FUR ANIMALS 



1381 



a proper balance. We do not know, for example, whether we are 

 producing 10,000,000 muskrats a year and trapping 13,000,000 or 

 producing 5,000,000 and trapping 25,000,000. We can be pretty sure 

 that we are trapping more than we are producing; but it is important 

 to find out how many more. Almost every State has some fur 

 resources that are a source of income for some of its citizens. The 

 methods of handling these resources are almost entirely haphazard, 

 and in fact few State game and conservation commissions have given 

 sufficient serious thought to the matter. In most States there is no 

 provision for keeping a record of the furs taken each year. In the 

 case of some of the most valuable fur bearers — martens, fishers, 

 wolverines, and otters — the situation has become so serious that the 

 Bureau of Biological Survey has appealed to all State game and 

 conservation commissions to protect them with a 5-year closed period, 

 as the only way to forestall their extermination. 



REPRODUCTIVE CYCLES 



The usefulness of breeding data in this situation may be illustrated 

 by the case of the marten (fig. 1). At its experiment station near 

 Saratoga Springs, N. Y., established in 1923, the Bureau has been 

 studying the breeding and the gestation period of the marten. As a 

 result it has found that a period of 9% months elapses between the 

 time of copulation and birth. With so long a period of gestation, 

 many pregnant females are bound to be destroyed under the prevailing 

 system of open and close seasons. It is obvious that unless the 

 trapping season for a fur animal corresponds accurately with its 

 gestation-free period, the close season will not accomplish what it is 

 intended to: the prospective generation will be destroyed along with 

 the one trapped. Even this precaution, however, would be ineffective 

 in the case of the marten or the fisher, for their gestation periods are 

 too long. A 5- or 10-year closed period is necessary to prevent 

 local or even general extermination of these two fur animals. 



The available information on the reproductive cycles of the wild 

 fur-bearing animals is very meager. A review of the literature shows 

 that very little research has been conducted to determine their actual 

 breeding seasons, postnatal development, and gestation periods. 

 Practically all that is now known has been learned by observing the 

 living animals. Few investigators have studied actual embryological 

 material. The one outstanding contribution to the embryological 

 science of fur animals is that of Hartman, 1 of the Department of 

 Embryology, Carnegie Institution of Washington, at Baltimore, Md. 

 This paper presents a study of the physiology of growth and repro- 

 duction, the embryology, the rate of intra-uterine and postnatal 

 growth, and the breeding season. More information of this kind is 

 vitally important to any programs of conservation, restoration, 

 restocking, or transplanting, as well as to the success of any effort to 

 produce fur species in captivity. Conversely, it is also important 

 in successful control of noxious animals, which should be most inten- 

 sively hunted throughout the period preceding the arrival of the 

 young. Similarly important is definite knowledge of the molting and 



3 Hartman, C. G. the breeding season of the opossum (didelphis yirginiana) and the r ate of 



INTRA-UTERINE AND POSTNATAL DEVELOPMENT. JOUT. Morph. and Physiol. 46: 143-215. 1928. 



