with Uncle Sam's Naturalists 



- 2 ~ 



4-7-33 



United States Biolo^cal Survey, thinks we may have under- rated one important 

 cause of wild-life cycles; namely, disease. 



Vetei^r, - woodsmen may tell yoxi that wild animals and "birds never die of 

 disease in their natural environment. They may say oirds and animals catch dis- 

 ease only when kept in confinement. Wild birds and animals are more, likely to 

 suffer from disease when you keep then penned up than when they run loose in 

 nature. But, the naturalists do find disease among wild ducks, and quail, and 

 pheascnts, and foxes, and ouskrats, rnd deer just as you do among domestic poul- 

 try and livestock. What's more, they are beginning to see how disea,se may be 

 an importrnt factor in the wild-life cycles we have been talking about. 



In fcict, Doctor Shillinger and others suspect that disease has a g:reat 

 deal to do with the ebb and flow of the rabbit and grouse population in Minneso- 

 ta, and Wisconsin, and other northern states. In this region the ra.bbit and 

 grouse population took a tail-spin during the years of 1924, '25, and '26, but 

 since '26, the number of rabbits and grouse has been climbing and climbing, Kight 

 now, the naturalists figure rabbits are scampering around over parts of Minneso- 

 ta, and Wisconsin, and Michigan at the rate of about 300 to the square mle. 

 That's certainly a mess of rabbits. But in a year or two the rabbit and grouse 

 population is likely to hit another low point. The naturalists say this because 

 during the time conditions have been studied in this country the cycle of rabbit 

 and grouse population seems to jibe pretty well with the Hudson's Bay Company's 

 records of 10-year wild- life cycles in Canada, 



Dr. Shillinger, Dr. R. G. Green at the University of Minnesota, and offi- 

 cials of the Minnesota State Department of Conservation, have been conducting a 

 study of disease- not only diseases of rabbits and grouse, but also of other wild 

 life of the northern forests. 



So far, Shillinger and the Minnesota men have singled out three infec- 

 tious diseases that might sweep through the forests and kill off game in big 

 numbers. 



The most common of those diseases seems to be tularemia. Tularemia is the 

 same thing as the rabbit fever you've heard so much about in the last few years. 

 But tularemia isn't a disease of rabbits alone. During the past year, the wild- 

 life men discovered tularemia among ruffed and sharp- tailed grouse, Thoy aren't 

 ready to say tularemia occurs among birds in epizootic form — or that it is the 

 cause of the cycles we find in bird life. But they do know that tularemia is a 

 common infectious disease among rabbits. 



Other newly discovered diseases are a filterable virus disease found in 

 owls and a pseudo- tuberculosi s found in beavers and nuskrats and possibly affect- 

 ing a wide variety of other wild animals. 



How, if those three diseases are in any way responsible for those cycles, 

 why does the wild-life come and go in 10-year periods? After tularemia, or some 

 other disea.ses, breaks lorse in the greaifc northern woods, why doesn't it run on 

 and on until it Idlls off all wild life? What stops the disease after it once 

 gets a start? 



