404 



Human Influences — Our Living Re\<ii<rces 



Table 3. Geographn. distiibulion (if niunir (>5(J0 birds) die-offs of wild hirds by cause, 1983-93. 



Disease 



Cause 



States (number of events) 



5-9 



>9 



C0(1), VT(1) 



AR(1), C0(2), KS{2), U\(2), MD(2) ID(7) CA(80), MT(14) 



Ml(1), MN(1), NM(1), NY(1), 0H(2) NB(5) ND(25), SD(14) 



0K(1), OR(4),WI(3) NV(5) UT(11) 



C0(3), IA(4), ID(1),ME(1), MN(3) M0(5) CA(21), NB(13) 



0R(1), NM(4|,NV(1). SD(1) TX(18) 



ND(1) 



MD(1) 



TX(3) 



CA(1) 



ND(3), SD(1) 



MN(1), ND(2), SD(1) 



CA(2),VT(1).WA(1) 



Environmental conlaminanis AZ(1), CA(2), IL(1), NV(1), VA(1) 

 CA(1), NM(1) 



Fig. 5. Number of wild bird die- 

 off events listed in the National 

 Wildlife Health Center data base, 

 1981-93. 



Wetland losses, for example, are well docu- 

 mented and clearly a contiibuting factor in the 

 spread of avian cholera. California, a focal point 

 for the occunence and spread of avian cholera 

 in waterfowl, lost 91% of its historical wetland 

 acreage by 1980 (Dahl 1990). A similar situa- 

 tion exists in the Rainwater Basin of Nebraska 

 where avian cholera first appeared in waterfowl 

 in 1975; this area has subsequently become a 

 focal point for spread to other areas. About 90% 

 of historical wetland acreage within the 

 Rainwater Basin has been lost (Farrar 1980). 

 The association between wetland losses and 

 spread of infectious disease is due to the inter- 

 active factors that aid disease transmission. 



Habitat (environment) loss often results in 

 crowding birds on the remaining habitat, there- 

 by enhancing the potential for transmission of 

 infectious agents. Movement patterns of infect- 

 ed birds can spread the disease to other loca- 

 tions and populations and help establish the dis- 

 ease as a recurring problem. 



High concentrations of birds for prolonged 

 periods of time on limited habitat often degrade 

 the quality of habitat through fecal contamina- 

 tion and damage to vegetation. Deposition and 



220. 



200 . 



I" h-n 



o 140 BM ■ M M 



irih 



120 . 



100. 



80. 



II I 



81 82 83 84 85 86 87 88 89 90 91 

 Year 



survival of pathogenic parasites and microbes 

 are aided by such environtnental conditions and 

 can result in enhanced disease maintenance and 

 spread. 



Habitat degradation due to human-caused 

 factors is also important. For example, although 

 the bacterium responsible for avian botulism is 

 a common inhabitant of wetland substrates, the 

 production of the botulinum toxin that causes 

 botulism is dependent on specific environmen- 

 tal factors such as ambient temperature, pH, 

 oxygen depletion, and other factors (Locke and 

 Friend 1987). Discharges into wetlands of 

 sewage, agricultural chemicals, and poultry 

 wastes from factories have frequently been 

 associated with eruptions of avian botulism, 

 although cause and effect relationships have not 

 been clearly established. 



Prevention of Avian Diseases 



Diseases affecUng wild birds can be prevent- 

 ed and controlled despite the challenges of deal- 

 ing with species and populations that are often 

 highly mobile and spend much or all of their 

 lives in remote areas. 



Methodical monitoring and surveillance pro- 

 grams are needed to provide early detection of 

 emerging problems so that intervention can 

 begin when problems are most manageable. 

 Accurate diagnostic assessments of the causes 

 of morbidity and mortality are essential for 

 focusing control efforts. Also, greater emphasis 

 is needed on studies of disease ecology to pro- 

 vide enhanced understanding of host-agent- 

 environment relationships for specific diseases. 

 This information serves to identify weak links 

 where disease-control and prevention efforts 

 will be most effective. Molecular biology and 

 the associated field of genetic engineering will 

 greatly assist these efforts. 



References 



Dahl, T.E. 1990. Wetland losses in the United States 1780"s 

 to 1980's. U.S. Fish and Wildlife Service. Washington. 

 DC. 13 pp. 



Farrar. J. 1980, The Rainwater Basin . . . Nebraska's van- 

 ishing wetlands. Nebraska Game and Parks Commission. 

 Lincoln. 15 pp. 



Friend, M. 1987. Avian cholera. Pages 69-82 in M. Fnend 

 and C.J. Laitman. eds. Field guide to wildlife diseases. 

 Vol. 1. General field procedures and diseases of migrato- 

 ry birds. U.S. Fish and Wildlife Service Resour. Publ. 

 167. 



Friend. M. 1992. Environmental influences on major dis- 

 eases. Transactions of the North American Wildlife and 

 Natural Resour. Conference .57:517-525. 



Friend. M.. and G.L. Pearson. 1973. Duck plague; the pre- 

 sent situation. Proceedings of the Western Association of 

 State Game and Fish Commissioners 53:315-325. 



Kalmbach. E.R., and M.F. Gunderson. 1934. Western duck 

 sickness: a form of botulism. U.S. Department of 

 Agnculture Tech. Bull. 411. 81 pp. 



