Among monkeys fertility varies greatly. It is not 
practical to determine the ratio among the various kinds, 
as some kinds are much commoner in zoological collec- 
tions than others. I think that in general the Old World 
monkeys (Cercopithecidce) are better breeders in cap- 
tivity than those of the New World (Cehidce). The 
anthropoid apes are very poor breeders indeed; of the 
many gibbons, orangs, and chimpanzees, that for years 
have been captive in Europe and America, it is probable 
that only the chimpanzee has bred, and that very rarely. 
Refusal to mate, sterility, infanticide by father and 
mother, and sexual killing keep down reproduction in 
zoological gardens; and the number of young ones is a 
good indication of the character of a garden and of the 
provisions made for the happiness, comfort and health of 
the animals. 
With the birds in a zoological garden the conditions 
for nesting and laying are not good. Caged birds have no 
material for a nest, no privacy and rarely lay an egg. 
The outdoor water birds and the outdoor upland birds 
with natural surroundings, with secluded retreats, lay 
and hatch very well. Birds like mammals apparently 
are indifferent to publicity when copulating, but seek 
