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Agriculti 

 Survey 



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ficem'ber 



1937 

 ^^ 



mSHAZS AS . A F ACTOR IN G-AMD ?LUC? aATIO!T 



By J, 3, Shillin.^er, Sonior Vetorinaxiai:, Section of Diser.so Control 



Division of Wildlife Research. 



I'or raroiy yeai's trappers, huntors, and garns protectors liave noted 

 great fluctuations in tho a'D-imdajico of certain game aiid fur ppecie.'s* 

 These are often so pronounced that in times of greatest scarcity preda- 

 tors that feed upon the depleted species likewise "bccoma seriously reduo- 

 ed in nunbors. These periods of abundance and. scarcity were noted oj 

 trappers in the early history of the cou:atr;y, as their catch of foxes, 

 coyotesj ^7olves, aid other carnivorous fur animals was largely depend- 

 ent upon the ahundance of g;3mc, especially grouse and h-ai'es» upon which 

 the Carnivores fod» 



With the grouse and mre, tho cycle from peak of a"bu_".dance to 

 greatest r.carcity and hack to maximum ahimdance avcrad;3s aoout 10 years, 

 hut among some animal-.-, as chj.pnunks and field mice, the cycle may be 

 completed in 3 to 3 years. Tho shortage in tho numbers of the game spe- 

 cies discourager. hunting, and the fail^jre of sportsmen to p^jxcha.se hunt- 

 ing licenses causes loss of revenue to State conservation departments. 



Cooperative Study of Causes 



Tncse f lac t^jat ions in animal populations are more evident in the 

 Northeni States than in the Soathern. 7ot the past 10 years, therefore, 

 the Section of Disease Control of the B'Oi'eau of Biological Survey, in 

 cooperation with the Department of Bacteriolog;/ of the Jniversity of 

 Minnesota and the Ifinnesota State Conservation Commission, h^s made a 

 special study of the cycles of ab^undance rjnd sc;;.rcity. Opinions have 

 been advanced th^o.t tho decrease in game poprdations is due to a shortage 

 of food, to unfavorable weather in tho breeding season, or to an ovei'- 

 abimdaticc of predators. More recent studies hiave revealed, however, tliat 

 great reduction in numbers of game ranmmals and birds has occuird long 

 after tho end of the breeding period, during favorable seasons, or in the 

 absence of an excessive number of prodacloas a-i:aals. This would indicate 

 that these reductions are diie to some iinseen doRtructivo agency that t-alces 

 a large toll without exciting notice, 



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