The breeding seasons of mammals in captivity



  • 1Representatives of 1049 different mammalian species have lived in the Gardens of the Zoological Society of London during the 110 years intervening between their foundation in 1828 and the end of 1937. 171 belonged to the Order Primates. 316 species, including 28 Primates, have bred.
  • 2The records of births have been analysed to show the season of the year which different species breed. A summary of the main results is given in section 5, p. 914 of the main body of the paper.
  • 3There is a major physiological difference between a species that never breeds except in a restricted season, and one that breeds evenly throughout the year. The gap between the two is bridged by those animals which, while they breed +nore or less continuously, show a marked seasonal variation in the incidence of births. Theoretically the distinction between the two types of breeding habit can be evaluated statistically, but a more direct way of approaching the problem is the comparison of birth records for successive ten-year periods. It has been found that the difference between a continuous and a seasonal breeder is often apparent in the records of the first ten years. Even a few birth records may sometimes indicate the breeding habit of a species, and occasionally of the entire genus of which it is a member.
  • 4The analysis of the breeding records of a species in successive periods has also occasionally revealed a change in the seasonal incidence of births. It is impossible to determine whether such changes reflect changed climat, ic, conditions or the different habits of different breeding stocks within a species.
  • 5An attempt has been made to compare the times when mammals from the southern hemisphere bear their young in London, with the times they breed in their natural habitat (and also to compare the times when mammals from the northern hemisphere breed in zoological collections in the southern hemisphere). There are some thirty-eight species about which the records are sufficient to indicate breeding habits on the two sides of the equator. Eleven breed continuously in captivity but do not appear to exhibit any marked monthly variation in birth rate on either side of the equator. Two species breed continuously in both the northern and southern hemispheres, with a seasonal peak of births which also appears to be the same on both sides of the equator. In the remaining twenty-five species most births appear to occur in different months on the two sides of the equator.
  • 6During the 1'10 years to which the present records relate, intergeneric crosses have occurred in the family Cercopit'hecidae ofthe order Primates, and in the family B0vida.e of the order Artiodactyh. A large number of interspecific hybrids have occurred in many orders and families.